introduce memory hinting API for external process

PATCH Superseded Minchan Kim 4 participants 15 messages Feb 14, 2020 – Feb 19, 2020

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Minchan Kim

author

2020-02-14 17:05 UTC #0 lore raw

v5 cover introduce memory hinting API for external process

Now, we have MADV_PAGEOUT and MADV_COLD as madvise hinting API. With that, application could give hints to kernel what memory range are preferred to be reclaimed. However, in some platform(e.g., Android), the information required to make the hinting decision is not known to the app.
Instead, it is known to a centralized userspace daemon(e.g., ActivityManagerService), and that daemon must be able to initiate reclaim on its own without any app involvement.

To solve the concern, this patch introduces new syscall - process_madvise(2). Bascially, it's same with madvise(2) syscall but it has some differences.

1. It needs pidfd of target process to provide the hint
2. It supports only MADV_{COLD|PAGEOUT|MERGEABLE|UNMEREABLE} at this moment. Other hints in madvise will be opened when there are explicit requests from community to prevent unexpected bugs we couldn't support.
3. Only privileged processes can do something for other process's address space.

For more detail of the new API, please see "mm: introduce external memory hinting API" description in this patchset.

Minchan Kim (6):
mm: pass task to do_madvise
mm: introduce external memory hinting API
mm: validate mm in do_madvise
mm: check fatal signal pending of target process
pid: export pidfd_get_pid
mm: support both pid and pidfd for process_madvise

Oleksandr Natalenko (2):
mm/madvise: employ mmget_still_valid for write lock mm/madvise: allow KSM hints for remote API

* from v4 - https://lore.kernel.org/linux-mm/[email protected]/
* pass mm down to functions, not accessing task->mm - Jann
* clean up - Alexander
* add Reviewed-by - Alexander, SeongJae
* patch reordering

* from v3 - https://lore.kernel.org/linux-mm/[email protected]/
* verify task->mm aftere access_mm - Oleg
* split some patches for easy review - Alexander
* clean up fatal signal checking - Suren

* from v2 - https://lore.kernel.org/linux-mm/[email protected]/
* check signal callee and caller to bail out - Kirill Tkhai
* put more clarification for justification of new API

* from v1 - https://lore.kernel.org/linux-mm/[email protected]/
* fix syscall number - SeongJae
* use get_pid_task - Kirill Tkhai
* extend API to support pid as well as pidfd - Kirill Tkhai

Minchan Kim (5):
mm: pass task and mm to do_madvise
mm: introduce external memory hinting API
mm: check fatal signal pending of target process
pid: export pidfd_get_pid
mm: support both pid and pidfd for process_madvise

Oleksandr Natalenko (2):
mm/madvise: employ mmget_still_valid for write lock mm/madvise: allow KSM hints for remote API

 arch/alpha/kernel/syscalls/syscall.tbl      |   1 +
 arch/arm/tools/syscall.tbl                  |   1 +
 arch/arm64/include/asm/unistd.h             |   2 +-
 arch/arm64/include/asm/unistd32.h           |   2 +
 arch/ia64/kernel/syscalls/syscall.tbl       |   1 +
 arch/m68k/kernel/syscalls/syscall.tbl       |   1 +
 arch/microblaze/kernel/syscalls/syscall.tbl |   1 +
 arch/mips/kernel/syscalls/syscall_n32.tbl   |   1 +
 arch/mips/kernel/syscalls/syscall_n64.tbl   |   1 +
 arch/parisc/kernel/syscalls/syscall.tbl     |   1 +
 arch/powerpc/kernel/syscalls/syscall.tbl    |   1 +
 arch/s390/kernel/syscalls/syscall.tbl       |   1 +
 arch/sh/kernel/syscalls/syscall.tbl         |   1 +
 arch/sparc/kernel/syscalls/syscall.tbl      |   1 +
 arch/x86/entry/syscalls/syscall_32.tbl      |   1 +
 arch/x86/entry/syscalls/syscall_64.tbl      |   1 +
 arch/xtensa/kernel/syscalls/syscall.tbl     |   1 +
 fs/io_uring.c                               |   2 +-
 include/linux/mm.h                          |   3 +-
 include/linux/pid.h                         |   1 +
 include/linux/syscalls.h                    |   3 +
 include/uapi/asm-generic/unistd.h           |   4 +-
 kernel/exit.c                               |  17 ---
 kernel/pid.c                                |  17 +++
 kernel/sys_ni.c                             |   1 +
 mm/madvise.c                                | 142 ++++++++++++++++----
 26 files changed, 165 insertions(+), 44 deletions(-)

Signature · 1 line

2.25.0.265.gbab2e86ba0-goog

Minchan Kim

author

2020-02-14 17:06 UTC #1 lore raw

PATCH v5 1/7 mm: pass task and mm to do_madvise

In upcoming patches, do_madvise will be called from external process context so we shouldn't asssume "current" is always hinted process's task_struct. Furthermore, we couldn't access mm_struct via task->mm once it's verified by access_mm which will be introduced in next patch[1]. And let's pass *current* and current->mm as arguments of do_madvise so it shouldn't change existing behavior but prepare next patch to make review easy.

[1] http://lore.kernel.org/r/CAG48ez27=pwm5m_N_988xT1huO7g7h6arTQL44zev6TD-h-7Tg@mail.gmail.com

Cc Jann Horn <[email protected]>

Signed-off-by Minchan Kim <[email protected]>

---
 fs/io_uring.c      |  2 +-
 include/linux/mm.h |  3 ++-
 mm/madvise.c       | 34 +++++++++++++++++++---------------
 3 files changed, 22 insertions(+), 17 deletions(-)

fs/io_uring.c +1 -1

index 63beda9bafc5..bf111675307c 100644
@@ -2736,7 +2736,7 @@ static int io_madvise(struct io_kiocb *req, struct io_kiocb **nxt,
 	if (force_nonblock)
 		return -EAGAIN;
 
-	ret = do_madvise(ma->addr, ma->len, ma->advice);
+	ret = do_madvise(current, current->mm, ma->addr, ma->len, ma->advice);
 	if (ret < 0)
 		req_set_fail_links(req);
 	io_cqring_add_event(req, ret);

include/linux/mm.h +2 -1

index 52269e56c514..beb9259f9ed1 100644
@@ -2323,7 +2323,8 @@ extern int __do_munmap(struct mm_struct *, unsigned long, size_t,
 		       struct list_head *uf, bool downgrade);
 extern int do_munmap(struct mm_struct *, unsigned long, size_t,
 		     struct list_head *uf);
-extern int do_madvise(unsigned long start, size_t len_in, int behavior);
+extern int do_madvise(struct task_struct *task, struct mm_struct *mm,
+		unsigned long start, size_t len_in, int behavior);
 
 static inline unsigned long
 do_mmap_pgoff(struct file *file, unsigned long addr,

mm/madvise.c +19 ~~-15~~

index 43b47d3fae02..24566f59b89b 100644
@@ -254,6 +254,7 @@ static long madvise_willneed(struct vm_area_struct *vma,
 			     struct vm_area_struct **prev,
 			     unsigned long start, unsigned long end)
 {
+	struct mm_struct *mm = vma->vm_mm;
 	struct file *file = vma->vm_file;
 	loff_t offset;

@@ -288,12 +289,12 @@ static long madvise_willneed(struct vm_area_struct *vma,
 	 */
 	*prev = NULL;	/* tell sys_madvise we drop mmap_sem */
 	get_file(file);
-	up_read(&current->mm->mmap_sem);
+	up_read(&mm->mmap_sem);
 	offset = (loff_t)(start - vma->vm_start)
 			+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
 	vfs_fadvise(file, offset, end - start, POSIX_FADV_WILLNEED);
 	fput(file);
-	down_read(&current->mm->mmap_sem);
+	down_read(&mm->mmap_sem);
 	return 0;
 }

@@ -676,7 +677,6 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 	if (nr_swap) {
 		if (current->mm == mm)
 			sync_mm_rss(mm);
-
 		add_mm_counter(mm, MM_SWAPENTS, nr_swap);
 	}
 	arch_leave_lazy_mmu_mode();

@@ -756,6 +756,8 @@ static long madvise_dontneed_free(struct vm_area_struct *vma,
 				  unsigned long start, unsigned long end,
 				  int behavior)
 {
+	struct mm_struct *mm = vma->vm_mm;
+
 	*prev = vma;
 	if (!can_madv_lru_vma(vma))
 		return -EINVAL;

@@ -763,8 +765,8 @@ static long madvise_dontneed_free(struct vm_area_struct *vma,
 	if (!userfaultfd_remove(vma, start, end)) {
 		*prev = NULL; /* mmap_sem has been dropped, prev is stale */
 
-		down_read(&current->mm->mmap_sem);
-		vma = find_vma(current->mm, start);
+		down_read(&mm->mmap_sem);
+		vma = find_vma(mm, start);
 		if (!vma)
 			return -ENOMEM;
 		if (start < vma->vm_start) {

@@ -818,6 +820,7 @@ static long madvise_remove(struct vm_area_struct *vma,
 	loff_t offset;
 	int error;
 	struct file *f;
+	struct mm_struct *mm = vma->vm_mm;
 
 	*prev = NULL;	/* tell sys_madvise we drop mmap_sem */

@@ -845,13 +848,13 @@ static long madvise_remove(struct vm_area_struct *vma,
 	get_file(f);
 	if (userfaultfd_remove(vma, start, end)) {
 		/* mmap_sem was not released by userfaultfd_remove() */
-		up_read(&current->mm->mmap_sem);
+		up_read(&mm->mmap_sem);
 	}
 	error = vfs_fallocate(f,
 				FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
 				offset, end - start);
 	fput(f);
-	down_read(&current->mm->mmap_sem);
+	down_read(&mm->mmap_sem);
 	return error;
 }

@@ -1044,7 +1047,8 @@ madvise_behavior_valid(int behavior)
  *  -EBADF  - map exists, but area maps something that isn't a file.
  *  -EAGAIN - a kernel resource was temporarily unavailable.
  */
-int do_madvise(unsigned long start, size_t len_in, int behavior)
+int do_madvise(struct task_struct *task, struct mm_struct *mm,
+		unsigned long start, size_t len_in, int behavior)
 {
 	unsigned long end, tmp;
 	struct vm_area_struct *vma, *prev;

@@ -1082,10 +1086,10 @@ int do_madvise(unsigned long start, size_t len_in, int behavior)
 
 	write = madvise_need_mmap_write(behavior);
 	if (write) {
-		if (down_write_killable(&current->mm->mmap_sem))
+		if (down_write_killable(&mm->mmap_sem))
 			return -EINTR;
 	} else {
-		down_read(&current->mm->mmap_sem);
+		down_read(&mm->mmap_sem);
 	}
 
 	/*

@@ -1093,7 +1097,7 @@ int do_madvise(unsigned long start, size_t len_in, int behavior)
 	 * ranges, just ignore them, but return -ENOMEM at the end.
 	 * - different from the way of handling in mlock etc.
 	 */
-	vma = find_vma_prev(current->mm, start, &prev);
+	vma = find_vma_prev(mm, start, &prev);
 	if (vma && start > vma->vm_start)
 		prev = vma;

@@ -1130,19 +1134,19 @@ int do_madvise(unsigned long start, size_t len_in, int behavior)
 		if (prev)
 			vma = prev->vm_next;
 		else	/* madvise_remove dropped mmap_sem */
-			vma = find_vma(current->mm, start);
+			vma = find_vma(mm, start);
 	}
 out:
 	blk_finish_plug(&plug);
 	if (write)
-		up_write(&current->mm->mmap_sem);
+		up_write(&mm->mmap_sem);
 	else
-		up_read(&current->mm->mmap_sem);
+		up_read(&mm->mmap_sem);
 
 	return error;
 }
 
 SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
 {
-	return do_madvise(start, len_in, behavior);
+	return do_madvise(current, current->mm, start, len_in, behavior);
 }

Signature · 1 line

2.25.0.265.gbab2e86ba0-goog

Jann Horn

reviewer

2020-02-14 17:25 UTC #2 lore raw

Re: [PATCH v5 1/7] mm: pass task and mm to do_madvise

+Jens and io-uring list

Quoted 3 lines · Minchan Kim

In upcoming patches, do_madvise will be called from external process context so we shouldn't asssume "current" is always hinted process's task_struct.

[...]

Quoted 1 line

[1] http://lore.kernel.org/r/CAG48ez27=pwm5m_N_988xT1huO7g7h6arTQL44zev6TD-h-7Tg@mail.gmail.com

[...]

Quoted 1 line

fs/io_uring.c +0 -0

[...]

fs/io_uring.c static int io_madvise(struct io_kiocb *req, struct io_kiocb **nxt, · line 2742

Quoted 9 lines

fs/io_uring.c +1 -1

@@ -2736,7 +2736,7 @@ static int io_madvise(struct io_kiocb *req, struct io_kiocb **nxt,
        if (force_nonblock)
                return -EAGAIN;
 
-       ret = do_madvise(ma->addr, ma->len, ma->advice);
+       ret = do_madvise(current, current->mm, ma->addr, ma->len, ma->advice);
        if (ret < 0)
                req_set_fail_links(req);
        io_cqring_add_event(req, ret);

Jens, can you have a look at this change and the following patch
<https://lore.kernel.org/linux-mm/[email protected]/>
("[PATCH v5 3/7] mm: check fatal signal pending of target process")? Basically Minchan's patch tries to plumb through the identity of the target task so that if that task gets killed in the middle of the operation, the (potentially long-running and costly) madvise operation can be cancelled. Just passing in "current" instead (which in this case is the uring worker thread AFAIK) doesn't really break anything, other than making the optimization not work, but I wonder whether this couldn't be done more cleanly - maybe by passing in NULL to mean "we don't know who the target task is", since I think we don't know that here?

Jens Axboe

maintainer

2020-02-14 18:22 UTC #3 lore raw

Re: [PATCH v5 1/7] mm: pass task and mm to do_madvise

Quoted 25 lines · Jann Horn

+Jens and io-uring list
Quoted 3 lines · Minchan Kim
In upcoming patches, do_madvise will be called from external process context so we shouldn't asssume "current" is always hinted process's task_struct.
[...]
Quoted 1 line
[1] http://lore.kernel.org/r/CAG48ez27=pwm5m_N_988xT1huO7g7h6arTQL44zev6TD-h-7Tg@mail.gmail.com
[...]
Quoted 1 line
fs/io_uring.c +0 -0
[...]
fs/io_uring.c static int io_madvise(struct io_kiocb *req, struct io_kiocb **nxt, · line 2742
Quoted 9 lines
fs/io_uring.c +1 -1
@@ -2736,7 +2736,7 @@ static int io_madvise(struct io_kiocb *req, struct io_kiocb **nxt,
        if (force_nonblock)
                return -EAGAIN;
 
-       ret = do_madvise(ma->addr, ma->len, ma->advice);
+       ret = do_madvise(current, current->mm, ma->addr, ma->len, ma->advice);
        if (ret < 0)
                req_set_fail_links(req);
        io_cqring_add_event(req, ret);
Jens, can you have a look at this change and the following patch
<https://lore.kernel.org/linux-mm/[email protected]/>
("[PATCH v5 3/7] mm: check fatal signal pending of target process")? Basically Minchan's patch tries to plumb through the identity of the

Quoted 8 lines

target task so that if that task gets killed in the middle of the operation, the (potentially long-running and costly) madvise operation can be cancelled. Just passing in "current" instead (which in this case is the uring worker thread AFAIK) doesn't really break anything, other than making the optimization not work, but I wonder whether this couldn't be done more cleanly - maybe by passing in NULL to mean "we don't know who the target task is", since I think we don't know that here?

Thanks for bringing this to my attention, patches that touch io_uring (or anything else) really should be CC'ed to the maintainer(s) of those areas...

Yeah, the change above won't do the right thing for io_uring, in fact it'll always be the wrong task. So I'd second Jann's question, and ask if we really need the actual task, or if NULL could be used? For cancelation purposes, I'm guessing you want the task that's actually doing the operation, even if it's on behalf of someone else. That makes the interface a bit weird, as you'd assume the task/mm passed in would be related to the madvise itself, not just for cancelation.

Would be nice with some clarification, so we can figure out an approach that would actually work.

Signature · 1 line

Jens Axboe

Minchan Kim

author

2020-02-14 18:45 UTC #4 lore raw

Re: [PATCH v5 1/7] mm: pass task and mm to do_madvise

Quoted 35 lines · Jens Axboe

Quoted 25 lines · Jann Horn
+Jens and io-uring list
Quoted 3 lines · Minchan Kim
In upcoming patches, do_madvise will be called from external process context so we shouldn't asssume "current" is always hinted process's task_struct.
[...]
Quoted 1 line
[1] http://lore.kernel.org/r/CAG48ez27=pwm5m_N_988xT1huO7g7h6arTQL44zev6TD-h-7Tg@mail.gmail.com
[...]
Quoted 1 line
fs/io_uring.c +0 -0
[...]
fs/io_uring.c static int io_madvise(struct io_kiocb *req, struct io_kiocb **nxt, · line 2742
Quoted 9 lines
fs/io_uring.c +1 -1
@@ -2736,7 +2736,7 @@ static int io_madvise(struct io_kiocb *req, struct io_kiocb **nxt,
        if (force_nonblock)
                return -EAGAIN;
 
-       ret = do_madvise(ma->addr, ma->len, ma->advice);
+       ret = do_madvise(current, current->mm, ma->addr, ma->len, ma->advice);
        if (ret < 0)
                req_set_fail_links(req);
        io_cqring_add_event(req, ret);
Jens, can you have a look at this change and the following patch
<https://lore.kernel.org/linux-mm/[email protected]/>
("[PATCH v5 3/7] mm: check fatal signal pending of target process")? Basically Minchan's patch tries to plumb through the identity of the
Quoted 8 lines
target task so that if that task gets killed in the middle of the operation, the (potentially long-running and costly) madvise operation can be cancelled. Just passing in "current" instead (which in this case is the uring worker thread AFAIK) doesn't really break anything, other than making the optimization not work, but I wonder whether this couldn't be done more cleanly - maybe by passing in NULL to mean "we don't know who the target task is", since I think we don't know that here?

Quoted 3 lines

Thanks for bringing this to my attention, patches that touch io_uring (or anything else) really should be CC'ed to the maintainer(s) of those areas...

Hi Jens, it was my mistake. Sorry for that.

Quoted 11 lines

Yeah, the change above won't do the right thing for io_uring, in fact it'll always be the wrong task. So I'd second Jann's question, and ask if we really need the actual task, or if NULL could be used? For cancelation purposes, I'm guessing you want the task that's actually doing the operation, even if it's on behalf of someone else. That makes the interface a bit weird, as you'd assume the task/mm passed in would be related to the madvise itself, not just for cancelation.
Would be nice with some clarification, so we can figure out an approach that would actually work.

MADV_(COLD|PAGEOUT) checks both caller and callee and the part aims for callee(ie, target task). Thus, we could pass NULL for io_madvise if it couldn't know who is target and let's have NULL check before the fatal_signal_pending. I will put following checks in [3/7].

	if (private->target_Task &&
			fatal_signal_pending(private->target_task))
		return -EINTR;

From d008a5a1049b03b3e0eeef7121faead2b6555f49 Mon Sep 17 00:00:00 2001
From: Minchan Kim <[email protected]>
Date: Fri, 14 Feb 2020 07:29:58 -0800
Subject: [PATCH] mm: pass task and mm to do_madvise

Note: io_madvise pass NULL as target_tas argument of do_madvise because it couldn't know who is target.

[1] http://lore.kernel.org/r/CAG48ez27=pwm5m_N_988xT1huO7g7h6arTQL44zev6TD-h-7Tg@mail.gmail.com

Cc Jens Axboe <[email protected]>

Cc Jann Horn <[email protected]>

Signed-off-by Minchan Kim <[email protected]>

---
 fs/io_uring.c      |  2 +-
 include/linux/mm.h |  3 ++-
 mm/madvise.c       | 34 +++++++++++++++++++---------------
 3 files changed, 22 insertions(+), 17 deletions(-)

fs/io_uring.c +1 -1

index 63beda9bafc5..1c7e9cd6c8ce 100644
@@ -2736,7 +2736,7 @@ static int io_madvise(struct io_kiocb *req, struct io_kiocb **nxt,
 	if (force_nonblock)
 		return -EAGAIN;
 
-	ret = do_madvise(ma->addr, ma->len, ma->advice);
+	ret = do_madvise(NULL, current->mm, ma->addr, ma->len, ma->advice);
 	if (ret < 0)
 		req_set_fail_links(req);
 	io_cqring_add_event(req, ret);

include/linux/mm.h +2 -1

index 52269e56c514..beb9259f9ed1 100644
@@ -2323,7 +2323,8 @@ extern int __do_munmap(struct mm_struct *, unsigned long, size_t,
 		       struct list_head *uf, bool downgrade);
 extern int do_munmap(struct mm_struct *, unsigned long, size_t,
 		     struct list_head *uf);
-extern int do_madvise(unsigned long start, size_t len_in, int behavior);
+extern int do_madvise(struct task_struct *task, struct mm_struct *mm,
+		unsigned long start, size_t len_in, int behavior);
 
 static inline unsigned long
 do_mmap_pgoff(struct file *file, unsigned long addr,

mm/madvise.c +19 ~~-15~~

index 43b47d3fae02..f75c86b6c463 100644
@@ -254,6 +254,7 @@ static long madvise_willneed(struct vm_area_struct *vma,
 			     struct vm_area_struct **prev,
 			     unsigned long start, unsigned long end)
 {
+	struct mm_struct *mm = vma->vm_mm;
 	struct file *file = vma->vm_file;
 	loff_t offset;

@@ -288,12 +289,12 @@ static long madvise_willneed(struct vm_area_struct *vma,
 	 */
 	*prev = NULL;	/* tell sys_madvise we drop mmap_sem */
 	get_file(file);
-	up_read(&current->mm->mmap_sem);
+	up_read(&mm->mmap_sem);
 	offset = (loff_t)(start - vma->vm_start)
 			+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
 	vfs_fadvise(file, offset, end - start, POSIX_FADV_WILLNEED);
 	fput(file);
-	down_read(&current->mm->mmap_sem);
+	down_read(&mm->mmap_sem);
 	return 0;
 }

@@ -676,7 +677,6 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 	if (nr_swap) {
 		if (current->mm == mm)
 			sync_mm_rss(mm);
-
 		add_mm_counter(mm, MM_SWAPENTS, nr_swap);
 	}
 	arch_leave_lazy_mmu_mode();

@@ -756,6 +756,8 @@ static long madvise_dontneed_free(struct vm_area_struct *vma,
 				  unsigned long start, unsigned long end,
 				  int behavior)
 {
+	struct mm_struct *mm = vma->vm_mm;
+
 	*prev = vma;
 	if (!can_madv_lru_vma(vma))
 		return -EINVAL;

@@ -763,8 +765,8 @@ static long madvise_dontneed_free(struct vm_area_struct *vma,
 	if (!userfaultfd_remove(vma, start, end)) {
 		*prev = NULL; /* mmap_sem has been dropped, prev is stale */
 
-		down_read(&current->mm->mmap_sem);
-		vma = find_vma(current->mm, start);
+		down_read(&mm->mmap_sem);
+		vma = find_vma(mm, start);
 		if (!vma)
 			return -ENOMEM;
 		if (start < vma->vm_start) {

@@ -818,6 +820,7 @@ static long madvise_remove(struct vm_area_struct *vma,
 	loff_t offset;
 	int error;
 	struct file *f;
+	struct mm_struct *mm = vma->vm_mm;
 
 	*prev = NULL;	/* tell sys_madvise we drop mmap_sem */

@@ -845,13 +848,13 @@ static long madvise_remove(struct vm_area_struct *vma,
 	get_file(f);
 	if (userfaultfd_remove(vma, start, end)) {
 		/* mmap_sem was not released by userfaultfd_remove() */
-		up_read(&current->mm->mmap_sem);
+		up_read(&mm->mmap_sem);
 	}
 	error = vfs_fallocate(f,
 				FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
 				offset, end - start);
 	fput(f);
-	down_read(&current->mm->mmap_sem);
+	down_read(&mm->mmap_sem);
 	return error;
 }

@@ -1044,7 +1047,8 @@ madvise_behavior_valid(int behavior)
  *  -EBADF  - map exists, but area maps something that isn't a file.
  *  -EAGAIN - a kernel resource was temporarily unavailable.
  */
-int do_madvise(unsigned long start, size_t len_in, int behavior)
+int do_madvise(struct task_struct *target_task, struct mm_struct *mm,
+		unsigned long start, size_t len_in, int behavior)
 {
 	unsigned long end, tmp;
 	struct vm_area_struct *vma, *prev;

@@ -1082,10 +1086,10 @@ int do_madvise(unsigned long start, size_t len_in, int behavior)
 
 	write = madvise_need_mmap_write(behavior);
 	if (write) {
-		if (down_write_killable(&current->mm->mmap_sem))
+		if (down_write_killable(&mm->mmap_sem))
 			return -EINTR;
 	} else {
-		down_read(&current->mm->mmap_sem);
+		down_read(&mm->mmap_sem);
 	}
 
 	/*

@@ -1093,7 +1097,7 @@ int do_madvise(unsigned long start, size_t len_in, int behavior)
 	 * ranges, just ignore them, but return -ENOMEM at the end.
 	 * - different from the way of handling in mlock etc.
 	 */
-	vma = find_vma_prev(current->mm, start, &prev);
+	vma = find_vma_prev(mm, start, &prev);
 	if (vma && start > vma->vm_start)
 		prev = vma;

@@ -1130,19 +1134,19 @@ int do_madvise(unsigned long start, size_t len_in, int behavior)
 		if (prev)
 			vma = prev->vm_next;
 		else	/* madvise_remove dropped mmap_sem */
-			vma = find_vma(current->mm, start);
+			vma = find_vma(mm, start);
 	}
 out:
 	blk_finish_plug(&plug);
 	if (write)
-		up_write(&current->mm->mmap_sem);
+		up_write(&mm->mmap_sem);
 	else
-		up_read(&current->mm->mmap_sem);
+		up_read(&mm->mmap_sem);
 
 	return error;
 }
 
 SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
 {
-	return do_madvise(start, len_in, behavior);
+	return do_madvise(current, current->mm, start, len_in, behavior);
 }

Signature · 1 line

2.25.0.265.gbab2e86ba0-goog

Jens Axboe

maintainer

2020-02-14 19:09 UTC #5 lore raw

Re: [PATCH v5 1/7] mm: pass task and mm to do_madvise

fs/io_uring.c static int io_madvise(struct io_kiocb *req, struct io_kiocb **nxt, · line 2742

Quoted 13 lines · Minchan Kim

fs/io_uring.c +1 -1

index 63beda9bafc5..1c7e9cd6c8ce 100644
@@ -2736,7 +2736,7 @@ static int io_madvise(struct io_kiocb *req, struct io_kiocb **nxt,
 	if (force_nonblock)
 		return -EAGAIN;
 
-	ret = do_madvise(ma->addr, ma->len, ma->advice);
+	ret = do_madvise(NULL, current->mm, ma->addr, ma->len, ma->advice);
 	if (ret < 0)
 		req_set_fail_links(req);
 	io_cqring_add_event(req, ret);

I think we want to use req->work.mm here - it'll be the same as current->mm at this point, but it makes it clear that we're using a grabbed mm.

Signature · 1 line

Jens Axboe

Minchan Kim

author

2020-02-14 19:31 UTC #6 lore raw

Re: [PATCH v5 1/7] mm: pass task and mm to do_madvise

Quoted 9 lines · Jens Axboe

Quoted 8 lines · Minchan Kim

fs/io_uring.c +0 -0

index 63beda9bafc5..1c7e9cd6c8ce 100644
@@ -2736,7 +2736,7 @@ static int io_madvise(struct io_kiocb *req, struct io_kiocb **nxt,
 	if (force_nonblock)
 		return -EAGAIN;

Quoted 9 lines

fs/io_uring.c static int io_madvise(struct io_kiocb *req, struct io_kiocb **nxt, · line 2742
Quoted 5 lines
fs/io_uring.c +1 -1
-	ret = do_madvise(ma->addr, ma->len, ma->advice);
+	ret = do_madvise(NULL, current->mm, ma->addr, ma->len, ma->advice);
 	if (ret < 0)
 		req_set_fail_links(req);
 	io_cqring_add_event(req, ret);
I think we want to use req->work.mm here - it'll be the same as current->mm at this point, but it makes it clear that we're using a grabbed mm.

Will fix at respin. Thanks for the review!

Minchan Kim

author

2020-02-14 17:06 UTC #7 lore raw

PATCH v5 2/7 mm: introduce external memory hinting API

In reply to Minchan Kim

There is usecase that System Management Software(SMS) want to give a memory hint like MADV_[COLD|PAGEEOUT] to other processes and in the case of Android, it is the ActivityManagerService.

It's similar in spirit to madvise(MADV_WONTNEED), but the information required to make the reclaim decision is not known to the app. Instead, it is known to the centralized userspace daemon(ActivityManagerService), and that daemon must be able to initiate reclaim on its own without any app involvement.

To solve the issue, this patch introduces a new syscall process_madvise(2). It uses pidfd of an external process to give the hint.

int process_madvise(int pidfd, void *addr, size_t length, int advise,

			unsigned long flag);

Since it could affect other process's address range, only privileged process(CAP_SYS_PTRACE) or something else(e.g., being the same UID) gives it the right to ptrace the process could use it successfully. The flag argument is reserved for future use if we need to extend the API.

I think supporting all hints madvise has/will supported/support to process_madvise is rather risky. Because we are not sure all hints make sense from external process and implementation for the hint may rely on the caller being in the current context so it could be error-prone. Thus, I just limited hints as MADV_[COLD|PAGEOUT] in this patch.

If someone want to add other hints, we could hear hear the usecase and review it for each hint. It's safer for maintenance rather than introducing a buggy syscall but hard to fix it later.

Q.1 - Why does any external entity have better knowledge?

Quote from Sandeep
"For Android, every application (including the special SystemServer) are forked from Zygote. The reason of course is to share as many libraries and classes between the two as possible to benefit from the preloading during boot.

After applications start, (almost) all of the APIs end up calling into this SystemServer process over IPC (binder) and back to the application.

In a fully running system, the SystemServer monitors every single process periodically to calculate their PSS / RSS and also decides which process is "important" to the user for interactivity.

So, because of how these processes start _and_ the fact that the SystemServer is looping to monitor each process, it does tend to *know* which address range of the application is not used / useful.

Besides, we can never rely on applications to clean things up themselves. We've had the "hey app1, the system is low on memory, please trim your memory usage down" notifications for a long time[1]. They rely on applications honoring the broadcasts and very few do.

So, if we want to avoid the inevitable killing of the application and restarting it, some way to be able to tell the OS about unimportant memory in these applications will be useful.

- ssp

Q.2 - How to guarantee the race(i.e., object validation) between when giving a hint from an external process and get the hint from the target process?

process_madvise operates on the target process's address space as it exists at the instant that process_madvise is called. If the space target process can run between the time the process_madvise process inspects the target process address space and the time that process_madvise is actually called, process_madvise may operate on memory regions that the calling process does not expect. It's the responsibility of the process calling process_madvise to close this race condition. For example, the calling process can suspend the target process with ptrace, SIGSTOP, or the freezer cgroup so that it doesn't have an opportunity to change its own address space before process_madvise is called. Another option is to operate on memory regions that the caller knows a priori will be unchanged in the target process. Yet another option is to accept the race for certain process_madvise calls after reasoning that mistargeting will do no harm. The suggested API itself does not provide synchronization. It also apply other APIs like move_pages, process_vm_write.

The race isn't really a problem though. Why is it so wrong to require that callers do their own synchronization in some manner? Nobody objects to write(2) merely because it's possible for two processes to open the same file and clobber each other's writes --- instead, we tell people to use flock or something. Think about mmap. It never guarantees newly allocated address space is still valid when the user tries to access it because other threads could unmap the memory right before. That's where we need synchronization by using other API or design from userside. It shouldn't be part of API itself. If someone needs more fine-grained synchronization rather than process level, there were two ideas suggested - cookie[2] and anon-fd[3]. Both are applicable via using last reserved argument of the API but I don't think it's necessary right now since we have already ways to prevent the race so don't want to add additional complexity with more fine-grained optimization model.

To make the API extend, it reserved an unsigned long as last argument so we could support it in future if someone really needs it.

Q.3 - Why doesn't ptrace work?

Injecting an madvise in the target process using ptrace would not work for us because such injected madvise would have to be executed by the target process, which means that process would have to be runnable and that creates the risk of the abovementioned race and hinting a wrong VMA. Furthermore, we want to act the hint in caller's context, not calle because calle is usually limited in cpuset/cgroups or even freezed state so they can't act by themselves quick enough, which causes more thrashing/kill. It doesn't work if the target process are ptraced(e.g., strace, debugger, minidump) because a process can have at most one ptracer.

[1] https://developer.android.com/topic/performance/memory"
[2] process_getinfo for getting the cookie which is updated whenever
vma of process address layout are changed - Daniel Colascione
- https://lore.kernel.org/lkml/[email protected]/T/#m7694416fd179b2066a2c62b5b139b14e3894e224
[3] anonymous fd which is used for the object(i.e., address range)
validation - Michal Hocko
- https://lore.kernel.org/lkml/[email protected]/

Signed-off-by Minchan Kim <[email protected]>

---
 arch/alpha/kernel/syscalls/syscall.tbl      |  1 +
 arch/arm/tools/syscall.tbl                  |  1 +
 arch/arm64/include/asm/unistd.h             |  2 +-
 arch/arm64/include/asm/unistd32.h           |  2 +
 arch/ia64/kernel/syscalls/syscall.tbl       |  1 +
 arch/m68k/kernel/syscalls/syscall.tbl       |  1 +
 arch/microblaze/kernel/syscalls/syscall.tbl |  1 +
 arch/mips/kernel/syscalls/syscall_n32.tbl   |  1 +
 arch/mips/kernel/syscalls/syscall_n64.tbl   |  1 +
 arch/parisc/kernel/syscalls/syscall.tbl     |  1 +
 arch/powerpc/kernel/syscalls/syscall.tbl    |  1 +
 arch/s390/kernel/syscalls/syscall.tbl       |  1 +
 arch/sh/kernel/syscalls/syscall.tbl         |  1 +
 arch/sparc/kernel/syscalls/syscall.tbl      |  1 +
 arch/x86/entry/syscalls/syscall_32.tbl      |  1 +
 arch/x86/entry/syscalls/syscall_64.tbl      |  1 +
 arch/xtensa/kernel/syscalls/syscall.tbl     |  1 +
 include/linux/syscalls.h                    |  2 +
 include/uapi/asm-generic/unistd.h           |  4 +-
 kernel/sys_ni.c                             |  1 +
 mm/madvise.c                                | 64 +++++++++++++++++++++
 21 files changed, 88 insertions(+), 2 deletions(-)

arch/alpha/kernel/syscalls/syscall.tbl +1 -0

index 36d42da7466a..c82952e6fb80 100644
@@ -477,3 +477,4 @@
 # 545 reserved for clone3
 547	common	openat2				sys_openat2
 548	common	pidfd_getfd			sys_pidfd_getfd
+549	common	process_madvise			sys_process_madvise

arch/arm/tools/syscall.tbl +1 -0

index 4d1cf74a2caa..54c2719fec46 100644
@@ -451,3 +451,4 @@
 435	common	clone3				sys_clone3
 437	common	openat2				sys_openat2
 438	common	pidfd_getfd			sys_pidfd_getfd
+439	common	process_madvise			sys_process_madvise

arch/arm64/include/asm/unistd.h +1 -1

index 1dd22da1c3a9..75f04a1023be 100644
@@ -38,7 +38,7 @@
 #define __ARM_NR_compat_set_tls		(__ARM_NR_COMPAT_BASE + 5)
 #define __ARM_NR_COMPAT_END		(__ARM_NR_COMPAT_BASE + 0x800)
 
-#define __NR_compat_syscalls		439
+#define __NR_compat_syscalls		440
 #endif
 
 #define __ARCH_WANT_SYS_CLONE

arch/arm64/include/asm/unistd32.h +2 -0

index c1c61635f89c..2a27be7a1f91 100644
@@ -883,6 +883,8 @@ __SYSCALL(__NR_clone3, sys_clone3)
 __SYSCALL(__NR_openat2, sys_openat2)
 #define __NR_pidfd_getfd 438
 __SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
+#define __NR_process_madvise 439
+__SYSCALL(__NR_process_madvise, process_madvise)
 
 /*
  * Please add new compat syscalls above this comment and update

arch/ia64/kernel/syscalls/syscall.tbl +1 -0

index 042911e670b8..9524af1c318c 100644
@@ -358,3 +358,4 @@
 # 435 reserved for clone3
 437	common	openat2				sys_openat2
 438	common	pidfd_getfd			sys_pidfd_getfd
+439	common	process_madvise			sys_process_madvise

arch/m68k/kernel/syscalls/syscall.tbl +1 -0

index f4f49fcb76d0..8197050c097c 100644
@@ -437,3 +437,4 @@
 435	common	clone3				__sys_clone3
 437	common	openat2				sys_openat2
 438	common	pidfd_getfd			sys_pidfd_getfd
+439	common	process_madvise			sys_process_madvise

arch/microblaze/kernel/syscalls/syscall.tbl +1 -0

index 4c67b11f9c9e..c5b6c8afe445 100644
@@ -443,3 +443,4 @@
 435	common	clone3				sys_clone3
 437	common	openat2				sys_openat2
 438	common	pidfd_getfd			sys_pidfd_getfd
+439	common	process_madvise			sys_process_madvise

arch/mips/kernel/syscalls/syscall_n32.tbl +1 -0

index 1f9e8ad636cc..8ec8c558aa9c 100644
@@ -376,3 +376,4 @@
 435	n32	clone3				__sys_clone3
 437	n32	openat2				sys_openat2
 438	n32	pidfd_getfd			sys_pidfd_getfd
+439	n32	process_madvise			sys_process_madvise

arch/mips/kernel/syscalls/syscall_n64.tbl +1 -0

index c0b9d802dbf6..0078f891bb92 100644
@@ -352,3 +352,4 @@
 435	n64	clone3				__sys_clone3
 437	n64	openat2				sys_openat2
 438	n64	pidfd_getfd			sys_pidfd_getfd
+439	n64	process_madvise			sys_process_madvise

arch/parisc/kernel/syscalls/syscall.tbl +1 -0

index 52a15f5cd130..09c3b5dc6855 100644
@@ -435,3 +435,4 @@
 435	common	clone3				sys_clone3_wrapper
 437	common	openat2				sys_openat2
 438	common	pidfd_getfd			sys_pidfd_getfd
+439	common	process_madvise			sys_process_madvise

arch/powerpc/kernel/syscalls/syscall.tbl +1 -0

index 35b61bfc1b1a..97eac48c2937 100644
@@ -519,3 +519,4 @@
 435	nospu	clone3				ppc_clone3
 437	common	openat2				sys_openat2
 438	common	pidfd_getfd			sys_pidfd_getfd
+439	common	process_madvise			sys_process_madvise

arch/s390/kernel/syscalls/syscall.tbl +1 -0

index bd7bd3581a0f..8dc8bfd958ea 100644
@@ -440,3 +440,4 @@
 435  common	clone3			sys_clone3			sys_clone3
 437  common	openat2			sys_openat2			sys_openat2
 438  common	pidfd_getfd		sys_pidfd_getfd			sys_pidfd_getfd
+439  common	process_madvise		sys_process_madvise		sys_process_madvise

arch/sh/kernel/syscalls/syscall.tbl +1 -0

index c7a30fcd135f..e69d98040777 100644
@@ -440,3 +440,4 @@
 # 435 reserved for clone3
 437	common	openat2				sys_openat2
 438	common	pidfd_getfd			sys_pidfd_getfd
+439	common	process_madvise			sys_process_madvise

arch/sparc/kernel/syscalls/syscall.tbl +1 -0

index f13615ecdecc..6f6e66dd51f9 100644
@@ -483,3 +483,4 @@
 # 435 reserved for clone3
 437	common	openat2			sys_openat2
 438	common	pidfd_getfd			sys_pidfd_getfd
+439	common	process_madvise			sys_process_madvise

arch/x86/entry/syscalls/syscall_32.tbl +1 -0

index c17cb77eb150..1b2184549e27 100644
@@ -442,3 +442,4 @@
 435	i386	clone3			sys_clone3			__ia32_sys_clone3
 437	i386	openat2			sys_openat2			__ia32_sys_openat2
 438	i386	pidfd_getfd		sys_pidfd_getfd			__ia32_sys_pidfd_getfd
+439	i386	process_madvise		sys_process_madvise		__ia32_sys_process_madvise

arch/x86/entry/syscalls/syscall_64.tbl +1 -0

index 44d510bc9b78..82d60eb1e00d 100644
@@ -359,6 +359,7 @@
 435	common	clone3			__x64_sys_clone3/ptregs
 437	common	openat2			__x64_sys_openat2
 438	common	pidfd_getfd		__x64_sys_pidfd_getfd
+439	common	process_madvise		__x64_sys_process_madvise
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact

arch/xtensa/kernel/syscalls/syscall.tbl +1 -0

index 85a9ab1bc04d..165cae047770 100644
@@ -408,3 +408,4 @@
 435	common	clone3				sys_clone3
 437	common	openat2				sys_openat2
 438	common	pidfd_getfd			sys_pidfd_getfd
+439	common	process_madvise			sys_process_madvise

include/linux/syscalls.h +2 -0

index 1815065d52f3..e4cd2c2f8bb4 100644
@@ -876,6 +876,8 @@ asmlinkage long sys_munlockall(void);
 asmlinkage long sys_mincore(unsigned long start, size_t len,
 				unsigned char __user * vec);
 asmlinkage long sys_madvise(unsigned long start, size_t len, int behavior);
+asmlinkage long sys_process_madvise(int pidfd, unsigned long start,
+			size_t len, int behavior, unsigned long flags);
 asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
 			unsigned long prot, unsigned long pgoff,
 			unsigned long flags);

include/uapi/asm-generic/unistd.h +3 -1

index 3a3201e4618e..85d8c9376a63 100644
@@ -855,9 +855,11 @@ __SYSCALL(__NR_clone3, sys_clone3)
 __SYSCALL(__NR_openat2, sys_openat2)
 #define __NR_pidfd_getfd 438
 __SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
+#define __NR_pidfd_getfd 439
+__SYSCALL(__NR_process_madvise, sys_process_madvise)
 
 #undef __NR_syscalls
-#define __NR_syscalls 439
+#define __NR_syscalls 440
 
 /*
  * 32 bit systems traditionally used different

kernel/sys_ni.c +1 -0

index 3b69a560a7ac..6c7332776e8e 100644
@@ -280,6 +280,7 @@ COND_SYSCALL(mlockall);
 COND_SYSCALL(munlockall);
 COND_SYSCALL(mincore);
 COND_SYSCALL(madvise);
+COND_SYSCALL(process_madvise);
 COND_SYSCALL(remap_file_pages);
 COND_SYSCALL(mbind);
 COND_SYSCALL_COMPAT(mbind);

mm/madvise.c +64 -0

85 lines not on this page · raw message

Signature · 1 line

2.25.0.265.gbab2e86ba0-goog

Minchan Kim

author

2020-02-14 17:06 UTC #8 lore raw

PATCH v5 3/7 mm: check fatal signal pending of target process

In reply to Minchan Kim

Bail out to prevent unnecessary CPU overhead if target process ha pending fatal signal during MADV_COLD| MADV_PAGEOUT operation.

Signed-off-by Minchan Kim <[email protected]>

---
 mm/madvise.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

mm/madvise.c +19 -8

index fadc8d758a46..fca3a9e9bd39 100644
@@ -36,6 +36,7 @@
 struct madvise_walk_private {
 	struct mmu_gather *tlb;
 	bool pageout;
+	struct task_struct *task;
 };
 
 /*

@@ -316,6 +317,9 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 	if (fatal_signal_pending(current))
 		return -EINTR;
 
+	if (fatal_signal_pending(private->task))
+		return -EINTR;
+
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	if (pmd_trans_huge(*pmd)) {
 		pmd_t orig_pmd;

@@ -471,12 +475,14 @@ static const struct mm_walk_ops cold_walk_ops = {
 };
 
 static void madvise_cold_page_range(struct mmu_gather *tlb,
+			     struct task_struct *task,
 			     struct vm_area_struct *vma,
 			     unsigned long addr, unsigned long end)
 {
 	struct madvise_walk_private walk_private = {
 		.pageout = false,
 		.tlb = tlb,
+		.task = task,
 	};
 
 	tlb_start_vma(tlb, vma);

@@ -484,7 +490,8 @@ static void madvise_cold_page_range(struct mmu_gather *tlb,
 	tlb_end_vma(tlb, vma);
 }
 
-static long madvise_cold(struct vm_area_struct *vma,
+static long madvise_cold(struct task_struct *task,
+			struct vm_area_struct *vma,
 			struct vm_area_struct **prev,
 			unsigned long start_addr, unsigned long end_addr)
 {

@@ -497,19 +504,21 @@ static long madvise_cold(struct vm_area_struct *vma,
 
 	lru_add_drain();
 	tlb_gather_mmu(&tlb, mm, start_addr, end_addr);
-	madvise_cold_page_range(&tlb, vma, start_addr, end_addr);
+	madvise_cold_page_range(&tlb, task, vma, start_addr, end_addr);
 	tlb_finish_mmu(&tlb, start_addr, end_addr);
 
 	return 0;
 }
 
 static void madvise_pageout_page_range(struct mmu_gather *tlb,
+			     struct task_struct *task,
 			     struct vm_area_struct *vma,
 			     unsigned long addr, unsigned long end)
 {
 	struct madvise_walk_private walk_private = {
 		.pageout = true,
 		.tlb = tlb,
+		.task = task,
 	};
 
 	tlb_start_vma(tlb, vma);

@@ -533,7 +542,8 @@ static inline bool can_do_pageout(struct vm_area_struct *vma)
 		inode_permission(file_inode(vma->vm_file), MAY_WRITE) == 0;
 }
 
-static long madvise_pageout(struct vm_area_struct *vma,
+static long madvise_pageout(struct task_struct *task,
+			struct vm_area_struct *vma,
 			struct vm_area_struct **prev,
 			unsigned long start_addr, unsigned long end_addr)
 {

@@ -549,7 +559,7 @@ static long madvise_pageout(struct vm_area_struct *vma,
 
 	lru_add_drain();
 	tlb_gather_mmu(&tlb, mm, start_addr, end_addr);
-	madvise_pageout_page_range(&tlb, vma, start_addr, end_addr);
+	madvise_pageout_page_range(&tlb, task, vma, start_addr, end_addr);
 	tlb_finish_mmu(&tlb, start_addr, end_addr);
 
 	return 0;

@@ -929,7 +939,8 @@ static int madvise_inject_error(int behavior,
 #endif
 
 static long
-madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
+madvise_vma(struct task_struct *task, struct vm_area_struct *vma,
+		struct vm_area_struct **prev,
 		unsigned long start, unsigned long end, int behavior)
 {
 	switch (behavior) {

@@ -938,9 +949,9 @@ madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
 	case MADV_WILLNEED:
 		return madvise_willneed(vma, prev, start, end);
 	case MADV_COLD:
-		return madvise_cold(vma, prev, start, end);
+		return madvise_cold(task, vma, prev, start, end);
 	case MADV_PAGEOUT:
-		return madvise_pageout(vma, prev, start, end);
+		return madvise_pageout(task, vma, prev, start, end);
 	case MADV_FREE:
 	case MADV_DONTNEED:
 		return madvise_dontneed_free(vma, prev, start, end, behavior);

@@ -1140,7 +1151,7 @@ int do_madvise(struct task_struct *task, struct mm_struct *mm,
 			tmp = end;
 
 		/* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
-		error = madvise_vma(vma, &prev, start, tmp, behavior);
+		error = madvise_vma(task, vma, &prev, start, tmp, behavior);
 		if (error)
 			goto out;
 		start = tmp;

Signature · 1 line

2.25.0.265.gbab2e86ba0-goog

Minchan Kim

author

2020-02-14 17:06 UTC #9 lore raw

PATCH v5 4/7 pid: export pidfd_get_pid

In reply to Minchan Kim

process_madvise syscall needs pidfd_get_pid function to translate pidfd to pid so this patch exports the function.

Cc Christian Brauner <[email protected]>

Reviewed-by Alexander Duyck <[email protected]>

Signed-off-by Minchan Kim <[email protected]>

---
 include/linux/pid.h |  1 +
 kernel/exit.c       | 17 -----------------
 kernel/pid.c        | 17 +++++++++++++++++
 3 files changed, 18 insertions(+), 17 deletions(-)

include/linux/pid.h +1 -0

index 998ae7d24450..023d9c3a8edc 100644
@@ -75,6 +75,7 @@ extern const struct file_operations pidfd_fops;
 struct file;
 
 extern struct pid *pidfd_pid(const struct file *file);
+extern struct pid *pidfd_get_pid(unsigned int fd);
 
 static inline struct pid *get_pid(struct pid *pid)
 {

kernel/exit.c +0 ~~-17~~

index 0b81b26a872a..43375f9d8bbc 100644
@@ -1470,23 +1470,6 @@ static long do_wait(struct wait_opts *wo)
 	return retval;
 }
 
-static struct pid *pidfd_get_pid(unsigned int fd)
-{
-	struct fd f;
-	struct pid *pid;
-
-	f = fdget(fd);
-	if (!f.file)
-		return ERR_PTR(-EBADF);
-
-	pid = pidfd_pid(f.file);
-	if (!IS_ERR(pid))
-		get_pid(pid);
-
-	fdput(f);
-	return pid;
-}
-
 static long kernel_waitid(int which, pid_t upid, struct waitid_info *infop,
 			  int options, struct rusage *ru)
 {

kernel/pid.c +17 -0

index 0f4ecb57214c..360ba480a2a9 100644
@@ -496,6 +496,23 @@ struct pid *find_ge_pid(int nr, struct pid_namespace *ns)
 	return idr_get_next(&ns->idr, &nr);
 }
 
+struct pid *pidfd_get_pid(unsigned int fd)
+{
+	struct fd f;
+	struct pid *pid;
+
+	f = fdget(fd);
+	if (!f.file)
+		return ERR_PTR(-EBADF);
+
+	pid = pidfd_pid(f.file);
+	if (!IS_ERR(pid))
+		get_pid(pid);
+
+	fdput(f);
+	return pid;
+}
+
 /**
  * pidfd_create() - Create a new pid file descriptor.
  *

Signature · 1 line

2.25.0.265.gbab2e86ba0-goog

Christoph Hellwig

2020-02-17 07:59 UTC #10 lore raw

Re: [PATCH v5 4/7] pid: export pidfd_get_pid

Quoted 2 lines · Minchan Kim

process_madvise syscall needs pidfd_get_pid function to translate pidfd to pid so this patch exports the function.

For that it should not need to exported, but then again the actual patch doesn't export it anyway, so this is just a commit log issue.

Quoted 2 lines

extern struct pid *pidfd_pid(const struct file *file);
+extern struct pid *pidfd_get_pid(unsigned int fd);

... and there is no need for the extern keyword on prototypes in headers.

Minchan Kim

author

2020-02-19 01:02 UTC #11 lore raw

Re: [PATCH v5 4/7] pid: export pidfd_get_pid

Quoted 4 lines · Christoph Hellwig

Quoted 2 lines · Minchan Kim
process_madvise syscall needs pidfd_get_pid function to translate pidfd to pid so this patch exports the function.

Quoted 8 lines

For that it should not need to exported, but then again the actual patch doesn't export it anyway, so this is just a commit log issue.
Quoted 2 lines
extern struct pid *pidfd_pid(const struct file *file);
+extern struct pid *pidfd_get_pid(unsigned int fd);
... and there is no need for the extern keyword on prototypes in headers.

Will fix new version. Thanks for the review!

Minchan Kim

author

2020-02-14 17:06 UTC #12 lore raw

PATCH v5 5/7 mm: support both pid and pidfd for process_madvise

In reply to Minchan Kim

There is a demand[1] to support pid as well pidfd for process_madvise to reduce unnecessary syscall to get pidfd if the user has control of the target process(ie, they could guarantee the process is not gone or pid is not reused. Or, it might be okay to give a hint to wrong process).

This patch aims for supporting both options like waitid(2). So, the syscall is currently,

	int process_madvise(int which, pid_t pid, void *addr,
		size_t length, int advise, unsigned long flag);

@which is actually idtype_t for userspace libray and currently, it supports P_PID and P_PIDFD.

[1] https://lore.kernel.org/linux-mm/[email protected]/

Cc Christian Brauner <[email protected]>

Signed-off-by Minchan Kim <[email protected]>

---
 include/linux/syscalls.h |  3 ++-
 mm/madvise.c             | 34 ++++++++++++++++++++++------------
 2 files changed, 24 insertions(+), 13 deletions(-)

include/linux/syscalls.h +2 -1

index e4cd2c2f8bb4..f5ada20e2943 100644
@@ -876,7 +876,8 @@ asmlinkage long sys_munlockall(void);
 asmlinkage long sys_mincore(unsigned long start, size_t len,
 				unsigned char __user * vec);
 asmlinkage long sys_madvise(unsigned long start, size_t len, int behavior);
-asmlinkage long sys_process_madvise(int pidfd, unsigned long start,
+
+asmlinkage long sys_process_madvise(int which, pid_t pid, unsigned long start,
 			size_t len, int behavior, unsigned long flags);
 asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
 			unsigned long prot, unsigned long pgoff,

mm/madvise.c +22 ~~-12~~

index fca3a9e9bd39..bbbfea93396a 100644
@@ -1180,11 +1180,10 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
 	return do_madvise(current, current->mm, start, len_in, behavior);
 }
 
-SYSCALL_DEFINE5(process_madvise, int, pidfd, unsigned long, start,
+SYSCALL_DEFINE6(process_madvise, int, which, pid_t, upid, unsigned long, start,
 		size_t, len_in, int, behavior, unsigned long, flags)
 {
 	int ret;
-	struct fd f;
 	struct pid *pid;
 	struct task_struct *task;
 	struct mm_struct *mm;

@@ -1195,20 +1194,31 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, unsigned long, start,
 	if (!process_madvise_behavior_valid(behavior))
 		return -EINVAL;
 
-	f = fdget(pidfd);
-	if (!f.file)
-		return -EBADF;
+	switch (which) {
+	case P_PID:
+		if (upid <= 0)
+			return -EINVAL;
+
+		pid = find_get_pid(upid);
+		if (!pid)
+			return -ESRCH;
+		break;
+	case P_PIDFD:
+		if (upid < 0)
+			return -EINVAL;
 
-	pid = pidfd_pid(f.file);
-	if (IS_ERR(pid)) {
-		ret = PTR_ERR(pid);
-		goto fdput;
+		pid = pidfd_get_pid(upid);
+		if (IS_ERR(pid))
+			return PTR_ERR(pid);
+		break;
+	default:
+		return -EINVAL;
 	}
 
 	task = get_pid_task(pid, PIDTYPE_PID);
 	if (!task) {
 		ret = -ESRCH;
-		goto fdput;
+		goto put_pid;
 	}
 
 	mm = mm_access(task, PTRACE_MODE_ATTACH_FSCREDS);

@@ -1221,7 +1231,7 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, unsigned long, start,
 	mmput(mm);
 release_task:
 	put_task_struct(task);
-fdput:
-	fdput(f);
+put_pid:
+	put_pid(pid);
 	return ret;
 }

Signature · 1 line

2.25.0.265.gbab2e86ba0-goog

Minchan Kim

author

2020-02-14 17:06 UTC #13 lore raw

PATCH v5 6/7 mm/madvise: employ mmget_still_valid for write lock

In reply to Minchan Kim

From: Oleksandr Natalenko <[email protected]>

Do the very same trick as we already do since 04f5866e41fb. KSM hints will require locking mmap_sem for write since they modify vm_flags, so for remote KSM hinting this additional check is needed.

Signed-off-by Oleksandr Natalenko <[email protected]>

Signed-off-by Minchan Kim <[email protected]>

---
 mm/madvise.c | 3 +++
 1 file changed, 3 insertions(+)

mm/madvise.c +3 -0

index bbbfea93396a..762a68205e65 100644
@@ -1117,6 +1117,8 @@ int do_madvise(struct task_struct *task, struct mm_struct *mm,
 	if (write) {
 		if (down_write_killable(&mm->mmap_sem))
 			return -EINTR;
+		if (current->mm != mm && !mmget_still_valid(mm))
+			goto skip_mm;
 	} else {
 		down_read(&mm->mmap_sem);
 	}

@@ -1167,6 +1169,7 @@ int do_madvise(struct task_struct *task, struct mm_struct *mm,
 	}
 out:
 	blk_finish_plug(&plug);
+skip_mm:
 	if (write)
 		up_write(&mm->mmap_sem);
 	else

Signature · 1 line

2.25.0.265.gbab2e86ba0-goog

Minchan Kim

author

2020-02-14 17:06 UTC #14 lore raw

PATCH v5 7/7 mm/madvise: allow KSM hints for remote API

In reply to Minchan Kim

From: Oleksandr Natalenko <[email protected]>

It all began with the fact that KSM works only on memory that is marked by madvise(). And the only way to get around that is to either:

* use LD_PRELOAD; or
* patch the kernel with something like UKSM or PKSM.

(i skip ptrace can of worms here intentionally)

To overcome this restriction, lets employ a new remote madvise API. This can be used by some small userspace helper daemon that will do auto-KSM job for us.

I think of two major consumers of remote KSM hints:

* hosts, that run containers, especially similar ones and especially in

    a trusted environment, sharing the same runtime like Node.js;

* heavy applications, that can be run in multiple instances, not limited to opensource ones like Firefox, but also those that cannot be modified since they are binary-only and, maybe, statically linked.

Speaking of statistics, more numbers can be found in the very first submission, that is related to this one [1]. For my current setup with two Firefox instances I get 100 to 200 MiB saved for the second instance depending on the amount of tabs.

1 FF instance with 15 tabs:

   $ echo "$(cat /sys/kernel/mm/ksm/pages_sharing) * 4 / 1024" | bc
   410

2 FF instances, second one has 12 tabs (all the tabs are different):

   $ echo "$(cat /sys/kernel/mm/ksm/pages_sharing) * 4 / 1024" | bc
   592

At the very moment I do not have specific numbers for containerised workload, but those should be comparable in case the containers share similar/same runtime.

[1] https://lore.kernel.org/patchwork/patch/1012142/

Reviewed-by SeongJae Park <[email protected]>

Signed-off-by Oleksandr Natalenko <[email protected]>

Signed-off-by Minchan Kim <[email protected]>

---
 mm/madvise.c | 4 ++++
 1 file changed, 4 insertions(+)

mm/madvise.c +4 -0

index 762a68205e65..0ecacfe93166 100644
@@ -1004,6 +1004,10 @@ process_madvise_behavior_valid(int behavior)
 	switch (behavior) {
 	case MADV_COLD:
 	case MADV_PAGEOUT:
+#ifdef CONFIG_KSM
+	case MADV_MERGEABLE:
+	case MADV_UNMERGEABLE:
+#endif
 		return true;
 	default:
 		return false;

Signature · 1 line

2.25.0.265.gbab2e86ba0-goog