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mm: move use_mm/unuse_mm from aio.c to mm/

PATCH New Michael S. Tsirkin 1 participant 4 messages Sep 17, 2009 1 message not in the archive

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Michael S. Tsirkin

author maintainer
#1 lore raw

PATCH v3 1/2 mm: move use_mm/unuse_mm from aio.c to mm/

Anyone who wants to do copy to/from user from a kernel thread, needs use_mm (like what fs/aio has). Move that into mm/, to make reusing and exporting easier down the line, and make aio use it. Next intended user, besides aio, will be vhost-net.

Acked-by Andrea Arcangeli <[email protected]>
Signed-off-by Michael S. Tsirkin <[email protected]>
---
 fs/aio.c                    |   47 +------------------------------------
 include/linux/mmu_context.h |    9 +++++++
 mm/Makefile                 |    2 +-
 mm/mmu_context.c            |   55 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 66 insertions(+), 47 deletions(-)
 create mode 100644 include/linux/mmu_context.h
 create mode 100644 mm/mmu_context.c
fs/aio.c +1 -46
index d065b2c..fc21c23 100644
@@ -24,6 +24,7 @@
 #include <linux/file.h>
 #include <linux/mm.h>
 #include <linux/mman.h>
+#include <linux/mmu_context.h>
 #include <linux/slab.h>
 #include <linux/timer.h>
 #include <linux/aio.h>

@@ -34,7 +35,6 @@
 
 #include <asm/kmap_types.h>
 #include <asm/uaccess.h>
-#include <asm/mmu_context.h>
 
 #if DEBUG > 1
 #define dprintk		printk

@@ -595,51 +595,6 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id)
 }
 
 /*
- * use_mm
- *	Makes the calling kernel thread take on the specified
- *	mm context.
- *	Called by the retry thread execute retries within the
- *	iocb issuer's mm context, so that copy_from/to_user
- *	operations work seamlessly for aio.
- *	(Note: this routine is intended to be called only
- *	from a kernel thread context)
- */
-static void use_mm(struct mm_struct *mm)
-{
-	struct mm_struct *active_mm;
-	struct task_struct *tsk = current;
-
-	task_lock(tsk);
-	active_mm = tsk->active_mm;
-	atomic_inc(&mm->mm_count);
-	tsk->mm = mm;
-	tsk->active_mm = mm;
-	switch_mm(active_mm, mm, tsk);
-	task_unlock(tsk);
-
-	mmdrop(active_mm);
-}
-
-/*
- * unuse_mm
- *	Reverses the effect of use_mm, i.e. releases the
- *	specified mm context which was earlier taken on
- *	by the calling kernel thread
- *	(Note: this routine is intended to be called only
- *	from a kernel thread context)
- */
-static void unuse_mm(struct mm_struct *mm)
-{
-	struct task_struct *tsk = current;
-
-	task_lock(tsk);
-	tsk->mm = NULL;
-	/* active_mm is still 'mm' */
-	enter_lazy_tlb(mm, tsk);
-	task_unlock(tsk);
-}
-
-/*
  * Queue up a kiocb to be retried. Assumes that the kiocb
  * has already been marked as kicked, and places it on
  * the retry run list for the corresponding ioctx, if it
include/linux/mmu_context.h new file +9 -0
new file mode 100644
index 0000000..70fffeb
@@ -0,0 +1,9 @@
+#ifndef _LINUX_MMU_CONTEXT_H
+#define _LINUX_MMU_CONTEXT_H
+
+struct mm_struct;
+
+void use_mm(struct mm_struct *mm);
+void unuse_mm(struct mm_struct *mm);
+
+#endif
mm/Makefile +1 -1
index 5e0bd64..46c3892 100644
@@ -11,7 +11,7 @@ obj-y			:= bootmem.o filemap.o mempool.o oom_kill.o fadvise.o \
 			   maccess.o page_alloc.o page-writeback.o pdflush.o \
 			   readahead.o swap.o truncate.o vmscan.o shmem.o \
 			   prio_tree.o util.o mmzone.o vmstat.o backing-dev.o \
-			   page_isolation.o mm_init.o $(mmu-y)
+			   page_isolation.o mm_init.o mmu_context.o $(mmu-y)
 obj-y += init-mm.o
 
 obj-$(CONFIG_PROC_PAGE_MONITOR) += pagewalk.o
mm/mmu_context.c new file +55 -0

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author maintainer
#2 lore raw

PATCH v3 1/2 mm: move use_mm/unuse_mm from aio.c to mm/

In reply to a message not in the archive

Anyone who wants to do copy to/from user from a kernel thread, needs use_mm (like what fs/aio has). Move that into mm/, to make reusing and exporting easier down the line, and make aio use it. Next intended user, besides aio, will be vhost-net.

Acked-by Andrea Arcangeli <[email protected]>
Signed-off-by Michael S. Tsirkin <[email protected]>
---
 fs/aio.c                    |   47 +------------------------------------
 include/linux/mmu_context.h |    9 +++++++
 mm/Makefile                 |    2 +-
 mm/mmu_context.c            |   55 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 66 insertions(+), 47 deletions(-)
 create mode 100644 include/linux/mmu_context.h
 create mode 100644 mm/mmu_context.c
fs/aio.c +1 -46
index d065b2c..fc21c23 100644
@@ -24,6 +24,7 @@
 #include <linux/file.h>
 #include <linux/mm.h>
 #include <linux/mman.h>
+#include <linux/mmu_context.h>
 #include <linux/slab.h>
 #include <linux/timer.h>
 #include <linux/aio.h>

@@ -34,7 +35,6 @@
 
 #include <asm/kmap_types.h>
 #include <asm/uaccess.h>
-#include <asm/mmu_context.h>
 
 #if DEBUG > 1
 #define dprintk		printk

@@ -595,51 +595,6 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id)
 }
 
 /*
- * use_mm
- *	Makes the calling kernel thread take on the specified
- *	mm context.
- *	Called by the retry thread execute retries within the
- *	iocb issuer's mm context, so that copy_from/to_user
- *	operations work seamlessly for aio.
- *	(Note: this routine is intended to be called only
- *	from a kernel thread context)
- */
-static void use_mm(struct mm_struct *mm)
-{
-	struct mm_struct *active_mm;
-	struct task_struct *tsk = current;
-
-	task_lock(tsk);
-	active_mm = tsk->active_mm;
-	atomic_inc(&mm->mm_count);
-	tsk->mm = mm;
-	tsk->active_mm = mm;
-	switch_mm(active_mm, mm, tsk);
-	task_unlock(tsk);
-
-	mmdrop(active_mm);
-}
-
-/*
- * unuse_mm
- *	Reverses the effect of use_mm, i.e. releases the
- *	specified mm context which was earlier taken on
- *	by the calling kernel thread
- *	(Note: this routine is intended to be called only
- *	from a kernel thread context)
- */
-static void unuse_mm(struct mm_struct *mm)
-{
-	struct task_struct *tsk = current;
-
-	task_lock(tsk);
-	tsk->mm = NULL;
-	/* active_mm is still 'mm' */
-	enter_lazy_tlb(mm, tsk);
-	task_unlock(tsk);
-}
-
-/*
  * Queue up a kiocb to be retried. Assumes that the kiocb
  * has already been marked as kicked, and places it on
  * the retry run list for the corresponding ioctx, if it
include/linux/mmu_context.h new file +9 -0
new file mode 100644
index 0000000..70fffeb
@@ -0,0 +1,9 @@
+#ifndef _LINUX_MMU_CONTEXT_H
+#define _LINUX_MMU_CONTEXT_H
+
+struct mm_struct;
+
+void use_mm(struct mm_struct *mm);
+void unuse_mm(struct mm_struct *mm);
+
+#endif
mm/Makefile +1 -1
index 5e0bd64..46c3892 100644
@@ -11,7 +11,7 @@ obj-y			:= bootmem.o filemap.o mempool.o oom_kill.o fadvise.o \
 			   maccess.o page_alloc.o page-writeback.o pdflush.o \
 			   readahead.o swap.o truncate.o vmscan.o shmem.o \
 			   prio_tree.o util.o mmzone.o vmstat.o backing-dev.o \
-			   page_isolation.o mm_init.o $(mmu-y)
+			   page_isolation.o mm_init.o mmu_context.o $(mmu-y)
 obj-y += init-mm.o
 
 obj-$(CONFIG_PROC_PAGE_MONITOR) += pagewalk.o
mm/mmu_context.c new file +55 -0

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Signature · 1 line
1.6.2.5
author maintainer
#3 lore raw

PATCH v3 2/2 mm: reduce atomic use on use_mm fast path

In reply to a message not in the archive

When mm switched to matches that of active mm, we don't need to increment and then drop the mm count. In a simple benchmark this happens in about 50% of time. Making that conditional reduces contention on that cache line on SMP systems.

Acked-by Andrea Arcangeli <[email protected]>
Signed-off-by Michael S. Tsirkin <[email protected]>
---
 mm/mmu_context.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)
mm/mmu_context.c +6 -3
index fd473b5..ded9081 100644
@@ -26,13 +26,16 @@ void use_mm(struct mm_struct *mm)
 
 	task_lock(tsk);
 	active_mm = tsk->active_mm;
-	atomic_inc(&mm->mm_count);
+	if (active_mm != mm) {
+		atomic_inc(&mm->mm_count);
+		tsk->active_mm = mm;
+	}
 	tsk->mm = mm;
-	tsk->active_mm = mm;
 	switch_mm(active_mm, mm, tsk);
 	task_unlock(tsk);
 
-	mmdrop(active_mm);
+	if (active_mm != mm)
+		mmdrop(active_mm);
 }
 
 /*
Signature · 7 lines
1.6.2.5

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to [email protected].  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"[email protected]"> [email protected] </a>
author maintainer
#4 lore raw

PATCH v3 2/2 mm: reduce atomic use on use_mm fast path

In reply to a message not in the archive

When mm switched to matches that of active mm, we don't need to increment and then drop the mm count. In a simple benchmark this happens in about 50% of time. Making that conditional reduces contention on that cache line on SMP systems.

Acked-by Andrea Arcangeli <[email protected]>
Signed-off-by Michael S. Tsirkin <[email protected]>
---
 mm/mmu_context.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)
mm/mmu_context.c +6 -3
index fd473b5..ded9081 100644
@@ -26,13 +26,16 @@ void use_mm(struct mm_struct *mm)
 
 	task_lock(tsk);
 	active_mm = tsk->active_mm;
-	atomic_inc(&mm->mm_count);
+	if (active_mm != mm) {
+		atomic_inc(&mm->mm_count);
+		tsk->active_mm = mm;
+	}
 	tsk->mm = mm;
-	tsk->active_mm = mm;
 	switch_mm(active_mm, mm, tsk);
 	task_unlock(tsk);
 
-	mmdrop(active_mm);
+	if (active_mm != mm)
+		mmdrop(active_mm);
 }
 
 /*
Signature · 1 line
1.6.2.5