ANDROID: binder: change down_write to down_read

PATCH Superseded Minchan Kim 2 participants 2 messages Mar 29, 2018 Android drivers

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Minchan Kim

author

2018-03-29 06:40 UTC #0 lore raw

PATCH v4 1/1 ANDROID: binder: change down_write to down_read

binder_update_page_range needs down_write of mmap_sem because vm_insert_page need to change vma->vm_flags to VM_MIXEDMAP unless it is set. However, when I profile binder working, it seems every binder buffers should be mapped in advance by binder_mmap. It means we could set VM_MIXEDMAP in bider_mmap time which is already hold a mmap_sem as down_write so binder_update_page_range doesn't need to hold a mmap_sem as down_write.

Android suffers from mmap_sem contention so let's reduce mmap_sem down_write.

Cc Arve Hjønnevåg <[email protected]>

Cc Todd Kjos <[email protected]>

Cc Greg Kroah-Hartman <[email protected]>

Reviewed-by Martijn Coenen <[email protected]>

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

---

Quoted 1 line

From v3:

* Fix typoe

Quoted 1 line

From v2:

* Fix vma->flag setting - Arve

Quoted 1 line

From v1:

* remove WARN_ON_ONCE - Greg
* add reviewed-by - Martijn

Martijn, I took your LGTM of v1 as Reviewed-by. If you don't like it or want to change it to acked-by, please, tell me.

 drivers/android/binder.c       | 3 ++-
 drivers/android/binder_alloc.c | 6 +++---
 2 files changed, 5 insertions(+), 4 deletions(-)

drivers/android/binder.c +2 -1

index 764b63a5aade..fe62be7d7113 100644
@@ -4722,7 +4722,8 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma)
 		failure_string = "bad vm_flags";
 		goto err_bad_arg;
 	}
-	vma->vm_flags = (vma->vm_flags | VM_DONTCOPY) & ~VM_MAYWRITE;
+	vma->vm_flags = (vma->vm_flags | VM_DONTCOPY | VM_MIXEDMAP) &
+							~VM_MAYWRITE;
 	vma->vm_ops = &binder_vm_ops;
 	vma->vm_private_data = proc;

drivers/android/binder_alloc.c +3 -3

index 5a426c877dfb..4f382d51def1 100644
@@ -219,7 +219,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
 		mm = alloc->vma_vm_mm;
 
 	if (mm) {
-		down_write(&mm->mmap_sem);
+		down_read(&mm->mmap_sem);
 		vma = alloc->vma;
 	}

@@ -288,7 +288,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
 		/* vm_insert_page does not seem to increment the refcount */
 	}
 	if (mm) {
-		up_write(&mm->mmap_sem);
+		up_read(&mm->mmap_sem);
 		mmput(mm);
 	}
 	return 0;

@@ -321,7 +321,7 @@ static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
 	}
 err_no_vma:
 	if (mm) {
-		up_write(&mm->mmap_sem);
+		up_read(&mm->mmap_sem);
 		mmput(mm);
 	}
 	return vma ? -ENOMEM : -ESRCH;

Signature · 1 line

2.17.0.rc1.321.gba9d0f2565-goog

Joe Perches

2018-03-29 06:48 UTC #1 lore raw

Quoted 5 lines · Minchan Kim

binder_update_page_range needs down_write of mmap_sem because vm_insert_page need to change vma->vm_flags to VM_MIXEDMAP unless it is set. However, when I profile binder working, it seems every binder buffers should be mapped in advance by binder_mmap. It means we could set VM_MIXEDMAP in bider_mmap time which is

typo trivia: binder_mmap

Quoted 2 lines

already hold a mmap_sem as down_write so binder_update_page_range doesn't need to hold a mmap_sem as down_write.

and style trivia:

drivers/android/binder.c

Quoted 1 line

drivers/android/binder.c +0 -0

[]

drivers/android/binder.c static int binder_mmap(struct file *filp, struct vm_area_struct *vma) · line 4726

Quoted 7 lines

drivers/android/binder.c +2 -1

@@ -4722,7 +4722,8 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma)
 		failure_string = "bad vm_flags";
 		goto err_bad_arg;
 	}
-	vma->vm_flags = (vma->vm_flags | VM_DONTCOPY) & ~VM_MAYWRITE;
+	vma->vm_flags = (vma->vm_flags | VM_DONTCOPY | VM_MIXEDMAP) &
+							~VM_MAYWRITE;

Perhaps this is clearer as

	vma->vm_flags |= VM_DONTCOPY | VM_MIXEDMAP;
	vma->vm_flags &= ~VM_MAYWRITE;