On Thu, Mar 29, 2018 at 11:37:12AM +0900, Minchan Kim wrote:
> 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: Todd Kjos <tk...@google.com>
> Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
> Cc: Arve Hjønnevåg <a...@android.com>
> Reviewed-by: Martijn Coenen <m...@android.com>
> Signed-off-by: Minchan Kim <minc...@kernel.org>
Sent wrong version. Sorry for that. Please ignore this and take it.
>From 480e992d4a650fb98e1397114d75dea7af8e6d0c Mon Sep 17 00:00:00 2001
From: Minchan Kim <minc...@kernel.org>
Date: Wed, 28 Mar 2018 11:32:42 +0900
Subject: [PATCH v3] ANDROID: binder: change down_write to down_read
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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 <a...@android.com>
Cc: Todd Kjos <tk...@google.com>
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Reviewed-by: Martijn Coenen <m...@android.com>
Signed-off-by: Minchan Kim <minc...@kernel.org>
---
>From v2:
* Fix vma->flag setting - Arve
>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(-)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 764b63a5aade..fe62be7d7113 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -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;
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 5a426c877dfb..4f382d51def1 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -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;
--
2.17.0.rc1.321.gba9d0f2565-goog
