2018-03-29 01:01:59

by Minchan Kim

Subject: [PATCH v2] 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: Todd Kjos <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Reviewed-by: Martijn Coenen <[email protected]>
Signed-off-by: Minchan Kim <[email protected]>
---
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 | 2 +-
drivers/android/binder_alloc.c | 6 +++---
2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 764b63a5aade..9a14c6dd60c4 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -4722,7 +4722,7 @@ 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 |= (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

2018-03-29 02:00:53

by Arve Hjønnevåg

Subject: Re: [PATCH v2] ANDROID: binder: change down_write to down_read

On Wed, Mar 28, 2018 at 6:00 PM, Minchan Kim <[email protected]> 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 <[email protected]>
> Cc: Greg Kroah-Hartman <[email protected]>
> Reviewed-by: Martijn Coenen <[email protected]>
> Signed-off-by: Minchan Kim <[email protected]>
> ---
> 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 | 2 +-
> drivers/android/binder_alloc.c | 6 +++---
> 2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index 764b63a5aade..9a14c6dd60c4 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -4722,7 +4722,7 @@ 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 |= (VM_DONTCOPY | VM_MIXEDMAP) & ~VM_MAYWRITE;

Why did you change this to |=? You are no longer clearing 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
>



--
Arve Hjønnevåg

2018-03-29 02:03:35

by Minchan Kim

Subject: Re: [PATCH v2] ANDROID: binder: change down_write to down_read

On Wed, Mar 28, 2018 at 06:59:41PM -0700, Arve Hj?nnev?g wrote:
> On Wed, Mar 28, 2018 at 6:00 PM, Minchan Kim <[email protected]> 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 <[email protected]>
> > Cc: Greg Kroah-Hartman <[email protected]>
> > Reviewed-by: Martijn Coenen <[email protected]>
> > Signed-off-by: Minchan Kim <[email protected]>
> > ---
> > 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 | 2 +-
> > drivers/android/binder_alloc.c | 6 +++---
> > 2 files changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> > index 764b63a5aade..9a14c6dd60c4 100644
> > --- a/drivers/android/binder.c
> > +++ b/drivers/android/binder.c
> > @@ -4722,7 +4722,7 @@ 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 |= (VM_DONTCOPY | VM_MIXEDMAP) & ~VM_MAYWRITE;
>
> Why did you change this to |=? You are no longer clearing VM_MAYWRITE.

Oops, Thanks for pointing out.
I will respin.