Messages in this thread | | | Date | Thu, 29 Mar 2018 11:01:51 +0900 | From | Minchan Kim <> | Subject | Re: [PATCH v2] ANDROID: binder: change down_write to down_read |
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On Wed, Mar 28, 2018 at 06:59:41PM -0700, Arve Hjønnevåg wrote: > On Wed, Mar 28, 2018 at 6:00 PM, Minchan Kim <minchan@kernel.org> 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 <tkjos@google.com> > > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > > Reviewed-by: Martijn Coenen <maco@android.com> > > Signed-off-by: Minchan Kim <minchan@kernel.org> > > --- > > 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.
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