Re: [PATCH v3] ANDROID: binder: change down_write to down_read

[Minchan Kim]

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 <tkjos@xxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Arve Hjønnevåg <arve@xxxxxxxxxxx>
> Reviewed-by: Martijn Coenen <maco@xxxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>

Sent wrong version. Sorry for that. Please ignore this and take it.