linux-kernel - Re: [PATCH v5 9/9] binder: use per-vma lock in page reclaiming

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Message-ID: <CAJuCfpHdYPf-WgheBSCK6Md1WakEy_XCiPrw6xTFmPHr7TgnqA@mail.gmail.com>
Date: Tue, 26 Nov 2024 10:46:03 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Carlos Llamas <cmllamas@...gle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Arve Hjønnevåg <arve@...roid.com>, 
	Todd Kjos <tkjos@...roid.com>, Martijn Coenen <maco@...roid.com>, 
	Joel Fernandes <joel@...lfernandes.org>, Christian Brauner <brauner@...nel.org>, 
	linux-kernel@...r.kernel.org, kernel-team@...roid.com, 
	"Liam R. Howlett" <Liam.Howlett@...cle.com>
Subject: Re: [PATCH v5 9/9] binder: use per-vma lock in page reclaiming

On Tue, Nov 26, 2024 at 10:45 AM Suren Baghdasaryan <surenb@...gle.com> wrote:
>
> On Tue, Nov 26, 2024 at 10:40 AM Carlos Llamas <cmllamas@...gle.com> wrote:
> >
> > Use per-vma locking in the shrinker's callback when reclaiming pages,
> > similar to the page installation logic. This minimizes contention with
> > unrelated vmas improving performance. The mmap_sem is still acquired if
> > the per-vma lock cannot be obtained.
> >
> > Cc: Suren Baghdasaryan <surenb@...gle.com>
> > Suggested-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> > Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>
> > Signed-off-by: Carlos Llamas <cmllamas@...gle.com>
> > ---
> >  drivers/android/binder_alloc.c | 29 ++++++++++++++++++++++-------
> >  1 file changed, 22 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
> > index 339db88c1522..8c10c1a6f459 100644
> > --- a/drivers/android/binder_alloc.c
> > +++ b/drivers/android/binder_alloc.c
> > @@ -1128,19 +1128,28 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
> >         struct mm_struct *mm = alloc->mm;
> >         struct vm_area_struct *vma;
> >         unsigned long page_addr;
> > +       int mm_locked = 0;
> >         size_t index;
> >
> >         if (!mmget_not_zero(mm))
> >                 goto err_mmget;
> > -       if (!mmap_read_trylock(mm))
> > -               goto err_mmap_read_lock_failed;
> > -       if (!mutex_trylock(&alloc->mutex))
> > -               goto err_get_alloc_mutex_failed;
> >
> >         index = page->index;
> >         page_addr = alloc->vm_start + index * PAGE_SIZE;
> >
> > -       vma = vma_lookup(mm, page_addr);
> > +       /* attempt per-vma lock first */
> > +       vma = lock_vma_under_rcu(mm, page_addr);
> > +       if (!vma) {
> > +               /* fall back to mmap_lock */
> > +               if (!mmap_read_trylock(mm))
> > +                       goto err_mmap_read_lock_failed;
> > +               mm_locked = 1;
> > +               vma = vma_lookup(mm, page_addr);
> > +       }
> > +
> > +       if (!mutex_trylock(&alloc->mutex))
> > +               goto err_get_alloc_mutex_failed;
> > +
> >         /* ensure the vma corresponds to the binder mapping */
>
> You did add a clarifying comment I asked for in
> https://lore.kernel.org/all/CAJuCfpESdY4L_sSwiCYVCX+5y1WOuAjLNPw35pEGzTSyoHFYPA@mail.gmail.com/

s/did/did not


>
> >         if (vma && !binder_alloc_is_mapped(alloc))
> >                 goto err_invalid_vma;
> > @@ -1163,7 +1172,10 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
> >         }
> >
> >         mutex_unlock(&alloc->mutex);
> > -       mmap_read_unlock(mm);
> > +       if (mm_locked)
> > +               mmap_read_unlock(mm);
> > +       else
> > +               vma_end_read(vma);
> >         mmput_async(mm);
> >         __free_page(page);
> >
> > @@ -1172,7 +1184,10 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
> >  err_invalid_vma:
> >         mutex_unlock(&alloc->mutex);
> >  err_get_alloc_mutex_failed:
> > -       mmap_read_unlock(mm);
> > +       if (mm_locked)
> > +               mmap_read_unlock(mm);
> > +       else
> > +               vma_end_read(vma);
> >  err_mmap_read_lock_failed:
> >         mmput_async(mm);
> >  err_mmget:
> > --
> > 2.47.0.338.g60cca15819-goog
> >