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

Carlos Llamas
2024-11-26T18:40:45Z

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@google.com>
Suggested-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Carlos Llamas <cmllamas@google.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 */
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