binder: use per-vma lock in page reclaiming

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 <[e-mail]>
Suggested-by: Liam R. Howlett <[e-mail]>
Reviewed-by: Suren Baghdasaryan <[e-mail]>
Signed-off-by: Carlos Llamas <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/android/binder_alloc.c

···
 	struct vm_area_struct *vma;
 	struct page *page_to_free;
 	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 = mdata->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;
+
 	/*
 	 * Since a binder_alloc can only be mapped once, we ensure
 	 * the vma corresponds to this mapping by checking whether
···
 	}
 
 	mutex_unlock(&alloc->mutex);
-	mmap_read_unlock(mm);
+	if (mm_locked)
+		mmap_read_unlock(mm);
+	else
+		vma_end_read(vma);
 	mmput_async(mm);
 	binder_free_page(page_to_free);
 
···
 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: