[PATCH 2/2] btrfs: Allocate page arrays using bulk page allocator.

Sweet Tea Dorminy
2022-03-28T20:14:43Z

While calling alloc_page() in a loop is an effective way to populate an
array of pages, the kernel provides a method to allocate pages in bulk.
alloc_pages_bulk_array() populates the NULL slots in a page array, trying to
grab more than one page at a time.

Unfortunately, it doesn't guarantee allocating all slots in the array,
but it's easy to call it in a loop and return an error if no progress
occurs. Similar code can be found in xfs/xfs_buf.c:xfs_buf_alloc_pages().

Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
---
fs/btrfs/ctree.c | 25 ++++++++++++++++---------
1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 4e81e75c8e7c..37711a66e726 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -102,17 +102,24 @@ void btrfs_free_path(struct btrfs_path *p)
*/
int btrfs_alloc_page_array(unsigned long nr_pages, struct page **page_array)
{
- int i;
- for (i = 0; i < nr_pages; i++) {
- struct page *page;
- if (page_array[i])
+ long allocated = 0;
+ for (;;) {
+ long last = allocated;
+
+ allocated = alloc_pages_bulk_array(GFP_NOFS, nr_pages,
+ page_array);
+ if (allocated == nr_pages)
+ return 0;
+
+ if (allocated != last)
continue;
- page = alloc_page(GFP_NOFS);
- if (!page)
- return -ENOMEM;
- page_array[i] = page;
+ /*
+ * During this iteration, no page could be allocated, even
+ * though alloc_pages_bulk_array() falls back to alloc_page()
+ * if it could not bulk-allocate. So we must be out of memory.
+ */
+ return -ENOMEM;
}
- return 0;
}

/*
--
2.35.1