[RFC 2/4] buffer: add alloc_folio_buffers() helper

Pankaj Raghav
2023-04-14T11:08:35Z

Folio version of alloc_page_buffers() helper. This is required to convert
create_page_buffers() to create_folio_buffers() later in the series.

It removes one call to compound_head() compared to alloc_page_buffers().

Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
---
fs/buffer.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 59 insertions(+)

diff --git a/fs/buffer.c b/fs/buffer.c
index 44380ff3a31f..0f9c2127543d 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -900,6 +900,65 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
}
EXPORT_SYMBOL_GPL(alloc_page_buffers);

+/*
+ * Create the appropriate buffers when given a folio for data area and
+ * the size of each buffer.. Use the bh->b_this_page linked list to
+ * follow the buffers created. Return NULL if unable to create more
+ * buffers.
+ *
+ * The retry flag is used to differentiate async IO (paging, swapping)
+ * which may not fail from ordinary buffer allocations.
+ */
+struct buffer_head *alloc_folio_buffers(struct folio *folio, unsigned long size,
+ bool retry)
+{
+ struct buffer_head *bh, *head;
+ gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
+ long offset;
+ struct mem_cgroup *memcg, *old_memcg;
+
+ if (retry)
+ gfp |= __GFP_NOFAIL;
+
+ /* The folio lock pins the memcg */
+ memcg = folio_memcg(folio);
+ old_memcg = set_active_memcg(memcg);
+
+ head = NULL;
+ offset = folio_size(folio);
+ while ((offset -= size) >= 0) {
+ bh = alloc_buffer_head(gfp);
+ if (!bh)
+ goto no_grow;
+
+ bh->b_this_page = head;
+ bh->b_blocknr = -1;
+ head = bh;
+
+ bh->b_size = size;
+
+ /* Link the buffer to its folio */
+ set_bh_folio(bh, folio, offset);
+ }
+out:
+ set_active_memcg(old_memcg);
+ return head;
+/*
+ * In case anything failed, we just free everything we got.
+ */
+no_grow:
+ if (head) {
+ do {
+ bh = head;
+ head = head->b_this_page;
+ free_buffer_head(bh);
+ } while (head);
+ }
+
+ goto out;
+}
+EXPORT_SYMBOL_GPL(alloc_folio_buffers);
+
static inline void
link_dev_buffers(struct page *page, struct buffer_head *head)
{
--
2.34.1