[PATCH 1/9] fs: make block_read_full_folio() support large folio

From: Zhang Yi
Date: Mon Nov 25 2024 - 07:27:39 EST


From: Zhang Yi <yi.zhang@xxxxxxxxxx>

block_read_full_folio() uses an on-stack array to save the un-uptodated
buffers. This approach is acceptable for small folios, as there are not
too many buffers in a single folio. However, if the folio is a large
folio, the number of buffers could reach up to 2,000 for a 2MB folio
size with a 1KB block size. Therefore, we cannot use the 'arr' array for
large folios, instead, we should iterate through the buffers using 'bh =
bh->b_this_page'.

Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
---
fs/buffer.c | 34 +++++++++++++++++-----------------
1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 1fc9a50def0b..54e608c8912e 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2366,7 +2366,7 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block)
{
struct inode *inode = folio->mapping->host;
sector_t iblock, lblock;
- struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
+ struct buffer_head *bh, *head;
size_t blocksize;
int nr, i;
int fully_mapped = 1;
@@ -2377,8 +2377,6 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block)
if (IS_ENABLED(CONFIG_FS_VERITY) && IS_VERITY(inode))
limit = inode->i_sb->s_maxbytes;

- VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
-
head = folio_create_buffers(folio, inode, 0);
blocksize = head->b_size;

@@ -2416,7 +2414,10 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block)
if (buffer_uptodate(bh))
continue;
}
- arr[nr++] = bh;
+ /* lock the buffer */
+ lock_buffer(bh);
+ mark_buffer_async_read(bh);
+ nr++;
} while (i++, iblock++, (bh = bh->b_this_page) != head);

if (fully_mapped)
@@ -2431,25 +2432,24 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block)
return 0;
}

- /* Stage two: lock the buffers */
- for (i = 0; i < nr; i++) {
- bh = arr[i];
- lock_buffer(bh);
- mark_buffer_async_read(bh);
- }
-
/*
- * Stage 3: start the IO. Check for uptodateness
- * inside the buffer lock in case another process reading
- * the underlying blockdev brought it uptodate (the sct fix).
+ * Start the IO. Check for uptodateness inside the buffer lock
+ * in case another process reading the underlying blockdev brought
+ * it uptodate (the sct fix).
*/
- for (i = 0; i < nr; i++) {
- bh = arr[i];
+ bh = head;
+ do {
+ if (!buffer_async_read(bh))
+ continue;
+
if (buffer_uptodate(bh))
end_buffer_async_read(bh, 1);
else
submit_bh(REQ_OP_READ, bh);
- }
+
+ nr--;
+ } while (nr && (bh = bh->b_this_page) != head);
+
return 0;
}
EXPORT_SYMBOL(block_read_full_folio);
--
2.46.1