[PATCH 6/6] XFS: remove congestion_wait() loop from xfs_buf_alloc_pages()

NeilBrown
2021-09-14T00:28:47Z

Documentation commment in gfp.h discourages indefinite retry loops on
ENOMEM and says of __GFP_NOFAIL that it

is definitely preferable to use the flag rather than opencode
endless loop around allocator.

congestion_wait() is indistinguishable from
schedule_timeout_uninterruptible() in practice and it is not a good way
to wait for memory to become available.

So instead of waiting, allocate a single page using __GFP_NOFAIL, then
loop around and try to get any more pages that might be needed with a
bulk allocation. This single-page allocation will wait in the most
appropriate way.

Signed-off-by: NeilBrown <neilb@suse.de>
---
fs/xfs/xfs_buf.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 5fa6cd947dd4..1ae3768f6504 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -372,8 +372,8 @@ xfs_buf_alloc_pages(

/*
* Bulk filling of pages can take multiple calls. Not filling the entire
- * array is not an allocation failure, so don't back off if we get at
- * least one extra page.
+ * array is not an allocation failure, so don't fail or fall back on
+ * __GFP_NOFAIL if we get at least one extra page.
*/
for (;;) {
long last = filled;
@@ -394,7 +394,7 @@ xfs_buf_alloc_pages(
}

XFS_STATS_INC(bp->b_mount, xb_page_retries);
- congestion_wait(BLK_RW_ASYNC, HZ / 50);
+ bp->b_pages[filled++] = alloc_page(gfp_mask | __GFP_NOFAIL);
}
return 0;
}