FAILED: patch "[PATCH] btrfs: compression: don't try to compress if we don't have" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f2165627319ffd33a6217275e5690b1ab5c45763 Mon Sep 17 00:00:00 2001
From: David Sterba <[email protected]>
Date: Mon, 14 Jun 2021 12:45:18 +0200
Subject: [PATCH] btrfs: compression: don't try to compress if we don't have
enough pages

The early check if we should attempt compression does not take into account the number of input pages. It can happen that there's only one page, eg. a tail page after some ranges of the BTRFS_MAX_UNCOMPRESSED have been processed, or an isolated page that won't be converted to an inline extent.

The single page would be compressed but a later check would drop it again because the result size must be at least one block shorter than the input. That can never work with just one page.

index a2494c645681..e6eb20987351 100644
@@ -629,7 +629,7 @@ static noinline int compress_file_range(struct async_chunk *async_chunk)
 	 * inode has not been flagged as nocompress.  This flag can
 	 * change at any time if we discover bad compression ratios.
 	 */
-	if (inode_need_compress(BTRFS_I(inode), start, end)) {
+	if (nr_pages > 1 && inode_need_compress(BTRFS_I(inode), start, end)) {
 		WARN_ON(pages);
 		pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
 		if (!pages) {

Hi Greg,

Here is the backport, will also apply to all branches till 4.14-stable.

--
Regards
Sudip

From 6a9596aacb9cc11149423390ac429f9ab5b30075 Mon Sep 17 00:00:00 2001
From: David Sterba <[email protected]>
Date: Mon, 14 Jun 2021 12:45:18 +0200
Subject: [PATCH] btrfs: compression: don't try to compress if we don't have
enough pages

commit f2165627319ffd33a6217275e5690b1ab5c45763 upstream

The early check if we should attempt compression does not take into account the number of input pages. It can happen that there's only one page, eg. a tail page after some ranges of the BTRFS_MAX_UNCOMPRESSED have been processed, or an isolated page that won't be converted to an inline extent.

The single page would be compressed but a later check would drop it again because the result size must be at least one block shorter than the input. That can never work with just one page.

---
 fs/btrfs/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 64dd702a5448..025b02e9799f 100644
@@ -543,7 +543,7 @@ static noinline int compress_file_range(struct async_chunk *async_chunk)
 	 * inode has not been flagged as nocompress.  This flag can
 	 * change at any time if we discover bad compression ratios.
 	 */
-	if (inode_need_compress(inode, start, end)) {
+	if (nr_pages > 1 && inode_need_compress(inode, start, end)) {
 		WARN_ON(pages);
 		pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
 		if (!pages) {

2.30.2