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 stable@vger.kernel.org.

thanks,

greg k-h

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

From 4e9655763b82a91e4c341835bb504a2b1590f984 Mon Sep 17 00:00:00 2001

From: Qu Wenruo wqu@suse.com Date: Wed, 25 Aug 2021 13:41:42 +0800 Subject: [PATCH] Revert "btrfs: compression: don't try to compress if we don't have enough pages"

This reverts commit f2165627319ffd33a6217275e5690b1ab5c45763.

[BUG] It's no longer possible to create compressed inline extent after commit f2165627319f ("btrfs: compression: don't try to compress if we don't have enough pages").

[CAUSE] For compression code, there are several possible reasons we have a range that needs to be compressed while it's no more than one page.

- Compressed inline write The data is always smaller than one sector and the test lacks the condition to properly recognize a non-inline extent.

- Compressed subpage write For the incoming subpage compressed write support, we require page alignment of the delalloc range. And for 64K page size, we can compress just one page into smaller sectors.

For those reasons, the requirement for the data to be more than one page is not correct, and is already causing regression for compressed inline data writeback. The idea of skipping one page to avoid wasting CPU time could be revisited in the future.

[FIX] Fix it by reverting the offending commit.

Reported-by: Zygo Blaxell ce3g8jdj@umail.furryterror.org Link: https://lore.kernel.org/linux-btrfs/afa2742.c084f5d6.17b6b08dffc@tnonline.ne... Fixes: f2165627319f ("btrfs: compression: don't try to compress if we don't have enough pages") CC: stable@vger.kernel.org # 4.4+ Signed-off-by: Qu Wenruo wqu@suse.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 06f9f167222b..bd5689fa290e 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -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 (nr_pages > 1 && inode_need_compress(BTRFS_I(inode), start, end)) { + if (inode_need_compress(BTRFS_I(inode), start, end)) { WARN_ON(pages); pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS); if (!pages) {