[PATCH stable 5.4, 4.19, 4.14] Revert "btrfs: compression: don't try to compress if we don't have enough pages"

[PATCH stable 5.4, 4.19, 4.14] Revert "btrfs: compression: don't try to compress if we don't have enough pages"

[David Sterba]

From: Qu Wenruo <wqu@suse.com>

commit 4e9655763b82a91e4c341835bb504a2b1590f984 upstream.

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

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 29552d4f6845..33b8fedab6c6 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -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 (nr_pages > 1 && inode_need_compress(inode, start, end)) {
+	if (inode_need_compress(inode, start, end)) {
 		WARN_ON(pages);
 		pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
 		if (!pages) {
-- 
2.33.0

Re: [PATCH stable 5.4, 4.19, 4.14] Revert "btrfs: compression: don't try to compress if we don't have enough pages"

[Greg KH]

On Thu, Sep 09, 2021 at 02:47:50PM +0200, David Sterba wrote:
> From: Qu Wenruo <wqu@suse.com>
> 
> commit 4e9655763b82a91e4c341835bb504a2b1590f984 upstream.
> 
> 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.net
> 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>
> ---
>  fs/btrfs/inode.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 29552d4f6845..33b8fedab6c6 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -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 (nr_pages > 1 && inode_need_compress(inode, start, end)) {
> +	if (inode_need_compress(inode, start, end)) {
>  		WARN_ON(pages);
>  		pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
>  		if (!pages) {
> -- 
> 2.33.0
> 

All now queued up, thanks.

greg k-h