[PATCH 2/2] btrfs: do not flush zlib buffer after every input page

From: Danielle Church <dchurch@cheri.shyou.org>
To: linux-btrfs@vger.kernel.org
Subject: [PATCH 2/2] btrfs: do not flush zlib buffer after every input page
Date: Sat, 3 Jan 2015 22:49:27 -0500 (EST)	[thread overview]
Message-ID: <alpine.LNX.2.00.1501032237360.30995@cheri.shyou.org> (raw)
In-Reply-To: <alpine.LNX.2.00.1501032236270.30995@cheri.shyou.org>

Moving the Z_FINISH into the loop also means we don't have to force a 
flush after every input page to guarantee that there won't be more than 4 
KiB to write at the end.  This patch lets zlib decide when to flush 
buffer, which offers a very moderate space savings (on my system, my 400MB 
test logfile goes from an 11.9% compression ratio to 11.2%, which is 
nothing to write home about) and might offer a similarly-slight 
performance boost.

Since the end result is still a valid zlib stream, it is completely 
backwards-compatible with the existing method.

Signed-off-by: Danielle Church <dchurch@cheri.shyou.org>
---
  fs/btrfs/zlib.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/zlib.c b/fs/btrfs/zlib.c
index 1dc0455..df7d957 100644
--- a/fs/btrfs/zlib.c
+++ b/fs/btrfs/zlib.c
@@ -89,7 +89,7 @@ static int zlib_compress_pages(struct list_head *ws,
  	struct page *in_page = NULL;
  	struct page *out_page = NULL;
  	unsigned long bytes_left;
-	int deflate_flush = Z_SYNC_FLUSH;
+	int deflate_flush = Z_NO_FLUSH;

  	*out_pages = 0;
  	*total_out = 0;
-- 
2.2.1
