linux-ext4 - [PATCH v3] ext4: avoid wasted extent cache lookup if !PUNCH_OUT

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Message-Id: <1309309071-2244-1-git-send-email-sanbai@taobao.com>
Date:	Wed, 29 Jun 2011 08:57:51 +0800
From:	Robin Dong <hao.bigrat@...il.com>
To:	linux-ext4@...r.kernel.org
Cc:	Robin Dong <sanbai@...bao.com>
Subject: [PATCH v3] ext4: avoid wasted extent cache lookup if !PUNCH_OUT_EXT

This patch avoids an extraneous lookup of the extent cache
in ext4_ext_map_blocks() when the flag
EXT4_GET_BLOCKS_PUNCH_OUT_EXT is absent.

The existing logic was performing the lookup but not making
use of the result. The patch simply reverses the order of evaluation
in the condition.

Since ext4_ext_in_cache() does not initialize newex on misses, bypassing
its invocation does not introduce any new issue in this regard.

Signed-off-by: Robin Dong <sanbai@...bao.com>
Reviewed-by: Lukas Czerner <lczerner@...hat.com>
Reviewed-by: Eric Gouriou <egouriou@...gle.com>
---
 fs/ext4/extents.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index eb63c7b..fed2633 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3358,8 +3358,8 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 	trace_ext4_ext_map_blocks_enter(inode, map->m_lblk, map->m_len, flags);
 
 	/* check in cache */
-	if (ext4_ext_in_cache(inode, map->m_lblk, &newex) &&
-		((flags & EXT4_GET_BLOCKS_PUNCH_OUT_EXT) == 0)) {
+	if (!(flags & EXT4_GET_BLOCKS_PUNCH_OUT_EXT) &&
+		ext4_ext_in_cache(inode, map->m_lblk, &newex)) {
 		if (!newex.ee_start_lo && !newex.ee_start_hi) {
 			if ((flags & EXT4_GET_BLOCKS_CREATE) == 0) {
 				/*
-- 
1.7.1

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