2011-06-29 00:58:01

by Robin Dong

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 <[email protected]>
Reviewed-by: Lukas Czerner <[email protected]>
Reviewed-by: Eric Gouriou <[email protected]>
---
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

2011-06-29 01:30:59

by Steven Liu

Subject: Re: [PATCH v3] ext4: avoid wasted extent cache lookup if !PUNCH_OUT_EXT

2011/6/29 Robin Dong <[email protected]>:
> 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 <[email protected]>
> Reviewed-by: Lukas Czerner <[email protected]>
> Reviewed-by: Eric Gouriou <[email protected]>
> ---
> ?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) {

Ronbin Dong,
why donnot do this line?
?if ((flags & EXT4_GET_BLOCKS_CREATE) == 0) {
TO
?if (!(flags & EXT4_GET_BLOCKS_CREATE) ) {
?
Acked-by: LiuQi <[email protected]>

> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?/*
> --
> 1.7.1
>
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2011-07-18 03:29:00

by Theodore Ts'o

Subject: Re: [PATCH v3] ext4: avoid wasted extent cache lookup if !PUNCH_OUT_EXT

On Wed, Jun 29, 2011 at 08:57:51AM +0800, Robin Dong wrote:
> 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 <[email protected]>
> Reviewed-by: Lukas Czerner <[email protected]>
> Reviewed-by: Eric Gouriou <[email protected]>

Thanks added to the ext4 tree.

- Ted