[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@taobao.com>
Reviewed-by: Lukas Czerner <lczerner@redhat.com>
Reviewed-by: Eric Gouriou <egouriou@google.com>
---
 fs/ext4/extents.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

2011/6/29 Robin Dong <hao.bigrat@gmail.com>:
> 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@taobao.com>
> Reviewed-by: Lukas Czerner <lczerner@redhat.com>
> Reviewed-by: Eric Gouriou <egouriou@google.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) {

Ronbin Dong,
  why donnot do this line?
 if ((flags & EXT4_GET_BLOCKS_CREATE) == 0) {
TO
 if (!(flags & EXT4_GET_BLOCKS_CREATE) ) {
?
Acked-by:   LiuQi <lingjiujianke@gmail.com>

>                                /*
> --
> 1.7.1
>
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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 <sanbai@taobao.com>
> Reviewed-by: Lukas Czerner <lczerner@redhat.com>
> Reviewed-by: Eric Gouriou <egouriou@google.com>

Thanks added to the ext4 tree.

						- Ted
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