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

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Message-ID: <BANLkTinTk-2005wzEnLtk=guuOCnFdLBDA@mail.gmail.com>
Date:	Wed, 29 Jun 2011 09:30:57 +0800
From:	Steven Liu <lingjiujianke@...il.com>
To:	Robin Dong <hao.bigrat@...il.com>
Cc:	linux-ext4@...r.kernel.org, Robin Dong <sanbai@...bao.com>
Subject: Re: [PATCH v3] ext4: avoid wasted extent cache lookup if !PUNCH_OUT_EXT

2011/6/29 Robin Dong <hao.bigrat@...il.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@...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) {

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@...il.com>

>                                /*
> --
> 1.7.1
>
> --
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