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Re: [PATCH 3/5] superblock: introduce per-sb cache shrinker infrastructu

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 3/5] superblock: introduce per-sb cache shrinker infrastructure
From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Date: Thu, 27 May 2010 13:32:34 -0700
Cc: linux-kernel@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <1274777588-21494-4-git-send-email-david@xxxxxxxxxxxxx>
References: <1274777588-21494-1-git-send-email-david@xxxxxxxxxxxxx> <1274777588-21494-4-git-send-email-david@xxxxxxxxxxxxx>
On Tue, 25 May 2010 18:53:06 +1000
Dave Chinner <david@xxxxxxxxxxxxx> wrote:

> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> With context based shrinkers, we can implement a per-superblock
> shrinker that shrinks the caches attached to the superblock. We
> currently have global shrinkers for the inode and dentry caches that
> split up into per-superblock operations via a coarse proportioning
> method that does not batch very well.  The global shrinkers also
> have a dependency - dentries pin inodes - so we have to be very
> careful about how we register the global shrinkers so that the
> implicit call order is always correct.
> 
> With a per-sb shrinker callout, we can encode this dependency
> directly into the per-sb shrinker, hence avoiding the need for
> strictly ordering shrinker registrations. We also have no need for
> any proportioning code for the shrinker subsystem already provides
> this functionality across all shrinkers. Allowing the shrinker to
> operate on a single superblock at a time means that we do less
> superblock list traversals and locking and reclaim should batch more
> effectively. This should result in less CPU overhead for reclaim and
> potentially faster reclaim of items from each filesystem.
> 

I go all tingly when a changelog contains the word "should".

OK, it _should_ do X.  But _does_ it actually do X?

>  fs/super.c         |   53 +++++++++++++++++++++
>  include/linux/fs.h |    7 +++
>  4 files changed, 88 insertions(+), 214 deletions(-)
> 
> diff --git a/fs/dcache.c b/fs/dcache.c
> index dba6b6d..d7bd781 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -456,21 +456,16 @@ static void prune_one_dentry(struct dentry * dentry)
>   * which flags are set. This means we don't need to maintain multiple
>   * similar copies of this loop.
>   */
> -static void __shrink_dcache_sb(struct super_block *sb, int *count, int flags)
> +static void __shrink_dcache_sb(struct super_block *sb, int count, int flags)

Forgot to update the kerneldoc description of `count'.


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