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Re: [PATCH 1/2] mm: add context argument to shrinker callback

To: Avi Kivity <avi@xxxxxxxxxx>
Subject: Re: [PATCH 1/2] mm: add context argument to shrinker callback
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 28 Apr 2010 23:45:02 +1000
Cc: linux-kernel@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <4BD80260.3050501@xxxxxxxxxx>
References: <1271118255-21070-1-git-send-email-david@xxxxxxxxxxxxx> <1271118255-21070-2-git-send-email-david@xxxxxxxxxxxxx> <4BD80260.3050501@xxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Wed, Apr 28, 2010 at 12:39:44PM +0300, Avi Kivity wrote:
> On 04/13/2010 03:24 AM, Dave Chinner wrote:
> >From: Dave Chinner<dchinner@xxxxxxxxxx>
> >
> >The current shrinker implementation requires the registered callback
> >to have global state to work from. This makes it difficult to shrink
> >caches that are not global (e.g. per-filesystem caches). Add a
> >context argument to the shrinker callback so that it can easily be
> >used in such situations.
> 
> >@@ -995,7 +995,8 @@ static inline void sync_mm_rss(struct task_struct *task, 
> >struct mm_struct *mm)
> >   * querying the cache size, so a fastpath for that case is appropriate.
> >   */
> >  struct shrinker {
> >-    int (*shrink)(int nr_to_scan, gfp_t gfp_mask);
> >+    int (*shrink)(void *ctx, int nr_to_scan, gfp_t gfp_mask);
> >+    void *ctx;      /* user callback context */
> >     int seeks;      /* seeks to recreate an obj */
> 
> 
> It's nicer (and slightly cheaper) to have
> 
>   int (*shrink)(struct shrinker *shrinker, int nr_to_scan, gfp_t gfp_mask);
>   /* no void *ctx; */
> 
> Clients can use container_of() to reach their context from the
> shrinker argument.

Agreed, that makes a lot of sense. I'll change it for the next version.

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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