linux-kernel - Re: [PATCH] remove duplicating priority setting in try_to_free

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Message-Id: <20080127213312.517b8014.akpm@linux-foundation.org>
Date:	Sun, 27 Jan 2008 21:33:12 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"minchan kim" <minchan.kim@...il.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Martin Bligh <mbligh@...igh.org>,
	Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: [PATCH] remove duplicating priority setting in try_to_free_p

On Sat, 26 Jan 2008 02:29:23 -0500 "minchan kim" <minchan.kim@...il.com> wrote:

> shrink_zones in try_to_free_pages already set zone through
> note_zone_scanning_priority.
> So, setting prev_priority in try_to_free_pages is needless.
> 
> This patch is made by 2.6.24-rc8.
> 
> Signed-off-by: barrios <minchan.kim@...il.com>
> ---
>  mm/vmscan.c |   17 -----------------
>  1 files changed, 0 insertions(+), 17 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index e5a9597..fc55c23 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1273,23 +1273,6 @@ unsigned long try_to_free_pages(struct z
>     if (!sc.all_unreclaimable)
>         ret = 1;
>  out:
> -   /*
> -    * Now that we've scanned all the zones at this priority level, note
> -    * that level within the zone so that the next thread which performs
> -    * scanning of this zone will immediately start out at this priority
> -    * level.  This affects only the decision whether or not to bring
> -    * mapped pages onto the inactive list.
> -    */
> -   if (priority < 0)
> -       priority = 0;
> -   for (i = 0; zones[i] != NULL; i++) {
> -       struct zone *zone = zones[i];
> -
> -       if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
> -           continue;
> -
> -       zone->prev_priority = priority;
> -   }
>     return ret;
>  }

(your mail client is replacing tabs with spaces)

I think this is actually a bugfix.  The code you're removing doesn't do the 

	if (priority < zone->prev_priority)

thing.

otoh with this change, the only thing which will cause prev_priority to
increase (ie: lower priority) is kswapd, which seems odd.

So:

a) this is a functional change and needs more thought and lots of runtime
   testing.  I'll duck it for now.

b) the prev_priority stuff is still screwed up.
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