Re: [PATCH] mm: vmscan: Correctly check if reclaimer should scheduleduring shrink_slab

[Minchan Kim]

On Wed, May 18, 2011 at 1:15 AM, Mel Gorman <mgorman@xxxxxxx> wrote:
> It has been reported on some laptops that kswapd is consuming large
> amounts of CPU and not being scheduled when SLUB is enabled during
> large amounts of file copying. It is expected that this is due to
> kswapd missing every cond_resched() point because;
>
> shrink_page_list() calls cond_resched() if inactive pages were isolated
> Â Â Â Âwhich in turn may not happen if all_unreclaimable is set in
> Â Â Â Âshrink_zones(). If for whatver reason, all_unreclaimable is
> Â Â Â Âset on all zones, we can miss calling cond_resched().
>
> balance_pgdat() only calls cond_resched if the zones are not
> Â Â Â Âbalanced. For a high-order allocation that is balanced, it
> Â Â Â Âchecks order-0 again. During that window, order-0 might have
> Â Â Â Âbecome unbalanced so it loops again for order-0 and returns
> Â Â Â Âthat it was reclaiming for order-0 to kswapd(). It can then
> Â Â Â Âfind that a caller has rewoken kswapd for a high-order and
> Â Â Â Âre-enters balance_pgdat() without ever calling cond_resched().
>
> shrink_slab only calls cond_resched() if we are reclaiming slab
> Â Â Â Âpages. If there are a large number of direct reclaimers, the
> Â Â Â Âshrinker_rwsem can be contended and prevent kswapd calling
> Â Â Â Âcond_resched().
>
> This patch modifies the shrink_slab() case. If the semaphore is
> contended, the caller will still check cond_resched(). After each
> successful call into a shrinker, the check for cond_resched() is
> still necessary in case one shrinker call is particularly slow.
>
> This patch replaces
> mm-vmscan-if-kswapd-has-been-running-too-long-allow-it-to-sleep.patch
> in -mm.
>
> [mgorman@xxxxxxx: Preserve call to cond_resched after each call into shrinker]
> From: Minchan Kim <minchan.kim@xxxxxxxxx>
Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>

-- 
Kind regards,
Minchan Kim
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