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Old 06-17-2011, 12:17 PM
Herton Ronaldo Krzesinski
 
Default mm: vmscan: correctly check if reclaimer should schedule during shrink_slab

On Fri, Jun 17, 2011 at 11:06:52AM +0100, Colin King wrote:
> From: Minchan Kim <minchan.kim@gmail.com>
>
> 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
> which in turn may not happen if all_unreclaimable is set in
> shrink_zones(). If for whatver reason, all_unreclaimable is
> set on all zones, we can miss calling cond_resched().
>
> balance_pgdat() only calls cond_resched if the zones are not
> balanced. For a high-order allocation that is balanced, it
> checks order-0 again. During that window, order-0 might have
> become unbalanced so it loops again for order-0 and returns
> that it was reclaiming for order-0 to kswapd(). It can then
> find that a caller has rewoken kswapd for a high-order and
> re-enters balance_pgdat() without ever calling cond_resched().
>
> shrink_slab only calls cond_resched() if we are reclaiming slab
> pages. If there are a large number of direct reclaimers, the
> shrinker_rwsem can be contended and prevent kswapd calling
> cond_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() remains in
> case one shrinker is particularly slow.
>
> [mgorman@suse.de: preserve call to cond_resched after each call into shrinker]
> Signed-off-by: Mel Gorman <mgorman@suse.de>
> Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Wu Fengguang <fengguang.wu@intel.com>
> Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
> Tested-by: Colin King <colin.king@canonical.com>
> Cc: Raghavendra D Prabhu <raghu.prabhu13@gmail.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Chris Mason <chris.mason@oracle.com>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Pekka Enberg <penberg@kernel.org>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: <stable@kernel.org> [2.6.38+]
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> ---
> mm/vmscan.c | 9 +++++++--
> 1 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 0665520..648aab8 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -230,8 +230,11 @@ unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
> if (scanned == 0)
> scanned = SWAP_CLUSTER_MAX;
>
> - if (!down_read_trylock(&shrinker_rwsem))
> - return 1; /* Assume we'll be able to shrink next time */
> + if (!down_read_trylock(&shrinker_rwsem)) {
> + /* Assume we'll be able to shrink next time */
> + ret = 1;
> + goto out;
> + }
>
> list_for_each_entry(shrinker, &shrinker_list, list) {
> unsigned long long delta;
> @@ -282,6 +285,8 @@ unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
> shrinker->nr += total_scan;
> }
> up_read(&shrinker_rwsem);
> +out:
> + cond_resched();
> return ret;
> }

Acked-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>

>
> --
> 1.7.0.4
>
>
> --
> kernel-team mailing list
> kernel-team@lists.ubuntu.com
> https://lists.ubuntu.com/mailman/listinfo/kernel-team
>

--
[]'s
Herton

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