From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: david@fromorbit.com
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, xfs@oss.sgi.com
Subject: Re: [PATCH 02/12] vmscan: shrinker->nr updates race and go wrong
Date: Mon, 20 Jun 2011 09:46:54 +0900 [thread overview]
Message-ID: <4DFE987E.1070900@jp.fujitsu.com> (raw)
In-Reply-To: <1306998067-27659-3-git-send-email-david@fromorbit.com>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 48e3fbd..dce2767 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -251,17 +251,29 @@ unsigned long shrink_slab(struct shrink_control *shrink,
> unsigned long total_scan;
> unsigned long max_pass;
> int shrink_ret = 0;
> + long nr;
> + long new_nr;
>
> + /*
> + * copy the current shrinker scan count into a local variable
> + * and zero it so that other concurrent shrinker invocations
> + * don't also do this scanning work.
> + */
> + do {
> + nr = shrinker->nr;
> + } while (cmpxchg(&shrinker->nr, nr, 0) != nr);
> +
> + total_scan = nr;
> max_pass = do_shrinker_shrink(shrinker, shrink, 0);
> delta = (4 * nr_pages_scanned) / shrinker->seeks;
> delta *= max_pass;
> do_div(delta, lru_pages + 1);
> - shrinker->nr += delta;
> - if (shrinker->nr < 0) {
> + total_scan += delta;
> + if (total_scan < 0) {
> printk(KERN_ERR "shrink_slab: %pF negative objects to "
> "delete nr=%ld\n",
> - shrinker->shrink, shrinker->nr);
> - shrinker->nr = max_pass;
> + shrinker->shrink, total_scan);
> + total_scan = max_pass;
> }
>
> /*
> @@ -269,13 +281,11 @@ unsigned long shrink_slab(struct shrink_control *shrink,
> * never try to free more than twice the estimate number of
> * freeable entries.
> */
> - if (shrinker->nr > max_pass * 2)
> - shrinker->nr = max_pass * 2;
> + if (total_scan > max_pass * 2)
> + total_scan = max_pass * 2;
>
> - total_scan = shrinker->nr;
> - shrinker->nr = 0;
>
> - trace_mm_shrink_slab_start(shrinker, shrink, nr_pages_scanned,
> + trace_mm_shrink_slab_start(shrinker, shrink, nr, nr_pages_scanned,
> lru_pages, max_pass, delta, total_scan);
>
> while (total_scan >= SHRINK_BATCH) {
> @@ -295,8 +305,19 @@ unsigned long shrink_slab(struct shrink_control *shrink,
> cond_resched();
> }
>
> - shrinker->nr += total_scan;
> - trace_mm_shrink_slab_end(shrinker, shrink_ret, total_scan);
> + /*
> + * move the unused scan count back into the shrinker in a
> + * manner that handles concurrent updates. If we exhausted the
> + * scan, there is no need to do an update.
> + */
> + do {
> + nr = shrinker->nr;
> + new_nr = total_scan + nr;
> + if (total_scan <= 0)
> + break;
> + } while (cmpxchg(&shrinker->nr, nr, new_nr) != nr);
> +
> + trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);
> }
> up_read(&shrinker_rwsem);
> out:
Looks great fix. Please remove tracepoint change from this patch and send it
to -stable. iow, I expect I'll ack your next spin.
thanks.
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next prev parent reply other threads:[~2011-06-20 0:47 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-02 7:00 [PATCH 0/12] Per superblock cache reclaim Dave Chinner
2011-06-02 7:00 ` [PATCH 01/12] vmscan: add shrink_slab tracepoints Dave Chinner
2011-06-20 0:44 ` KOSAKI Motohiro
2011-06-20 0:53 ` Dave Chinner
2011-06-02 7:00 ` [PATCH 02/12] vmscan: shrinker->nr updates race and go wrong Dave Chinner
2011-06-20 0:46 ` KOSAKI Motohiro [this message]
2011-06-20 1:25 ` Dave Chinner
2011-06-20 4:30 ` KOSAKI Motohiro
2011-06-02 7:00 ` [PATCH 03/12] vmscan: reduce wind up shrinker->nr when shrinker can't do work Dave Chinner
2011-06-20 0:51 ` KOSAKI Motohiro
2011-06-21 5:09 ` Dave Chinner
2011-06-21 5:27 ` KOSAKI Motohiro
2011-06-02 7:00 ` [PATCH 04/12] vmscan: add customisable shrinker batch size Dave Chinner
2011-06-02 7:01 ` [PATCH 05/12] inode: convert inode_stat.nr_unused to per-cpu counters Dave Chinner
2011-06-02 7:01 ` [PATCH 06/12] inode: Make unused inode LRU per superblock Dave Chinner
2011-06-04 0:25 ` Al Viro
2011-06-04 1:40 ` Dave Chinner
2011-06-02 7:01 ` [PATCH 07/12] inode: move to per-sb LRU locks Dave Chinner
2011-06-02 7:01 ` [PATCH 08/12] superblock: introduce per-sb cache shrinker infrastructure Dave Chinner
2011-06-04 0:42 ` Al Viro
2011-06-04 1:52 ` Dave Chinner
2011-06-04 14:08 ` Christoph Hellwig
2011-06-04 14:19 ` Al Viro
2011-06-04 14:24 ` Al Viro
2011-06-02 7:01 ` [PATCH 09/12] inode: remove iprune_sem Dave Chinner
2011-06-02 7:01 ` [PATCH 10/12] superblock: add filesystem shrinker operations Dave Chinner
2011-06-02 7:01 ` [PATCH 11/12] vfs: increase shrinker batch size Dave Chinner
2011-06-02 9:30 ` Nicolas Kaiser
2011-06-02 7:01 ` [PATCH 12/12] xfs: make use of new shrinker callout for the inode cache Dave Chinner
2011-06-16 11:33 ` [PATCH 0/12] Per superblock cache reclaim Christoph Hellwig
2011-06-17 3:35 ` KOSAKI Motohiro
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