From: Andrew Morton <akpm@linux-foundation.org>
To: Mel Gorman <mel@csn.ul.ie>
Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
Linux Kernel List <linux-kernel@vger.kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Minchan Kim <minchan.kim@gmail.com>,
Wu Fengguang <fengguang.wu@intel.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Subject: Re: [PATCH 8/8] writeback: Do not sleep on the congestion queue if there are no congested BDIs or if significant congestion is not being encountered in the current zone
Date: Thu, 16 Sep 2010 15:28:10 -0700 [thread overview]
Message-ID: <20100916152810.cb074e9f.akpm@linux-foundation.org> (raw)
In-Reply-To: <1284553671-31574-9-git-send-email-mel@csn.ul.ie>
On Wed, 15 Sep 2010 13:27:51 +0100
Mel Gorman <mel@csn.ul.ie> wrote:
> If wait_iff_congested() is called with no BDI congested, the function simply
> calls cond_resched(). In the event there is significant writeback happening
> in the zone that is being reclaimed, this can be a poor decision as reclaim
> would succeed once writeback was completed. Without any backoff logic,
> younger clean pages can be reclaimed resulting in more reclaim overall and
> poor performance.
This is because cond_resched() is a no-op, and we skip around the
under-writeback pages and go off and look further along the LRU for
younger clean pages, yes?
> This patch tracks how many pages backed by a congested BDI were found during
> scanning. If all the dirty pages encountered on a list isolated from the
> LRU belong to a congested BDI, the zone is marked congested until the zone
> reaches the high watermark.
High watermark, or low watermark?
The terms are rather ambiguous so let's avoid them. Maybe "full"
watermark and "empty"?
>
> ...
>
> @@ -706,6 +726,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> goto keep;
>
> VM_BUG_ON(PageActive(page));
> + VM_BUG_ON(page_zone(page) != zone);
?
> sc->nr_scanned++;
>
>
> ...
>
> @@ -903,6 +928,15 @@ keep_lumpy:
> VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
> }
>
> + /*
> + * Tag a zone as congested if all the dirty pages encountered were
> + * backed by a congested BDI. In this case, reclaimers should just
> + * back off and wait for congestion to clear because further reclaim
> + * will encounter the same problem
> + */
> + if (nr_dirty == nr_congested)
> + zone_set_flag(zone, ZONE_CONGESTED);
The implicit "100%" there is a magic number. hrm.
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next prev parent reply other threads:[~2010-09-16 22:28 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-15 12:27 [PATCH 0/8] Reduce latencies and improve overall reclaim efficiency v2 Mel Gorman
2010-09-15 12:27 ` [PATCH 1/8] tracing, vmscan: Add trace events for LRU list shrinking Mel Gorman
2010-09-15 12:27 ` [PATCH 2/8] writeback: Account for time spent congestion_waited Mel Gorman
2010-09-15 12:27 ` [PATCH 3/8] vmscan: Synchronous lumpy reclaim should not call congestion_wait() Mel Gorman
2010-09-15 12:27 ` [PATCH 4/8] vmscan: Narrow the scenarios lumpy reclaim uses synchrounous reclaim Mel Gorman
2010-09-15 12:27 ` [PATCH 5/8] vmscan: Remove dead code in shrink_inactive_list() Mel Gorman
2010-09-15 12:27 ` [PATCH 6/8] vmscan: isolated_lru_pages() stop neighbour search if neighbour cannot be isolated Mel Gorman
2010-09-15 12:27 ` [PATCH 7/8] writeback: Do not sleep on the congestion queue if there are no congested BDIs Mel Gorman
2010-09-16 7:59 ` Minchan Kim
2010-09-16 8:23 ` Mel Gorman
2010-09-15 12:27 ` [PATCH 8/8] writeback: Do not sleep on the congestion queue if there are no congested BDIs or if significant congestion is not being encountered in the current zone Mel Gorman
2010-09-16 8:13 ` Minchan Kim
2010-09-16 9:18 ` Mel Gorman
2010-09-16 14:11 ` Minchan Kim
2010-09-16 15:18 ` Mel Gorman
2010-09-16 22:28 ` Andrew Morton [this message]
2010-09-20 9:52 ` Mel Gorman
2010-09-21 21:44 ` Andrew Morton
2010-09-21 22:10 ` Mel Gorman
2010-09-21 22:24 ` Andrew Morton
2010-09-20 13:05 ` [PATCH] writeback: Do not sleep on the congestion queue if there are no congested BDIs or if significant congestion is not being encounted in the current zone fix Mel Gorman
2010-09-16 22:28 ` [PATCH 0/8] Reduce latencies and improve overall reclaim efficiency v2 Andrew Morton
2010-09-17 7:52 ` Mel Gorman
2010-10-14 15:28 ` Christian Ehrhardt
2010-10-18 13:55 ` Mel Gorman
2010-10-22 12:29 ` Christian Ehrhardt
2010-11-03 10:50 ` Christian Ehrhardt
2010-11-10 14:37 ` Mel Gorman
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