From: Andrew Morton <akpm@linux-foundation.org>
To: Hugh Dickins <hughd@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
Konstantin Khlebnikov <khlebnikov@openvz.org>,
linux-mm@kvack.org, Mel Gorman <mel@csn.ul.ie>
Subject: Re: [PATCH 3/3] mm: take pagevecs off reclaim stack
Date: Thu, 29 Dec 2011 19:59:17 -0800 [thread overview]
Message-ID: <20111229195917.13f15974.akpm@linux-foundation.org> (raw)
In-Reply-To: <alpine.LSU.2.00.1112291753350.3614@eggly.anvils>
On Thu, 29 Dec 2011 17:55:14 -0800 (PST) Hugh Dickins <hughd@google.com> wrote:
> > However, at that time, I think this patch behave
> > better than old. If we release and retake zone lock per 14 pages,
> > other tasks can easily steal a part of lumpy reclaimed pages. and then
> > long latency wrongness will be happen when system is under large page
> > memory allocation pressure. That's the reason why I posted very similar patch
> > a long time ago.
>
> Aha, and another good point. Thank you.
I hope you understand it better than I :(
Long lock hold times and long irq-off times are demonstrable problems
which have hurt people in the past. Whereas the someone-stole-my-page
issue is theoretical, undemonstrated and unquantified. And for
some people, lengthy worst-case latency is a serious problem, doesn't
matter whether the system is under memory pressure or not - that simply
determines when the worst-case hits.
This is not all some handwavy theoretical thing either. If we've gone
and introduced serious latency issues, people *will* hit them and treat
it as a regression.
Now, a way out here is to remove lumpy reclaim (please). And make the
problem not come back by promising to never call putback_lru_pages(lots
of pages) (how do we do this?).
So I think the best way ahead here is to distribute this patch in the
same release in which we remove lumpy reclaim (pokes Mel).
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next prev parent reply other threads:[~2011-12-30 3:55 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-29 4:32 [PATCH 0/3] mm: three minor vmscan improvements Hugh Dickins
2011-12-29 4:35 ` [PATCH 1/3] mm: test PageSwapBacked in lumpy reclaim Hugh Dickins
2011-12-29 5:06 ` KOSAKI Motohiro
2012-01-04 1:23 ` Minchan Kim
2012-01-05 6:03 ` KAMEZAWA Hiroyuki
2011-12-29 4:36 ` [PATCH 2/3] mm: cond_resched in scan_mapping_unevictable_pages Hugh Dickins
2011-12-29 5:14 ` KOSAKI Motohiro
2011-12-29 5:48 ` Hugh Dickins
2011-12-29 22:46 ` Hugh Dickins
2011-12-29 4:39 ` [PATCH 3/3] mm: take pagevecs off reclaim stack Hugh Dickins
2011-12-29 5:42 ` KOSAKI Motohiro
2011-12-29 11:18 ` Konstantin Khlebnikov
2011-12-29 22:20 ` Hugh Dickins
2011-12-29 22:55 ` Andrew Morton
2011-12-29 23:27 ` Hugh Dickins
2011-12-30 0:24 ` KOSAKI Motohiro
2011-12-30 1:55 ` Hugh Dickins
2011-12-30 3:59 ` Andrew Morton [this message]
2011-12-30 15:51 ` Mel Gorman
2012-01-01 7:18 ` Hugh Dickins
2012-01-03 23:12 ` Andrew Morton
2012-01-03 23:17 ` KOSAKI Motohiro
2012-01-03 23:29 ` Andrew Morton
2012-01-04 0:03 ` KOSAKI Motohiro
2012-01-04 3:22 ` Hugh Dickins
2012-01-04 20:20 ` Andrew Morton
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