From: Hugh Dickins <hughd@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>, linux-mm@kvack.org
Subject: Re: [PATCH 3/3] mm: take pagevecs off reclaim stack
Date: Thu, 29 Dec 2011 15:27:17 -0800 (PST) [thread overview]
Message-ID: <alpine.LSU.2.00.1112291510390.4888@eggly.anvils> (raw)
In-Reply-To: <20111229145548.e34cb2f3.akpm@linux-foundation.org>
On Thu, 29 Dec 2011, Andrew Morton wrote:
> On Wed, 28 Dec 2011 20:39:36 -0800 (PST)
> Hugh Dickins <hughd@google.com> wrote:
>
> > Replace pagevecs in putback_lru_pages() and move_active_pages_to_lru()
> > by lists of pages_to_free
>
> One effect of the pagevec handling was to limit lru_lock hold times and
> interrupt-disabled times.
>
> This patch removes that upper bound and has the potential to cause
> various latency problems when processing large numbers of pages.
>
> The affected functions have rather a lot of callers. I don't think
> that auditing all these callers and convincing ourselves that none of
> them pass in 10,000 pages is sufficient, because that doesn't prevent us
> from introducing such latency problems as the MM code evolves.
That's an interesting slant on it, that hadn't crossed my mind;
but it looks like intervening changes have answered that concern.
putback_lru_pages() has one caller, shrink_inactive_list();
move_active_pages_to_lru() has one caller, shrink_active_list().
Following those back, they're in all cases capped to SWAP_CLUSTER_MAX
pages per call. That's 32 pages, not so very much more than the 14
page limit the pagevecs were imposing.
And both shrink_inactive_list() and shrink_active_list() gather these
pages with isolate_lru_pages(), which does not drop lock or enable
interrupts at all - probably why the SWAP_CLUSTER_MAX cap got imposed.
(Don't be deceived by mm/migrate.c's putback_lru_pages()!
That's a distinct function, unaffected by this patch.)
Hugh
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next prev parent reply other threads:[~2011-12-29 23:27 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 [this message]
2011-12-30 0:24 ` KOSAKI Motohiro
2011-12-30 1:55 ` Hugh Dickins
2011-12-30 3:59 ` Andrew Morton
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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