From: Mel Gorman <mgorman@techsingularity.net>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Lucas Stach <l.stach@pengutronix.de>,
Michal Hocko <mhocko@suse.com>, Vlastimil Babka <vbabka@suse.cz>,
linux-mm@kvack.org, kernel@pengutronix.de,
patchwork-lst@pengutronix.de
Subject: Re: [PATCH] mm: page_alloc: avoid excessive IRQ disabled times in free_unref_page_list
Date: Fri, 8 Dec 2017 10:21:30 +0000 [thread overview]
Message-ID: <20171208102130.4d4rwpwkseziniug@techsingularity.net> (raw)
In-Reply-To: <20171207165317.9ef234b9f83cb62cdad72427@linux-foundation.org>
On Thu, Dec 07, 2017 at 04:53:17PM -0800, Andrew Morton wrote:
> On Fri, 8 Dec 2017 00:25:37 +0000 Mel Gorman <mgorman@techsingularity.net> wrote:
>
> > Well, it's release_pages. From core VM and the block layer, not very long
> > but for drivers and filesystems, it can be arbitrarily long. Even from the
> > VM, the function can be called a lot but as it's from pagevec context so
> > it's naturally broken into small pieces anyway.
>
> OK.
>
> > > If "significantly" then there may be additional benefit in rearranging
> > > free_hot_cold_page_list() so it only walks a small number of list
> > > entries at a time. So the data from the first loop is still in cache
> > > during execution of the second loop. And that way this
> > > long-irq-off-time problem gets fixed automagically.
> > >
> >
> > I'm not sure it's worthwhile. In too many cases, the list of pages being
> > released are either cache cold or are so long that the cache data is
> > being thrashed anyway.
>
> Well, whether the incoming data is cache-cold or very-long, doing that
> double pass in small bites would reduce thrashing.
>
> > Once the core page allocator is involved, then
> > there will be further cache thrashing due to buddy page merging accessing
> > data that is potentially very close. I think it's unlikely there would be
> > much value in using alternative schemes unless we were willing to have
> > very large per-cpu lists -- something I prototyped for fast networking
> > but never heard back whether it's worthwhile or not.
>
> I mean something like this....
>
Ok yes, I see. That is a viable alternative to Lucas's patch that should
achieve the same result with the bonus of some of the entries still being
cache hot. Lucas, care to give it a spin and see does it also address
your problem?
--
Mel Gorman
SUSE Labs
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next prev parent reply other threads:[~2017-12-08 10:21 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-07 17:03 [PATCH] mm: page_alloc: avoid excessive IRQ disabled times in free_unref_page_list Lucas Stach
2017-12-07 19:51 ` Mel Gorman
2017-12-07 23:20 ` Andrew Morton
2017-12-08 0:25 ` Mel Gorman
2017-12-08 0:53 ` Andrew Morton
2017-12-08 10:21 ` Mel Gorman [this message]
2017-12-08 10:03 ` Lucas Stach
2017-12-08 11:38 ` Mel Gorman
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