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From: Rik van Riel <riel@surriel.com>
To: David Hildenbrand <david@redhat.com>,
	alexlzhu@fb.com, linux-mm@kvack.org
Cc: willy@infradead.org, hannes@cmpxchg.org,
	akpm@linux-foundation.org, kernel-team@fb.com,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC 2/3] mm: changes to split_huge_page() to free zero filled tail pages
Date: Mon, 29 Aug 2022 09:17:07 -0400	[thread overview]
Message-ID: <37db29410990991555362154a371b58f47d3cb0c.camel@surriel.com> (raw)
In-Reply-To: <42c164c6-8c69-7b4b-d965-ac62d1607061@redhat.com>

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On Mon, 2022-08-29 at 12:02 +0200, David Hildenbrand wrote:
> On 26.08.22 23:18, Rik van Riel wrote:
> > On Fri, 2022-08-26 at 12:18 +0200, David Hildenbrand wrote:
> > > On 25.08.22 23:30, alexlzhu@fb.com wrote:
> > > > From: Alexander Zhu <alexlzhu@fb.com>
> > 
> > I could see wanting to maybe consolidate the scanning between
> > KSM and this thing at some point, if it could be done without
> > too much complexity, but keeping this change to split_huge_page
> > looks like it might make sense even when KSM is enabled, since
> > it will get rid of the unnecessary memory much faster than KSM
> > could.
> > 
> > Keeping a hundred MB of unnecessary memory around for longer
> > would simply result in more THPs getting split up, and more
> > memory pressure for a longer time than we need.
> 
> Right. I was wondering if we want to map the shared zeropage instead
> of
> the "detected to be zero" page, similar to how KSM would do it. For
> example, with userfaultfd there would be an observable difference.
> 
> (maybe that's already done in this patch set)
> 
The patch does not currently do that, but I suppose it could?

What exactly are the userfaultfd differences here, and how does
dropping 4kB pages break things vs. using the shared zeropage?

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  reply	other threads:[~2022-08-29 13:21 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-25 21:30 [RFC 0/3] THP Shrinker alexlzhu
2022-08-25 21:30 ` [RFC 1/3] mm: add thp_utilization metrics to debugfs alexlzhu
2022-08-27  0:11   ` Zi Yan
2022-08-29 20:19     ` Alex Zhu (Kernel)
2022-08-25 21:30 ` [RFC 2/3] mm: changes to split_huge_page() to free zero filled tail pages alexlzhu
2022-08-26 10:18   ` David Hildenbrand
2022-08-26 18:34     ` Alex Zhu (Kernel)
2022-08-26 21:18     ` Rik van Riel
2022-08-29 10:02       ` David Hildenbrand
2022-08-29 13:17         ` Rik van Riel [this message]
2022-08-30 12:33           ` David Hildenbrand
2022-08-30 21:54             ` Alex Zhu (Kernel)
2022-08-25 21:30 ` [RFC 3/3] mm: THP low utilization shrinker alexlzhu
2022-08-27  0:25   ` Zi Yan
2022-08-29 20:49     ` Alex Zhu (Kernel)

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