From: Vlastimil Babka <vbabka@suse.cz>
To: Andrew Morton <akpm@linux-foundation.org>,
Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>,
Mel Gorman <mgorman@techsingularity.net>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Andrea Arcangeli <aarcange@redhat.com>,
Dan Williams <dan.j.williams@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
David Hildenbrand <david@redhat.com>,
Michal Hocko <mhocko@kernel.org>,
Alex Williamson <alex.williamson@redhat.com>
Subject: Re: [RFC PATCH 4/4] mm: Add PG_zero support
Date: Wed, 22 Apr 2020 16:09:00 +0200 [thread overview]
Message-ID: <344a3a78-62ad-48fe-40cf-18993175d1e0@suse.cz> (raw)
In-Reply-To: <20200413140537.eb674579cf8c71b4e20581ab@linux-foundation.org>
On 4/13/20 11:05 PM, Andrew Morton wrote:
> On Mon, 13 Apr 2020 08:11:59 -0700 Alexander Duyck <alexander.h.duyck@linux.intel.com> wrote:
>
>> In addition, unlike madvising the page away there is a pretty
>> significant performance penalty for having to clear the page a second
>> time when the page is split or merged.
>
> I wonder if there might be an issue with increased memory traffic (and
> increased energy consumption, etc). If a page is zeroed immediately
> before getting data written into it (eg, plain old file write(),
> anonymous pagefault) then we can expect that those 4096 zeroes will be
> in CPU cache and mostly not written back. But if that page was zeroed
> a "long" time ago, the caches will probably have been written back.
> Net result: we go from 4k of memory traffic for a 4k page up to 8k of
> memory traffic?
Heh, I was quite sure that this is not the first time background zeroing is
proposed, so I went to google for it... and found that one BSD kernel actually
removed this functionality in 2016 [1] and this was one of the reasons.
[1]
https://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/afd2da4dc9056ea79cdf15e8a9386a3d3998f33e
> Also, the name CONFIG_ZERO_PAGE sounds like it has something to do with
> the long established "zero page". Confusing. CONFIG_PREZERO_PAGE,
> maybe?
>
next prev parent reply other threads:[~2020-04-22 14:09 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-12 9:09 [RFC PATCH 4/4] mm: Add PG_zero support liliangleo
2020-04-12 10:12 ` Matthew Wilcox
2020-04-13 15:11 ` Alexander Duyck
2020-04-13 21:05 ` Andrew Morton
2020-04-22 14:09 ` Vlastimil Babka [this message]
2020-04-24 0:37 ` Andrew Morton
2020-04-24 0:41 ` Matthew Wilcox
2020-04-24 7:28 ` David Hildenbrand
2020-04-24 7:55 ` Vlastimil Babka
2020-04-24 7:57 ` David Hildenbrand
2020-04-15 5:15 ` [mm] 5ae8a9d7c8: will-it-scale.per_thread_ops -2.1% regression kernel test robot
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