From: David Hildenbrand <david@redhat.com>
To: Vlastimil Babka <vbabka@suse.cz>,
Matthew Wilcox <willy@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>,
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>,
Michal Hocko <mhocko@kernel.org>,
Alex Williamson <alex.williamson@redhat.com>
Subject: Re: [RFC PATCH 4/4] mm: Add PG_zero support
Date: Fri, 24 Apr 2020 09:57:50 +0200 [thread overview]
Message-ID: <0d73b277-1b4d-1613-8b42-29826563f51a@redhat.com> (raw)
In-Reply-To: <09885eda-9772-4228-dece-3dfd42840580@suse.cz>
On 24.04.20 09:55, Vlastimil Babka wrote:
> On 4/24/20 9:28 AM, David Hildenbrand wrote:
>> On 24.04.20 02:41, Matthew Wilcox wrote:
>>> On Thu, Apr 23, 2020 at 05:37:00PM -0700, Andrew Morton wrote:
>>>> On Wed, 22 Apr 2020 16:09:00 +0200 Vlastimil Babka <vbabka@suse.cz> wrote:
>>>>> 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
>>>>
>>>> Interesting.
>>>>
>>>> However this:
>>>>
>>>> - Pre-zeroing a page leads to a cold-cache case on-use, forcing the fault
>>>> source (e.g. a userland program) to actually get the data from main
>>>> memory in its likely immediate use of the faulted page, reducing
>>>> performance.
>>>>
>>>> implies that BSD was zeroing with non-temporal stores which bypass the
>>>> CPU cache. And which presumably invalidate any part of the target
>>>> memory which was already in cache. We wouldn't do it that way so
>>>> perhaps the results would differ.
>>>
>>> Or just that the page was zeroed far enough in advance that it fell out
>>> of cache naturally.
>
> Agreed.
>
>>> I know Arjan looked at zeroing on free instead of zeroing on alloc,
>>> and that didn't get merged (or even submitted afaik), so presumably the
>>> results weren't good.
>>
>> We do have INIT_ON_FREE_DEFAULT_ON
>>
>> via
>>
>> commit 6471384af2a6530696fc0203bafe4de41a23c9ef
>> Author: Alexander Potapenko <glider@google.com>
>> Date: Thu Jul 11 20:59:19 2019 -0700
>>
>> mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options
>>
>> which seems to do exactly that (although for a different use case)
>
> Yeah, except the security use case wants to do that immediately, while the
> proposal here is a background thread.
>
Yes I know, this was just a comment regarding "Arjan looked at zeroing
on free instead of zeroing on alloc".
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2020-04-24 7:58 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
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 [this message]
2020-04-15 5:15 ` [mm] 5ae8a9d7c8: will-it-scale.per_thread_ops -2.1% regression kernel test robot
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