From: Vlastimil Babka <vbabka@suse.cz>
To: David Hildenbrand <david@redhat.com>,
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 09:55:29 +0200 [thread overview]
Message-ID: <09885eda-9772-4228-dece-3dfd42840580@suse.cz> (raw)
In-Reply-To: <d15623f5-5c89-b9e5-1787-61ad70519774@redhat.com>
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.
next prev parent reply other threads:[~2020-04-24 7:55 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 [this message]
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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