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From: Dave Hansen <dave.hansen@intel.com>
To: Greg Thelen <gthelen@google.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, kbusch@kernel.org,
	yang.shi@linux.alibaba.com, rientjes@google.com,
	ying.huang@intel.com, dan.j.williams@intel.com
Subject: Re: [RFC][PATCH 2/8] mm/migrate: Defer allocating new page until needed
Date: Wed, 1 Jul 2020 07:46:34 -0700
Message-ID: <977d6482-58f8-c1c8-c54d-7c03a028c532@intel.com> (raw)
In-Reply-To: <xr93lfk38vw0.fsf@gthelen.svl.corp.google.com>

On 7/1/20 1:47 AM, Greg Thelen wrote:
> Dave Hansen <dave.hansen@linux.intel.com> wrote:
>> From: Keith Busch <kbusch@kernel.org>
>> Defer allocating the page until we are actually ready to make use of
>> it, after locking the original page. This simplifies error handling,
>> but should not have any functional change in behavior. This is just
>> refactoring page migration so the main part can more easily be reused
>> by other code.
> 
> Is there any concern that the src page is now held PG_locked over the
> dst page allocation, which might wander into
> reclaim/cond_resched/oom_kill?  I don't have a deadlock in mind.  I'm
> just wondering about the additional latency imposed on unrelated threads
> who want access src page.

It's not great.  *But*, the alternative is to toss the page contents out
and let users encounter a fault and an allocation.  They would be
subject to all the latency associated with an allocation, just at a
slightly later time.

If it's a problem it seems like it would be pretty easy to fix, at least
for non-cgroup reclaim.  We know which node we're reclaiming from and we
know if it has a demotion path, so we could proactively allocate a
single migration target page before doing the source lock_page().  That
creates some other problems, but I think it would be straightforward.

>> #Signed-off-by: Keith Busch <keith.busch@intel.com>
> 
> Is commented Signed-off-by intentional?  Same applies to later patches.

Yes, Keith is no longer at Intel, so that @intel.com mail would bounce.
 I left the @intel.com SoB so it would be clear that the code originated
from Keith while at Intel, but commented it out to avoid it being picked
up by anyone's tooling.


  reply index

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-29 23:45 [RFC][PATCH 0/8] Migrate Pages in lieu of discard Dave Hansen
2020-06-29 23:45 ` [RFC][PATCH 1/8] mm/numa: node demotion data structure and lookup Dave Hansen
2020-06-29 23:45 ` [RFC][PATCH 2/8] mm/migrate: Defer allocating new page until needed Dave Hansen
2020-07-01  8:47   ` Greg Thelen
2020-07-01 14:46     ` Dave Hansen [this message]
2020-07-01 18:32       ` Yang Shi
2020-06-29 23:45 ` [RFC][PATCH 3/8] mm/vmscan: Attempt to migrate page in lieu of discard Dave Hansen
2020-07-01  0:47   ` David Rientjes
2020-07-01  1:29     ` Yang Shi
2020-07-01  5:41       ` David Rientjes
2020-07-01  8:54         ` Huang, Ying
2020-07-01 18:20           ` Dave Hansen
2020-07-01 19:50             ` David Rientjes
2020-07-02  1:50               ` Huang, Ying
2020-07-01 15:15         ` Dave Hansen
2020-07-01 17:21         ` Yang Shi
2020-07-01 19:45           ` David Rientjes
2020-07-02 10:02             ` Jonathan Cameron
2020-07-01  1:40     ` Huang, Ying
2020-07-01 16:48     ` Dave Hansen
2020-07-01 19:25       ` David Rientjes
2020-07-02  5:02         ` Huang, Ying
2020-06-29 23:45 ` [RFC][PATCH 4/8] mm/vmscan: add page demotion counter Dave Hansen
2020-06-29 23:45 ` [RFC][PATCH 5/8] mm/numa: automatically generate node migration order Dave Hansen
2020-06-30  8:22   ` Huang, Ying
2020-07-01 18:23     ` Dave Hansen
2020-07-02  1:20       ` Huang, Ying
2020-06-29 23:45 ` [RFC][PATCH 6/8] mm/vmscan: Consider anonymous pages without swap Dave Hansen
2020-06-29 23:45 ` [RFC][PATCH 7/8] mm/vmscan: never demote for memcg reclaim Dave Hansen
2020-06-29 23:45 ` [RFC][PATCH 8/8] mm/numa: new reclaim mode to enable reclaim-based migration Dave Hansen
2020-06-30  7:23   ` Huang, Ying
2020-06-30 17:50     ` Yang Shi
2020-07-01  0:48       ` Huang, Ying
2020-07-01  1:12         ` Yang Shi
2020-07-01  1:28           ` Huang, Ying
2020-07-01 16:02       ` Dave Hansen
2020-07-03  9:30   ` Huang, Ying
2020-06-30 18:36 ` [RFC][PATCH 0/8] Migrate Pages in lieu of discard Shakeel Butt
2020-06-30 18:51   ` Dave Hansen
2020-06-30 19:25     ` Shakeel Butt
2020-06-30 19:31       ` Dave Hansen
2020-07-01 14:24         ` [RFC] [PATCH " Zi Yan
2020-07-01 14:32           ` Dave Hansen

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