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From: "Huang\, Ying" <ying.huang@intel.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: David Hildenbrand <david@redhat.com>,
	 Matthew Wilcox <willy@infradead.org>,
	 Andrew Morton <akpm@linux-foundation.org>,  <linux-mm@kvack.org>,
	 <linux-kernel@vger.kernel.org>,  Mel Gorman <mgorman@suse.de>,
	 Vlastimil Babka <vbabka@suse.cz>,  Zi Yan <ziy@nvidia.com>,
	 Peter Zijlstra <peterz@infradead.org>,
	 Dave Hansen <dave.hansen@linux.intel.com>,
	 Minchan Kim <minchan@kernel.org>,
	 "Johannes Weiner" <hannes@cmpxchg.org>,
	 Hugh Dickins <hughd@google.com>,
	 "Alexander Duyck" <alexander.duyck@gmail.com>
Subject: Re: [RFC 0/3] mm: Discard lazily freed pages when migrating
Date: Tue, 03 Mar 2020 19:36:57 +0800	[thread overview]
Message-ID: <87k1414qli.fsf@yhuang-dev.intel.com> (raw)
In-Reply-To: <20200303081929.GY4380@dhcp22.suse.cz> (Michal Hocko's message of "Tue, 3 Mar 2020 09:19:29 +0100")

Michal Hocko <mhocko@kernel.org> writes:

> On Tue 03-03-20 09:30:28, Huang, Ying wrote:
> [...]
>> Yes.  mmap() can control whether to populate the underlying physical
>> pages.
>
> right because many usecases benefit from it. They simply know that the
> mapping will be used completely and it is worth saving overhead for #PF.
> See. there is a clear justification for that policy.
>
>> But for migrating MADV_FREE pages, there's no control, all pages
>> will be populated again always by default.  Maybe we should avoid to do
>> that in some situations too.
>
> Now let's have a look here. It is the userspace that decided to mark
> MADV_FREE pages. It is under its full control which pages are to be
> freed lazily. If the userspace wants to move those pages then it is
> likely aware they have been MADV_FREE, right? If the userspace wanted to
> save migration overhead then it could either chose to not migrate those
> pages or simply unmap them right away. So in the end we are talking
> about saving munmap/MAMDV_DONTNEED or potentially more move_pages calls
> to skip over MADV_FREE holes. Which is all nice but is there any
> userspace that really does care? Because this is a fundamental question
> here and it doesn't make much sense to discuss this left to right unless
> this is clear.

Although I don't agree with you, I don't want to continue.  Because I
feel that the discussion may be too general to go anywhere.  I admit
that I go to the general side firstly, sorry about that.

Best Regards,
Huang, Ying


      reply	other threads:[~2020-03-03 11:37 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-28  3:38 [RFC 0/3] mm: Discard lazily freed pages when migrating Huang, Ying
2020-02-28  3:38 ` [RFC 1/3] mm, migrate: Check return value of try_to_unmap() Huang, Ying
2020-02-28  3:38 ` [RFC 2/3] mm: Add a new page flag PageLayzyFree() for MADV_FREE Huang, Ying
2020-02-28  6:13   ` David Hildenbrand
2020-02-28  6:47     ` Huang, Ying
2020-03-15  8:18   ` Wei Yang
2020-03-15  8:54     ` Mika Penttilä
2020-03-15 12:22       ` Wei Yang
2020-03-16  1:21         ` Huang, Ying
2020-03-16 22:38           ` Wei Yang
2020-02-28  3:38 ` [RFC 3/3] mm: Discard lazily freed pages when migrating Huang, Ying
2020-02-28  3:42 ` [RFC 0/3] " Matthew Wilcox
2020-02-28  7:25   ` Huang, Ying
2020-02-28  8:22     ` David Hildenbrand
2020-02-28  8:55       ` Huang, Ying
2020-02-28  9:49         ` Mel Gorman
2020-03-02 11:23           ` Huang, Ying
2020-03-02 15:16             ` Mel Gorman
2020-03-03  1:51               ` Huang, Ying
2020-03-03  8:09                 ` Michal Hocko
2020-03-03  8:47                   ` Huang, Ying
2020-03-03  8:58                     ` Michal Hocko
2020-03-03 11:49                       ` Huang, Ying
2020-03-04  9:58                         ` Michal Hocko
2020-03-04 10:56                           ` Mel Gorman
2020-03-05  1:42                             ` Huang, Ying
2020-03-04 11:15                           ` Huang, Ying
2020-03-04 11:26                             ` Michal Hocko
2020-03-05  1:45                               ` Huang, Ying
2020-03-05 10:48                             ` Mel Gorman
2020-03-06  4:05                               ` Huang, Ying
2020-03-09  5:26                               ` Huang, Ying
2020-03-03 13:02                 ` Mel Gorman
2020-03-04  0:33                   ` Huang, Ying
2020-02-28  9:50         ` Michal Hocko
2020-02-28 10:15           ` Michal Hocko
2020-02-28 13:45           ` Johannes Weiner
2020-03-02 14:12           ` Huang, Ying
2020-03-02 14:23             ` David Hildenbrand
2020-03-03  0:25               ` Huang, Ying
2020-03-02 14:25             ` Michal Hocko
2020-03-03  1:30               ` Huang, Ying
2020-03-03  8:19                 ` Michal Hocko
2020-03-03 11:36                   ` Huang, Ying [this message]

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