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From: "Huang\, Ying" <ying.huang@intel.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>,
	 David Hildenbrand <david@redhat.com>,
	 Johannes Weiner <hannes@cmpxchg.org>,
	 Matthew Wilcox <willy@infradead.org>,
	 Andrew Morton <akpm@linux-foundation.org>,  <linux-mm@kvack.org>,
	 <linux-kernel@vger.kernel.org>,
	 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>,
	 Hugh Dickins <hughd@google.com>,
	 Alexander Duyck <alexander.duyck@gmail.com>
Subject: Re: [RFC 0/3] mm: Discard lazily freed pages when migrating
Date: Thu, 05 Mar 2020 09:45:11 +0800	[thread overview]
Message-ID: <8736an3788.fsf@yhuang-dev.intel.com> (raw)
In-Reply-To: <20200304112653.GH16139@dhcp22.suse.cz> (Michal Hocko's message of "Wed, 4 Mar 2020 12:26:53 +0100")

Michal Hocko <mhocko@kernel.org> writes:

> On Wed 04-03-20 19:15:20, Huang, Ying wrote:
>> Michal Hocko <mhocko@kernel.org> writes:
>> 
>> > On Tue 03-03-20 19:49:53, Huang, Ying wrote:
> [...]
>> >> Because the penalty difference is so large, I
>> >> think it may be a good idea to always put clean MADV_FREE pages at the
>> >> tail of the inactive file LRU list?
>> >
>> > You are again making assumptions without giving any actual real
>> > examples. Reconstructing MADV_FREE pages cost can differ a lot.
>> 
>> In which situation the cost to reconstruct MADV_FREE pages can be higher
>> than the cost to allocate file cache page and read from disk?  Heavy
>> contention on mmap_sem?
>
> Allocating a page might be really costly but even without that.

File cache page needs to be allocated too.

> Reconstructnig the content of the page can be really high and actually
> much larger than an IO to get a page from the storage. Consider
> decompression or some other transformations to get the content.
> Userspace has means to detect that the content is still up-to-date as
> already has been mentioned so all those steps can be avoided.

Although I don't believe someone has really done this.  It's possible at
least in theory.

Best Regards,
Huang, Ying


  reply	other threads:[~2020-03-05  1:45 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 [this message]
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

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