[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <8736an3788.fsf@yhuang-dev.intel.com>
Date: Thu, 05 Mar 2020 09:45:11 +0800
From: "Huang\, Ying" <ying.huang@...el.com>
To: Michal Hocko <mhocko@...nel.org>
Cc: Mel Gorman <mgorman@...e.de>, David Hildenbrand <david@...hat.com>,
Johannes Weiner <hannes@...xchg.org>,
Matthew Wilcox <willy@...radead.org>,
Andrew Morton <akpm@...ux-foundation.org>,
<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
Vlastimil Babka <vbabka@...e.cz>, Zi Yan <ziy@...dia.com>,
Peter Zijlstra <peterz@...radead.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Minchan Kim <minchan@...nel.org>,
Hugh Dickins <hughd@...gle.com>,
Alexander Duyck <alexander.duyck@...il.com>
Subject: Re: [RFC 0/3] mm: Discard lazily freed pages when migrating
Michal Hocko <mhocko@...nel.org> writes:
> On Wed 04-03-20 19:15:20, Huang, Ying wrote:
>> Michal Hocko <mhocko@...nel.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
Powered by blists - more mailing lists