linux-kernel - RE: [PATCH -v3 00/10] THP swap: Delay splitting THP during swapping out

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Date:   Thu, 22 Sep 2016 23:49:00 +0000
From:   "Chen, Tim C" <tim.c.chen@...el.com>
To:     Shaohua Li <shli@...nel.org>, "Huang, Ying" <ying.huang@...el.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Kleen, Andi" <andi.kleen@...el.com>,
        "Lu, Aaron" <aaron.lu@...el.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Rik van Riel <riel@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vladimir Davydov <vdavydov@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>
Subject: RE: [PATCH -v3 00/10] THP swap: Delay splitting THP during swapping
 out

>
>So this is impossible without THP swapin. While 2M swapout makes a lot of
>sense, I doubt 2M swapin is really useful. What kind of application is 'optimized'
>to do sequential memory access?

We waste a lot of cpu cycles to re-compact 4K pages back to a large page
under THP.  Swapping it back in as a single large page can avoid
fragmentation and this overhead.

Thanks.

Tim