linux-kernel - Re: [v2 PATCH] mm: vmscan: correct nr

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Message-ID: <3c2ef3c2-4d39-11c3-acfa-2a809ca72b3c@linux.alibaba.com>
Date:   Tue, 21 May 2019 14:54:10 +0800
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Michal Hocko <mhocko@...nel.org>, Yang Shi <shy828301@...il.com>,
        Huang Ying <ying.huang@...el.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        kirill.shutemov@...ux.intel.com, Hugh Dickins <hughd@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        william.kucharski@...cle.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [v2 PATCH] mm: vmscan: correct nr_reclaimed for THP


> [ check_move_unevictable_pages() seems weird. It gets a pagevec from
>    find_get_entries(), which, if I understand the THP page cache code
>    correctly, might contain the same compound page over and over. It'll
>    be !unevictable after the first iteration, so will only run once. So
>    it produces incorrect numbers now, but it is probably best to ignore
>    it until we figure out THP cache. Maybe add an XXX comment. ]

The commit 5fd4ca2d84b2 ("mm: page cache: store only head pages in 
i_pages") changed how THP is stored in page cache, but 
find_get_entries() would return base page by calling find_subpage(), so 
check_move_unevictable_pages() should just returns the number of base pages.