linux-kernel - Re: [PATCH] mm, compaction: fix NR_ISOLATED

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Date:   Thu, 20 Oct 2016 20:16:06 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     "ming.ling" <ming.ling@...eadtrum.com>,
        Minchan Kim <minchan@...nel.org>, Mel Gorman <mgorman@...e.de>,
        Vlastimil Babka <vbabka@...e.cz>,
        Joonsoo Kim <js1304@...il.com>, <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH] mm, compaction: fix NR_ISOLATED_* stats for pfn based
 migration

On Wed, 19 Oct 2016 10:02:40 +0200 Michal Hocko <mhocko@...nel.org> wrote:

> Since bda807d44454 ("mm: migrate: support non-lru movable page
> migration") isolate_migratepages_block) can isolate !PageLRU pages which
> would acct_isolated account as NR_ISOLATED_*. Accounting these non-lru
> pages NR_ISOLATED_{ANON,FILE} doesn't make any sense and it can misguide
> heuristics based on those counters such as pgdat_reclaimable_pages resp.
> too_many_isolated which would lead to unexpected stalls during the
> direct reclaim without any good reason. Note that
> __alloc_contig_migrate_range can isolate a lot of pages at once.
> 
> On mobile devices such as 512M ram android Phone, it may use a big zram
> swap. In some cases zram(zsmalloc) uses too many non-lru but migratedable
> pages, such as:
> 
>       MemTotal: 468148 kB
>       Normal free:5620kB
>       Free swap:4736kB
>       Total swap:409596kB
>       ZRAM: 164616kB(zsmalloc non-lru pages)
>       active_anon:60700kB
>       inactive_anon:60744kB
>       active_file:34420kB
>       inactive_file:37532kB
> 
> Fix this by only accounting lru pages to NR_ISOLATED_* in
> isolate_migratepages_block right after they were isolated and we still
> know they were on LRU. Drop acct_isolated because it is called after the
> fact and we've lost that information. Batching per-cpu counter doesn't
> make much improvement anyway. Also make sure that we uncharge only LRU
> pages when putting them back on the LRU in putback_movable_pages resp.
> when unmap_and_move migrates the page.

It isn't worth backporting into 4.8.x?