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Date:   Fri, 13 Mar 2020 16:41:10 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     "Huang, Ying" <ying.huang@intel.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, David Hildenbrand <david@redhat.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        David Rientjes <rientjes@google.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Mel Gorman <mgorman@suse.de>, Vlastimil Babka <vbabka@suse.cz>,
        Minchan Kim <minchan@kernel.org>,
        Hugh Dickins <hughd@google.com>,
        Rik van Riel <riel@surriel.com>
Subject: Re: [PATCH] mm: Code cleanup for MADV_FREE
Message-ID: <20200313154110.GH21007@dhcp22.suse.cz>
References: <20200313090056.2104105-1-ying.huang@intel.com>
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On Fri 13-03-20 17:00:56, Huang, Ying wrote:
> From: Huang Ying <ying.huang@intel.com>
> 
> Some comments for MADV_FREE is revised and added to help people understand the
> MADV_FREE code, especially the page flag, PG_swapbacked.  This makes
> page_is_file_cache() isn't consistent with its comments.  So the function is
> renamed to page_is_file_lru() to make them consistent again.  All these are put
> in one patch as one logical change.
> 
> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
> Suggested-by: David Rientjes <rientjes@google.com>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Rik van Riel <riel@surriel.com>

Acked-by: Michal Hocko <mhocko@suse.com>

Although I would rephrased this a bit
> + * PG_swapbacked is cleared if the page is page cache page backed by a regular
> + * file system or anonymous page lazily freed (e.g. via MADV_FREE).  It is set
> + * if the page is normal anonymous page, tmpfs or otherwise RAM or swap backed.
> + *

PG_swapbacked is set when a page uses swap as a backing storage. This
are usually PageAnon or shmem pages but please note that even anonymous
pages might lose their PG_swapbacked flag when they simply can be
dropped (e.g. as a result of MADV_FREE).
-- 
Michal Hocko
SUSE Labs