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From: Hugh Dickins <hughd@google.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
	Oscar Salvador <OSalvador@suse.com>,
	Pavel Tatashin <pasha.tatashin@oracle.com>,
	David Hildenbrand <david@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Michal Hocko <mhocko@suse.com>,
	"Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: [RFC PATCH 3/3] mm, fault_around: do not take a reference to a locked page
Date: Tue, 20 Nov 2018 17:47:21 -0800 (PST)	[thread overview]
Message-ID: <alpine.LSU.2.11.1811201721470.2061@eggly.anvils> (raw)
In-Reply-To: <20181120134323.13007-4-mhocko@kernel.org>

On Tue, 20 Nov 2018, Michal Hocko wrote:

> From: Michal Hocko <mhocko@suse.com>
> 
> filemap_map_pages takes a speculative reference to each page in the
> range before it tries to lock that page. While this is correct it
> also can influence page migration which will bail out when seeing
> an elevated reference count. The faultaround code would bail on
> seeing a locked page so we can pro-actively check the PageLocked
> bit before page_cache_get_speculative and prevent from pointless
> reference count churn.
> 
> Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
> Suggested-by: Jan Kara <jack@suse.cz>
> Signed-off-by: Michal Hocko <mhocko@suse.com>

Acked-by: Hugh Dickins <hughd@google.com>

though I think this patch is more useful to the avoid atomic ops,
and unnecessary dirtying of the cacheline, than to avoid the very
transient elevation of refcount, which will not affect page migration
very much.

> ---
>  mm/filemap.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 81adec8ee02c..c76d6a251770 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2553,6 +2553,9 @@ void filemap_map_pages(struct vm_fault *vmf,
>  			goto next;
>  
>  		head = compound_head(page);
> +
> +		if (PageLocked(head))
> +			goto next;
>  		if (!page_cache_get_speculative(head))
>  			goto next;
>  
> -- 
> 2.19.1

  parent reply	other threads:[~2018-11-21  1:47 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-20 13:43 [RFC PATCH 0/3] few memory offlining enhancements Michal Hocko
2018-11-20 13:43 ` [RFC PATCH 1/3] mm, memory_hotplug: try to migrate full section worth of pages Michal Hocko
2018-11-20 14:18   ` David Hildenbrand
2018-11-20 14:25     ` Michal Hocko
2018-11-20 14:27       ` David Hildenbrand
2018-11-20 14:33   ` Pavel Tatashin
2018-11-20 14:51   ` osalvador
2018-11-20 15:00     ` Michal Hocko
2018-11-20 13:43 ` [RFC PATCH 2/3] mm, memory_hotplug: deobfuscate migration part of offlining Michal Hocko
2018-11-20 14:26   ` David Hildenbrand
2018-11-20 14:34     ` Michal Hocko
2018-11-20 14:34       ` David Hildenbrand
2018-11-20 15:13   ` osalvador
2018-11-20 15:18     ` Michal Hocko
2018-11-20 13:43 ` [RFC PATCH 3/3] mm, fault_around: do not take a reference to a locked page Michal Hocko
2018-11-20 14:07   ` Kirill A. Shutemov
2018-11-20 14:12     ` Michal Hocko
2018-11-20 14:17       ` Kirill A. Shutemov
2018-11-20 14:25         ` Michal Hocko
2018-11-21  4:51       ` William Kucharski
2018-11-21  7:07         ` Michal Hocko
2018-11-20 14:33   ` David Hildenbrand
2018-11-21  1:47   ` Hugh Dickins [this message]
2018-11-21  7:11     ` Michal Hocko
2018-11-22  2:27       ` Hugh Dickins
2018-11-22  9:05         ` Michal Hocko
2018-11-23 20:22           ` Hugh Dickins

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