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From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@kernel.org>, linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Oscar Salvador <OSalvador@suse.com>,
	Pavel Tatashin <pasha.tatashin@oracle.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 15:33:07 +0100	[thread overview]
Message-ID: <8e85a64b-2c8f-52f7-bd46-9463d6202806@redhat.com> (raw)
In-Reply-To: <20181120134323.13007-4-mhocko@kernel.org>

On 20.11.18 14:43, 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>
> ---
>  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;
>  
> 

Right, no sense in referencing a page if we know we will drop the
reference right away.

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 

Thanks,

David / dhildenb

  parent reply	other threads:[~2018-11-20 14:33 UTC|newest]

Thread overview: 31+ 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 ` 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 13:43   ` 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 13:43   ` 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 13:43   ` 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 [this message]
2018-11-21  1:47   ` Hugh Dickins
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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