linux-kernel - Re: [RFC PATCH 3/3] mm, fault_around: do not take a reference to a locked page

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Message-ID: <20181120142559.GM22247@dhcp22.suse.cz>
Date:   Tue, 20 Nov 2018 15:25:59 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <OSalvador@...e.com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        David Hildenbrand <david@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 3/3] mm, fault_around: do not take a reference to a
 locked page

On Tue 20-11-18 17:17:00, Kirill A. Shutemov wrote:
> On Tue, Nov 20, 2018 at 03:12:07PM +0100, Michal Hocko wrote:
> > On Tue 20-11-18 17:07:15, Kirill A. Shutemov wrote:
> > > On Tue, Nov 20, 2018 at 02:43:23PM +0100, Michal Hocko wrote:
> > > > From: Michal Hocko <mhocko@...e.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.
> > > 
> > > Looks fine to me.
> > 
> > Thanks for the review.
> > 
> > > But please drop a line of comment in the code. As is it might be confusing
> > > for a reader.
> > 
> > This?
> 
> Yep.
> 
> Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

Cool, thanks! I will wait some more time for review feedback for other
patches and then repost with this folded in.

-- 
Michal Hocko
SUSE Labs