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Date: Wed, 9 Sep 2020 08:43:38 -0700
From: Alexander Duyck <alexander.duyck@...il.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Alex Shi <alex.shi@...ux.alibaba.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Mel Gorman <mgorman@...hsingularity.net>,
Tejun Heo <tj@...nel.org>, Hugh Dickins <hughd@...gle.com>,
Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
Daniel Jordan <daniel.m.jordan@...cle.com>,
Johannes Weiner <hannes@...xchg.org>,
kbuild test robot <lkp@...el.com>,
linux-mm <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>, cgroups@...r.kernel.org,
Shakeel Butt <shakeelb@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Wei Yang <richard.weiyang@...il.com>,
"Kirill A. Shutemov" <kirill@...temov.name>,
Rong Chen <rong.a.chen@...el.com>,
Michal Hocko <mhocko@...e.com>,
Vladimir Davydov <vdavydov.dev@...il.com>, shy828301@...il.com,
Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Subject: Re: [PATCH v18 31/32] mm: Add explicit page decrement in exception
path for isolate_lru_pages
On Tue, Sep 8, 2020 at 6:01 PM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Mon, Aug 24, 2020 at 08:55:04PM +0800, Alex Shi wrote:
> > +++ b/mm/vmscan.c
> > @@ -1688,10 +1688,13 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> >
> > if (!TestClearPageLRU(page)) {
> > /*
> > - * This page may in other isolation path,
> > - * but we still hold lru_lock.
> > + * This page is being isolated in another
> > + * thread, but we still hold lru_lock. The
> > + * other thread must be holding a reference
> > + * to the page so this should never hit a
> > + * reference count of 0.
> > */
> > - put_page(page);
> > + WARN_ON(put_page_testzero(page));
> > goto busy;
>
> I read Hugh's review and that led me to take a look at this. We don't
> do it like this. Use the same pattern as elsewhere in mm:
>
> page_ref_sub(page, nr);
> VM_BUG_ON_PAGE(page_count(page) <= 0, page);
>
>
Actually for this case page_ref_dec(page) would make more sense
wouldn't it? Otherwise I agree that would be a better change if that
is the way it has been handled before. I just wasn't familiar with
those other spots.
Thanks.
- Alex
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