From: Matthew Wilcox <willy@infradead.org>
To: chenqiwu <qiwuchen55@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>,
akpm@linux-foundation.org, linux-mm@kvack.org,
chenqiwu <chenqiwu@xiaomi.com>
Subject: Re: [PATCH] mm/memory: add refcount for special mapping page in copy_one_pte()
Date: Fri, 17 Apr 2020 07:45:38 -0700 [thread overview]
Message-ID: <20200417144538.GM5820@bombadil.infradead.org> (raw)
In-Reply-To: <20200417142618.GA31882@cqw-OptiPlex-7050>
On Fri, Apr 17, 2020 at 10:26:18PM +0800, chenqiwu wrote:
> On Fri, Apr 17, 2020 at 01:43:12PM +0200, Michal Hocko wrote:
> > On Fri 17-04-20 18:31:54, qiwuchen55@gmail.com wrote:
> > > From: chenqiwu <chenqiwu@xiaomi.com>
> > >
> > > If we get a special mapping page like device mapping page or zero page
> > > when copy_one_pte, it's necessary add the page refcount count.
> >
> > From the changelog it is not clear what is the actual problem and how
> > the patch address it. Please be more verbose.
> >
> I don't find any actual problem, but I think there should be addressed
> to update the page refcount for special mappings include devmap and zero
> page instead of doing nothing else, since we copy the pte from one task
> to the other.
But the zero page is special. It's never freed. So unless we're seeing
a refcount problem with the zero page, I would suggest that your patch
is eventually going to overflow the refcount on the zero page.
next prev parent reply other threads:[~2020-04-17 14:45 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-17 10:31 qiwuchen55
2020-04-17 11:43 ` Michal Hocko
2020-04-17 14:26 ` chenqiwu
2020-04-17 14:45 ` Matthew Wilcox [this message]
2020-04-17 15:23 ` Michal Hocko
2020-04-18 3:12 ` chenqiwu
2020-04-20 7:42 ` Michal Hocko
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