linux-kernel - Re: [PATCH -mm v6 5/6] proc: add kpageidle file

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Date:	Sat, 11 Jul 2015 17:53:38 +0300
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Andres Lagar-Cavilla <andreslc@...gle.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Greg Thelen <gthelen@...gle.com>,
	Michel Lespinasse <walken@...gle.com>,
	David Rientjes <rientjes@...gle.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Jonathan Corbet <corbet@....net>, <linux-api@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <linux-mm@...ck.org>,
	<cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -mm v6 5/6] proc: add kpageidle file

On Thu, Jul 09, 2015 at 04:19:00PM +0300, Vladimir Davydov wrote:
> On Wed, Jul 08, 2015 at 04:01:13PM -0700, Andres Lagar-Cavilla wrote:
> > On Fri, Jun 12, 2015 at 2:52 AM, Vladimir Davydov
> > > +#ifdef CONFIG_IDLE_PAGE_TRACKING
> > > +/*
> > > + * Idle page tracking only considers user memory pages, for other types of
> > > + * pages the idle flag is always unset and an attempt to set it is silently
> > > + * ignored.
> > > + *
> > > + * We treat a page as a user memory page if it is on an LRU list, because it is
> > > + * always safe to pass such a page to page_referenced(), which is essential for
> > > + * idle page tracking. With such an indicator of user pages we can skip
> > > + * isolated pages, but since there are not usually many of them, it will hardly
> > > + * affect the overall result.
> > > + *
> > > + * This function tries to get a user memory page by pfn as described above.
> > > + */
> > > +static struct page *kpageidle_get_page(unsigned long pfn)
> > > +{
> > > +       struct page *page;
> > > +       struct zone *zone;
> > > +
> > > +       if (!pfn_valid(pfn))
> > > +               return NULL;
> > > +
> > > +       page = pfn_to_page(pfn);
> > > +       if (!page || !PageLRU(page))
> > 
> > Isolation can race in while you're processing the page, after these
> > checks. This is ok, but worth a small comment.
> 
> Agree, will add one.

Oh, the comment is already present - it's in the description to this
function. Minchan asked me to add it long time ago, and so I did.
Completely forgot about it.

Thanks,
Vladimir
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