From: Fengguang Wu <fengguang.wu@intel.com>
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: David Rientjes <rientjes@google.com>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
Andrew Morton <akpm@linux-foundation.org>,
Andi Kleen <andi.kleen@intel.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] pagemap: fix wrong KPF_THP on slab pages
Date: Wed, 26 Sep 2012 15:38:41 +0800 [thread overview]
Message-ID: <20120926073841.GA26028@localhost> (raw)
In-Reply-To: <1348639568-10648-1-git-send-email-n-horiguchi@ah.jp.nec.com>
On Wed, Sep 26, 2012 at 02:06:08AM -0400, Naoya Horiguchi wrote:
> On Wed, Sep 26, 2012 at 12:02:34AM -0400, Naoya Horiguchi wrote:
> ...
> > > > + * page is a thp, not a non-huge compound page.
> > > > + */
> > > > + else if (PageTransCompound(page) && !PageSlab(page))
> > > > u |= 1 << KPF_THP;
> > >
> > > Good catch!
> > >
> > > Will this report THP for the various drivers that do __GFP_COMP
> > > page allocations?
> >
> > I'm afraid it will. I think of checking PageLRU as an alternative,
> > but it needs compound_head() to report tail pages correctly.
> > In this context, pages are not pinned or locked, so it's unsafe to
> > use compound_head() because it can return a dangling pointer.
> > Maybe it's a thp's/hugetlbfs's (not kpageflags specific) problem,
> > so going forward with compound_head() expecting that it will be
> > fixed in the future work can be an option.
>
> It seems that compound_trans_head() solves this problem, so I'll
> simply use it.
Naoya, in fact I didn't quite catch your concerns. Why not just test
PageTransCompound(page) && PageLRU(page)
The whole page flag report thing is inherently racy and it's fine to
report wrong values due to races. The "__GFP_COMP reported as THP",
however, should be avoided because it will make consistent wrong
reporting of page flags.
Thanks,
Fengguang
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next prev parent reply other threads:[~2012-09-26 7:38 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-25 13:56 [PATCH] pagemap: fix wrong KPF_THP on slab pages Naoya Horiguchi
2012-09-25 15:59 ` KOSAKI Motohiro
2012-09-25 17:05 ` Naoya Horiguchi
2012-09-25 19:03 ` KOSAKI Motohiro
2012-09-26 0:20 ` David Rientjes
2012-09-26 2:06 ` Naoya Horiguchi
2012-09-26 2:26 ` David Rientjes
2012-09-26 2:47 ` Fengguang Wu
2012-09-26 4:02 ` Naoya Horiguchi
2012-09-26 6:06 ` Naoya Horiguchi
2012-09-26 7:38 ` Fengguang Wu [this message]
2012-09-26 14:42 ` Naoya Horiguchi
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