From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx147.postini.com [74.125.245.147]) by kanga.kvack.org (Postfix) with SMTP id A815B6B002B for ; Tue, 25 Sep 2012 22:48:27 -0400 (EDT) Date: Wed, 26 Sep 2012 10:47:54 +0800 From: Fengguang Wu Subject: Re: [PATCH] pagemap: fix wrong KPF_THP on slab pages Message-ID: <20120926024754.GA12716@localhost> References: <1348625168-28983-1-git-send-email-n-horiguchi@ah.jp.nec.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1348625168-28983-1-git-send-email-n-horiguchi@ah.jp.nec.com> Sender: owner-linux-mm@kvack.org List-ID: To: Naoya Horiguchi Cc: David Rientjes , KOSAKI Motohiro , Andrew Morton , Andi Kleen , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue, Sep 25, 2012 at 10:06:08PM -0400, Naoya Horiguchi wrote: > On Tue, Sep 25, 2012 at 05:20:48PM -0700, David Rientjes wrote: > > On Tue, 25 Sep 2012, Naoya Horiguchi wrote: > > > > > KPF_THP can be set on non-huge compound pages like slab pages, because > > > PageTransCompound only sees PG_head and PG_tail. Obviously this is a bug > > > and breaks user space applications which look for thp via /proc/kpageflags. > > > Currently thp is constructed only on anonymous pages, so this patch makes > > > KPF_THP be set when both of PageAnon and PageTransCompound are true. > > > > > > Changelog in v2: > > > - add a comment in code > > > > > > Signed-off-by: Naoya Horiguchi > > > > Wouldn't PageTransCompound(page) && !PageHuge(page) && !PageSlab(page) be > > better for a future extension of thp support? > > Yes, this saves us an additional change when thp starts handling pagecaches. > Andrew, can you replace the previous version in -mm tree with new one below? > > Thanks, > Naoya > --- > From: Naoya Horiguchi > Date: Tue, 25 Sep 2012 21:30:25 -0400 > Subject: [PATCH v3] kpageflags: fix wrong KPF_THP on slab pages > > KPF_THP can be set on non-huge compound pages like slab pages, because > PageTransCompound only sees PG_head and PG_tail. Obviously this is a bug s/sees/checks/ > and breaks user space applications which look for thp via /proc/kpageflags. > This patch rules out setting KPF_THP wrongly by additional PageSlab check. > > Changelog in v3: > - check PageSlab instead of PageAnon > - fix patch subject > > Changelog in v2: > - add a comment in code > > Signed-off-by: Naoya Horiguchi > --- > fs/proc/page.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/fs/proc/page.c b/fs/proc/page.c > index 7fcd0d6..e36d1f3 100644 > --- a/fs/proc/page.c > +++ b/fs/proc/page.c > @@ -115,7 +115,12 @@ u64 stable_page_flags(struct page *page) > u |= 1 << KPF_COMPOUND_TAIL; > if (PageHuge(page)) > u |= 1 << KPF_HUGE; > - else if (PageTransCompound(page)) > + /* > + * PageTransCompound can be true for slab pages because it just sees s/sees/checks/ > + * PG_head/PG_head, so we need to check PageSlab to make sure the given PG_head/PG_head should be PG_head/PG_tail. > + * 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? Thanks, Fengguang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org