From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id B58BB6B00B5 for ; Sun, 19 Dec 2010 22:31:57 -0500 (EST) Received: by iwn40 with SMTP id 40so2825222iwn.14 for ; Sun, 19 Dec 2010 19:31:55 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20101220120218.E56F.A69D9226@jp.fujitsu.com> References: <20101220113239.E56C.A69D9226@jp.fujitsu.com> <20101220120218.E56F.A69D9226@jp.fujitsu.com> Date: Mon, 20 Dec 2010 12:31:55 +0900 Message-ID: Subject: Re: [RFC 5/5] truncate: Remove unnecessary page release From: Minchan Kim Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: Andrew Morton , linux-mm , LKML , Nick Piggin , Al Viro , Andi Kleen List-ID: On Mon, Dec 20, 2010 at 12:03 PM, KOSAKI Motohiro wrote: >> On Mon, Dec 20, 2010 at 11:32 AM, KOSAKI Motohiro >> wrote: >> >> On Mon, Dec 20, 2010 at 11:21 AM, KOSAKI Motohiro >> >> wrote: >> >> >> This patch series changes remove_from_page_cache's page ref counti= ng >> >> >> rule. page cache ref count is decreased in remove_from_page_cache. >> >> >> So we don't need call again in caller context. >> >> >> >> >> >> Cc: Nick Piggin >> >> >> Cc: Al Viro >> >> >> Cc: linux-mm@kvack.org >> >> >> Signed-off-by: Minchan Kim >> >> >> --- >> >> >> =A0mm/truncate.c | =A0 =A01 - >> >> >> =A01 files changed, 0 insertions(+), 1 deletions(-) >> >> >> >> >> >> diff --git a/mm/truncate.c b/mm/truncate.c >> >> >> index 9ee5673..8decb93 100644 >> >> >> --- a/mm/truncate.c >> >> >> +++ b/mm/truncate.c >> >> >> @@ -114,7 +114,6 @@ truncate_complete_page(struct address_space *m= apping, struct page *page) >> >> >> =A0 =A0 =A0 =A0* calls cleancache_put_page (and note page->mapping= is now NULL) >> >> >> =A0 =A0 =A0 =A0*/ >> >> >> =A0 =A0 =A0 cleancache_flush_page(mapping, page); >> >> >> - =A0 =A0 page_cache_release(page); =A0 =A0 =A0 /* pagecache ref *= / >> >> >> =A0 =A0 =A0 return 0; >> >> > >> >> > Do we _always_ have stable page reference here? IOW, I can assume >> >> >> >> I think so. >> >> Because the page is locked so caller have to hold a ref to unlock it. >> > >> > Hmm... >> > >> > Perhaps, I'm missing something. But I think =A0__memory_failure() only= lock >> > compaund_head page. not all. example. >> >> The page passed truncate_complete_page is only head page? >> Is it possible to pass the page which isn't head of compound in >> truncate_complete_page? > > I dunno, really. My five miniture grep found following logic. therefore I= asked you. > > > > __memory_failure() > { > =A0 =A0 =A0 =A0p =3D pfn_to_page(pfn); > =A0 =A0 =A0 =A0hpage =3D compound_head(p); > (snip) > =A0 =A0 =A0 =A0res =3D -EBUSY; > =A0 =A0 =A0 =A0for (ps =3D error_states;; ps++) { > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if ((p->flags & ps->mask) =3D=3D ps->res) = { > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0res =3D page_action(ps, p,= pfn); =A0// call truncate here > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0break; > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0} > =A0 =A0 =A0 =A0} > out: > =A0 =A0 =A0 =A0unlock_page(hpage); > } > > AFAIK, We have to handle head page when we handle compound page. Internal page handling logic about tail pages is hidden by compound page internal. So I think memory_failure also don't have a problem. For needing double check, Cced Andi. Thanks for the review, KOSAKI. --=20 Kind regards, Minchan Kim -- 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/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org