From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx170.postini.com [74.125.245.170]) by kanga.kvack.org (Postfix) with SMTP id 0FC0E6B006C for ; Tue, 2 Apr 2013 20:14:04 -0400 (EDT) Date: Wed, 3 Apr 2013 09:14:01 +0900 From: Minchan Kim Subject: Re: [PATCH] THP: Use explicit memory barrier Message-ID: <20130403001401.GC16026@blaptop> References: <1364773535-26264-1-git-send-email-minchan@kernel.org> <20130402003746.GA30444@blaptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: David Rientjes , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mel Gorman , Andrea Arcangeli , Kamezawa Hiroyuki , Peter Zijlstra On Tue, Apr 02, 2013 at 12:30:15PM -0700, Hugh Dickins wrote: > On Tue, 2 Apr 2013, Minchan Kim wrote: > > On Mon, Apr 01, 2013 at 04:35:38PM -0700, David Rientjes wrote: > > > On Mon, 1 Apr 2013, Minchan Kim wrote: > > > > > > > __do_huge_pmd_anonymous_page depends on page_add_new_anon_rmap's > > > > spinlock for making sure that clear_huge_page write become visible > > > > after set set_pmd_at() write. > > > > > > > > But lru_cache_add_lru uses pagevec so it could miss spinlock > > > > easily so above rule was broken so user may see inconsistent data. > > > > > > > > This patch fixes it with using explict barrier rather than depending > > > > on lru spinlock. > > > > > > > > > > Is this the same issue that Andrea responded to in the "thp and memory > > > barrier assumptions" thread at http://marc.info/?t=134333512700004 ? > > > > Yes and Peter pointed out further step. > > Thanks for pointing out. > > Not that I know that Andrea alreay noticed it, I don't care about this > > patch. > > > > Remaining question is Kame's one. > > > Hmm...how about do_anonymous_page() ? there are no comments/locks/barriers. > > > Users can see non-zero value after page fault in theory ? > > Isn't there anyone could answer it? > > See Nick's 2008 0ed361dec "mm: fix PageUptodate data race", which gave us > > static inline void __SetPageUptodate(struct page *page) > { > smp_wmb(); > __set_bit(PG_uptodate, &(page)->flags); > } > > So both do_anonymous_page() and __do_huge_pmd_anonymous_page() look safe > to me already, though the huge_memory one could do with a fixed comment. Thanks you very much! That's one everybody are really missing. Here it goes! ==================== 8< =====================