From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from westrelay02.boulder.ibm.com (westrelay02.boulder.ibm.com [9.17.195.11]) by e34.co.us.ibm.com (8.12.11.20060308/8.12.11) with ESMTP id k71FtXra014770 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=FAIL) for ; Tue, 1 Aug 2006 11:55:33 -0400 Received: from d03av01.boulder.ibm.com (d03av01.boulder.ibm.com [9.17.195.167]) by westrelay02.boulder.ibm.com (8.13.6/NCO/VER7.0) with ESMTP id k71FtVp5132912 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Tue, 1 Aug 2006 09:55:32 -0600 Received: from d03av01.boulder.ibm.com (loopback [127.0.0.1]) by d03av01.boulder.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id k71FtUCa029507 for ; Tue, 1 Aug 2006 09:55:30 -0600 Subject: Re: [patch 1/2] mm: speculative get_page From: Dave Kleikamp In-Reply-To: <20060801193203.GA191@oleg> References: <20060801193203.GA191@oleg> Content-Type: text/plain Date: Tue, 01 Aug 2006 10:55:29 -0500 Message-Id: <1154447729.10401.16.camel@kleikamp.austin.ibm.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Oleg Nesterov Cc: Nick Piggin , Hugh Dickins , Andrew Morton , Andy Whitcroft , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Tue, 2006-08-01 at 23:32 +0400, Oleg Nesterov wrote: > Nick Piggin wrote: > > > > --- linux-2.6.orig/mm/vmscan.c > > +++ linux-2.6/mm/vmscan.c > > @@ -380,6 +380,8 @@ int remove_mapping(struct address_space > > if (!mapping) > > return 0; /* truncate got there first */ > > > > + SetPageNoNewRefs(page); > > + smp_wmb(); > > write_lock_irq(&mapping->tree_lock); > > > > Is it enough? > > PG_nonewrefs could be already set by another add_to_page_cache()/remove_mapping(), > and it will be cleared when we take ->tree_lock. Isn't the page locked when calling remove_mapping()? It looks like SetPageNoNewRefs & ClearPageNoNewRefs are called in safe places. Either the page is locked, or it's newly allocated. I could have missed something, though. > For example: > > CPU_0 CPU_1 CPU_3 > > add_to_page_cache: > > SetPageNoNewRefs(); > write_lock_irq(->tree_lock); SetPageLocked(page); > ... > write_unlock_irq(->tree_lock); > > remove_mapping: > > SetPageNoNewRefs(); > > ClearPageNoNewRefs(); > write_lock_irq(->tree_lock); > > check page_count() > > page_cache_get_speculative: > > increment page_count() > > no PG_nonewrefs => return > > Oleg. Shaggy -- David Kleikamp IBM Linux Technology Center -- 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