From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 0F5786B004D for ; Thu, 28 May 2009 10:49:56 -0400 (EDT) Date: Thu, 28 May 2009 22:50:21 +0800 From: Wu Fengguang Subject: Re: [PATCH] [13/16] HWPOISON: The high level memory error handler in the VM v3 Message-ID: <20090528145021.GA5503@localhost> References: <200905271012.668777061@firstfloor.org> <20090527201239.C2C9C1D0294@basil.firstfloor.org> <20090528082616.GG6920@wotan.suse.de> <20090528093141.GD1065@one.firstfloor.org> <20090528120854.GJ6920@wotan.suse.de> <20090528134520.GH1065@one.firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090528134520.GH1065@one.firstfloor.org> Sender: owner-linux-mm@kvack.org To: Andi Kleen Cc: Nick Piggin , "hugh@veritas.com" , "riel@redhat.com" , "akpm@linux-foundation.org" , "chris.mason@oracle.com" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" List-ID: On Thu, May 28, 2009 at 09:45:20PM +0800, Andi Kleen wrote: > On Thu, May 28, 2009 at 02:08:54PM +0200, Nick Piggin wrote: [snip] > > > > BTW. I don't know if you are checking for PG_writeback often enough? > > You can't remove a PG_writeback page from pagecache. The normal > > pattern is lock_page(page); wait_on_page_writeback(page); which I > > So pages can be in writeback without being locked? I still > wasn't able to find such a case (in fact unless I'm misreading > the code badly the writeback bit is only used by NFS and a few > obscure cases) Yes the writeback page is typically not locked. Only read IO requires to be exclusive. Read IO is in fact page *writer*, while writeback IO is page *reader* :-) The writeback bit is _widely_ used. test_set_page_writeback() is directly used by NFS/AFS etc. But its main user is in fact set_page_writeback(), which is called in 26 places. > > think would be safest > > Okay. I'll just add it after the page lock. > > > (then you never have to bother with the writeback bit again) > > Until Fengguang does something fancy with it. Yes I'm going to do it without wait_on_page_writeback(). The reason truncate_inode_pages_range() has to wait on writeback page is to ensure data integrity. Otherwise if there comes two events: truncate page A at offset X populate page B at offset X If A and B are all writeback pages, then B can hit disk first and then be overwritten by A. Which corrupts the data at offset X from user's POV. But for hwpoison, there are no such worries. If A is poisoned, we do our best to isolate it as well as intercepting its IO. If the interception fails, it will trigger another machine check before hitting the disk. After all, poisoned A means the data at offset X is already corrupted. It doesn't matter if there comes another B page. 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