From: Chris Mason Subject: Re: [PATCH RFC] ext3 data=guarded v5 Date: Wed, 29 Apr 2009 16:37:01 -0400 Message-ID: <1241037421.20099.70.camel@think.oraclecorp.com> References: <1240941840.15136.44.camel@think.oraclecorp.com> <20090429085632.GA18273@duck.suse.cz> <1241014093.20099.28.camel@think.oraclecorp.com> <20090429191533.GB22936@duck.suse.cz> <1241034089.20099.60.camel@think.oraclecorp.com> <20090429200412.GA27924@duck.suse.cz> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: Linus Torvalds , "Theodore Ts'o" , Linux Kernel Developers List , Ext4 Developers List , Mike Galbraith To: Jan Kara Return-path: Received: from acsinet12.oracle.com ([141.146.126.234]:30746 "EHLO acsinet12.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751730AbZD2UiF (ORCPT ); Wed, 29 Apr 2009 16:38:05 -0400 In-Reply-To: <20090429200412.GA27924@duck.suse.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed, 2009-04-29 at 22:04 +0200, Jan Kara wrote: > > What we don't want to do is have a call to write() over existing blocks > > in the file add new things to the data=ordered list. I don't see how we > > can avoid that without datanew. > Yes, what I suggest would do exactly that: > In ordered_writepage() in the beginning we do: > page_bufs = page_buffers(page); > if (!walk_page_buffers(NULL, page_bufs, 0, PAGE_CACHE_SIZE, > NULL, buffer_unmapped)) { > return block_write_full_page(page, NULL, wbc); > } > So we only get to starting a transaction and file some buffers if some buffer > in the page is unmapped. Write() maps / allocates all buffers in write_begin() > so they are never added to ordered lists in writepage(). Right, writepage doesn't really need datanew. > We rely on write_end > to do it. So the only case where not all buffers in the page are mapped is > when we have to allocate in writepage() (mmaped write) or the two cases I > describe above. But I still think write_end does need datanew. That's where 99% of the ordered buffers are going to come from when we overwrite the contents of an existing file. -chris