Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262044AbUKVKug (ORCPT ); Mon, 22 Nov 2004 05:50:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262040AbUKVKuX (ORCPT ); Mon, 22 Nov 2004 05:50:23 -0500 Received: from fw.osdl.org ([65.172.181.6]:53228 "EHLO mail.osdl.org") by vger.kernel.org with ESMTP id S262053AbUKVKmC (ORCPT ); Mon, 22 Nov 2004 05:42:02 -0500 Date: Mon, 22 Nov 2004 02:41:45 -0800 From: Andrew Morton To: OGAWA Hirofumi Cc: torvalds@osdl.org, linux-kernel@vger.kernel.org Subject: Re: [RFC][PATCH] problem of cont_prepare_write() Message-Id: <20041122024145.5baaa0b0.akpm@osdl.org> In-Reply-To: <877joexjk5.fsf@devron.myhome.or.jp> References: <877joexjk5.fsf@devron.myhome.or.jp> X-Mailer: Sylpheed version 0.9.7 (GTK+ 1.2.10; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1666 Lines: 46 OGAWA Hirofumi wrote: > > If I do the following operation on fatfs, and my box under heavy load, > > open("testfile", O_CREAT | O_TRUNC | O_RDWR, 0664); > lseek(fd, 500*1024*1024 - 1, SEEK_SET); > write(fd, "\0", 1); > > In cont_prepare_write(), kernel fills the hole by zero cleared page. > > fs/buffer.c:cont_prepare_write:2210, > while(page->index > (pgpos = *bytes>>PAGE_CACHE_SHIFT)) { > > [...] > > status = __block_prepare_write(inode, new_page, zerofrom, > PAGE_CACHE_SIZE, get_block); > if (status) > goto out_unmap; > kaddr = kmap_atomic(new_page, KM_USER0); > memset(kaddr+zerofrom, 0, PAGE_CACHE_SIZE-zerofrom); > flush_dcache_page(new_page); > kunmap_atomic(kaddr, KM_USER0); > __block_commit_write(inode, new_page, > zerofrom, PAGE_CACHE_SIZE); > unlock_page(new_page); > page_cache_release(new_page); > } > > But until ->commit_write(), kernel doesn't update the ->i_size. Then, > if kernel writes out that hole page before updates of ->i_size, dirty > flag of buffer_head is cleared in __block_write_full_page(). So hole > page was not writed to disk. But the page remains locked across both the ->prepare_write() and ->commit_write() operations. So writeback cannot get in there to call ->writepage(). The page lock should correctly synchronise the prepare_write/commit_write and writeback functions. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/