From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754050AbZFAAZ6 (ORCPT ); Sun, 31 May 2009 20:25:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752668AbZFAAZu (ORCPT ); Sun, 31 May 2009 20:25:50 -0400 Received: from serv2.oss.ntt.co.jp ([222.151.198.100]:59781 "EHLO serv2.oss.ntt.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752631AbZFAAZt (ORCPT ); Sun, 31 May 2009 20:25:49 -0400 Message-Id: <6.0.0.20.2.20090529142527.071669e0@172.19.0.2> X-Mailer: QUALCOMM Windows Eudora Version 6J-Jr3 Date: Fri, 29 May 2009 14:35:55 +0900 To: Andrew Morton From: Hisashi Hifumi Subject: [RESEND] [PATCH] readahead:add blk_run_backing_dev Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Andrew. I added blk_run_backing_dev on page_cache_async_readahead so readahead I/O is unpluged to improve throughput on especially RAID environment. The normal case is, if page N become uptodate at time T(N), then T(N) <= T(N+1) holds. With RAID (and NFS to some degree), there is no strict ordering, the data arrival time depends on runtime status of individual disks, which breaks that formula. So in do_generic_file_read(), just after submitting the async readahead IO request, the current page may well be uptodate, so the page won't be locked, and the block device won't be implicitly unplugged: if (PageReadahead(page)) page_cache_async_readahead() if (!PageUptodate(page)) goto page_not_up_to_date; //... page_not_up_to_date: lock_page_killable(page); Therefore explicit unplugging can help. Following is the test result with dd. #dd if=testdir/testfile of=/dev/null bs=16384 -2.6.30-rc6 1048576+0 records in 1048576+0 records out 17179869184 bytes (17 GB) copied, 224.182 seconds, 76.6 MB/s -2.6.30-rc6-patched 1048576+0 records in 1048576+0 records out 17179869184 bytes (17 GB) copied, 206.465 seconds, 83.2 MB/s (7Disks RAID-0 Array) -2.6.30-rc6 1054976+0 records in 1054976+0 records out 17284726784 bytes (17 GB) copied, 212.233 seconds, 81.4 MB/s -2.6.30-rc6-patched 1054976+0 records out 17284726784 bytes (17 GB) copied, 198.878 seconds, 86.9 MB/s (7Disks RAID-5 Array) Thanks. Signed-off-by: Hisashi Hifumi Acked-by: Wu Fengguang mm/readahead.c | 10 ++++++++++ 1 file changed, 10 insertions(+) --- linux.orig/mm/readahead.c +++ linux/mm/readahead.c @@ -490,5 +490,15 @@ page_cache_async_readahead(struct addres /* do read-ahead */ ondemand_readahead(mapping, ra, filp, true, offset, req_size); + + /* + * Normally the current page is !uptodate and lock_page() will be + * immediately called to implicitly unplug the device. However this + * is not always true for RAID conifgurations, where data arrives + * not strictly in their submission order. In this case we need to + * explicitly kick off the IO. + */ + if (PageUptodate(page)) + blk_run_backing_dev(mapping->backing_dev_info, NULL); } EXPORT_SYMBOL_GPL(page_cache_async_readahead);