From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id E95359000C1 for ; Tue, 26 Apr 2011 10:36:51 -0400 (EDT) Date: Tue, 26 Apr 2011 22:36:47 +0800 From: Wu Fengguang Subject: [PATCH 3/3 with new changelog] readahead: trigger mmap sequential readahead on PG_readahead Message-ID: <20110426143647.GA14604@localhost> References: <20110426094352.030753173@intel.com> <20110426094859.591091128@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110426094859.591091128@intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton , Andi Kleen Cc: "Chen, Tim C" , "Li, Shaohua" , LKML , Linux Memory Management List Previously the mmap sequential readahead is triggered by updating ra->prev_pos on each page fault and compare it with current page offset. In the mosbench exim benchmark which does multi-threaded page faults on shared struct file, the ra->mmap_miss and ra->prev_pos updates are found to cause excessive cache line bouncing on tmpfs, which actually disabled readahead totally (shmem_backing_dev_info.ra_pages == 0). So remove the ra->prev_pos recording, and instead tag PG_readahead to trigger the possible sequential readahead. It's not only more simple, but also will work more reliably on concurrent reads on shared struct file. Tested-by: Tim Chen Reported-by: Andi Kleen Signed-off-by: Wu Fengguang --- mm/filemap.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) --- linux-next.orig/mm/filemap.c 2011-04-23 16:52:21.000000000 +0800 +++ linux-next/mm/filemap.c 2011-04-24 09:59:08.000000000 +0800 @@ -1531,8 +1531,7 @@ static void do_sync_mmap_readahead(struc if (!ra->ra_pages) return; - if (VM_SequentialReadHint(vma) || - offset - 1 == (ra->prev_pos >> PAGE_CACHE_SHIFT)) { + if (VM_SequentialReadHint(vma)) { page_cache_sync_readahead(mapping, ra, file, offset, ra->ra_pages); return; @@ -1555,7 +1554,7 @@ static void do_sync_mmap_readahead(struc ra_pages = max_sane_readahead(ra->ra_pages); ra->start = max_t(long, 0, offset - ra_pages / 2); ra->size = ra_pages; - ra->async_size = 0; + ra->async_size = ra_pages / 4; ra_submit(ra, mapping, file); } @@ -1661,7 +1660,6 @@ retry_find: return VM_FAULT_SIGBUS; } - ra->prev_pos = (loff_t)offset << PAGE_CACHE_SHIFT; vmf->page = page; return ret | VM_FAULT_LOCKED; -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org