Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762807AbXEPWtX (ORCPT ); Wed, 16 May 2007 18:49:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759256AbXEPWsg (ORCPT ); Wed, 16 May 2007 18:48:36 -0400 Received: from smtp.ustc.edu.cn ([202.38.64.16]:50146 "HELO ustc.edu.cn" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with SMTP id S1758480AbXEPWsd (ORCPT ); Wed, 16 May 2007 18:48:33 -0400 Message-ID: <379355695.11913@ustc.edu.cn> X-EYOUMAIL-SMTPAUTH: wfg@mail.ustc.edu.cn Message-Id: <20070516224818.384876951@mail.ustc.edu.cn> References: <20070516224752.500812933@mail.ustc.edu.cn> User-Agent: quilt/0.45-1 Date: Thu, 17 May 2007 06:47:54 +0800 From: Fengguang Wu To: Andrew Morton Cc: linux-kernel@vger.kernel.org Cc: Andi Kleen Cc: Jens Axboe Cc: Oleg Nesterov Cc: Steven Pratt Cc: Ram Pai Subject: [PATCH 2/9] readahead: add look-ahead support to __do_page_cache_readahead() Content-Disposition: inline; filename=readahead-add-look-ahead-support-to-__do_page_cache_readahead.patch Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3242 Lines: 92 Add look-ahead support to __do_page_cache_readahead(). It works by - mark the Nth backwards page with PG_readahead, (which instructs the page's first reader to invoke readahead) - and only do the marking for newly allocated pages. (to prevent blindly doing readahead on already cached pages) Look-ahead is a technique to achieve I/O pipelining: While the application is working through a chunk of cached pages, the kernel reads-ahead the next chunk of pages _before_ time of need. It effectively hides low level I/O latencies to high level applications. Signed-off-by: Fengguang Wu --- mm/readahead.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) --- linux-2.6.22-rc1-mm1.orig/mm/readahead.c +++ linux-2.6.22-rc1-mm1/mm/readahead.c @@ -265,7 +265,8 @@ out: */ static int __do_page_cache_readahead(struct address_space *mapping, struct file *filp, - pgoff_t offset, unsigned long nr_to_read) + pgoff_t offset, unsigned long nr_to_read, + unsigned long lookahead_size) { struct inode *inode = mapping->host; struct page *page; @@ -278,7 +279,7 @@ __do_page_cache_readahead(struct address if (isize == 0) goto out; - end_index = ((isize - 1) >> PAGE_CACHE_SHIFT); + end_index = ((isize - 1) >> PAGE_CACHE_SHIFT); /* * Preallocate as many pages as we will need. @@ -301,6 +302,8 @@ __do_page_cache_readahead(struct address break; page->index = page_offset; list_add(&page->lru, &page_pool); + if (page_idx == nr_to_read - lookahead_size) + SetPageReadahead(page); ret++; } read_unlock_irq(&mapping->tree_lock); @@ -337,7 +340,7 @@ int force_page_cache_readahead(struct ad if (this_chunk > nr_to_read) this_chunk = nr_to_read; err = __do_page_cache_readahead(mapping, filp, - offset, this_chunk); + offset, this_chunk, 0); if (err < 0) { ret = err; break; @@ -384,7 +387,7 @@ int do_page_cache_readahead(struct addre if (bdi_read_congested(mapping->backing_dev_info)) return -1; - return __do_page_cache_readahead(mapping, filp, offset, nr_to_read); + return __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0); } /* @@ -404,7 +407,7 @@ blockable_page_cache_readahead(struct ad if (!block && bdi_read_congested(mapping->backing_dev_info)) return 0; - actual = __do_page_cache_readahead(mapping, filp, offset, nr_to_read); + actual = __do_page_cache_readahead(mapping, filp, offset, nr_to_read, 0); return check_ra_success(ra, nr_to_read, actual); } @@ -449,7 +452,7 @@ static int make_ahead_window(struct addr * @req_size: hint: total size of the read which the caller is performing in * PAGE_CACHE_SIZE units * - * page_cache_readahead() is the main function. If performs the adaptive + * page_cache_readahead() is the main function. It performs the adaptive * readahead window size management and submits the readahead I/O. * * Note that @filp is purely used for passing on to the ->readpage[s]() -- - 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/