From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754954AbcBXBi5 (ORCPT ); Tue, 23 Feb 2016 20:38:57 -0500 Received: from gum.cmpxchg.org ([85.214.110.215]:60044 "EHLO gum.cmpxchg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754408AbcBXBiz (ORCPT ); Tue, 23 Feb 2016 20:38:55 -0500 From: Johannes Weiner To: Andrew Morton , Linus Torvalds Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: [PATCH] mm: readahead: do not cap readahead() and MADV_WILLNEED Date: Tue, 23 Feb 2016 17:38:47 -0800 Message-Id: <1456277927-12044-1-git-send-email-hannes@cmpxchg.org> X-Mailer: git-send-email 2.7.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org All readahead is currently capped to a maximum of the device readahead limit, which defaults to 128k. For heuristics-based readahead this makes perfect sense, too, but unfortunately the limit is also applied to the explicit readahead() or madvise(MADV_WILLNEED) syscalls, and 128k is an awfully low limit, particularly for bigger machines. It's not unreasonable for a user on a 100G machine to say, read this 1G file, and read it now, I'm going to access the whole thing shortly. Since both readahead() and MADV_WILLNEED take an explicit length parameter, it seems weird to truncate that request quietly. Just do what the user asked for and leave the limiting to the heuristics. Signed-off-by: Johannes Weiner --- mm/readahead.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/readahead.c b/mm/readahead.c index 20e58e8..6d182db 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -212,7 +212,6 @@ int force_page_cache_readahead(struct address_space *mapping, struct file *filp, if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages)) return -EINVAL; - nr_to_read = min(nr_to_read, inode_to_bdi(mapping->host)->ra_pages); while (nr_to_read) { int err; @@ -485,6 +484,7 @@ void page_cache_sync_readahead(struct address_space *mapping, /* be dumb */ if (filp && (filp->f_mode & FMODE_RANDOM)) { + req_size = min(req_size, inode_to_bdi(mapping->host)->ra_pages); force_page_cache_readahead(mapping, filp, offset, req_size); return; } -- 2.7.1