Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751649Ab2JYE3P (ORCPT ); Thu, 25 Oct 2012 00:29:15 -0400 Received: from mga01.intel.com ([192.55.52.88]:22987 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750712Ab2JYE3O (ORCPT ); Thu, 25 Oct 2012 00:29:14 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.80,643,1344236400"; d="scan'208";a="239951972" Date: Thu, 25 Oct 2012 10:58:26 +0800 From: Fengguang Wu To: Ni zhan Chen Cc: YingHang Zhu , Dave Chinner , akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] mm: readahead: remove redundant ra_pages in file_ra_state Message-ID: <20121025025826.GB23462@localhost> References: <1350996411-5425-1-git-send-email-casualfisher@gmail.com> <20121023224706.GR4291@dastard> <20121024201921.GX4291@dastard> <20121025015014.GC29378@dastard> <50889FF1.9030107@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50889FF1.9030107@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1600 Lines: 38 Hi Chen, > But how can bdi related ra_pages reflect different files' readahead > window? Maybe these different files are sequential read, random read > and so on. It's simple: sequential reads will get ra_pages readahead size while random reads will not get readahead at all. Talking about the below chunk, it might hurt someone that explicitly takes advantage of the behavior, however the ra_pages*2 seems more like a hack than general solution to me: if the user will need POSIX_FADV_SEQUENTIAL to double the max readahead window size for improving IO performance, then why not just increase bdi->ra_pages and benefit all reads? One may argue that it offers some differential behavior to specific applications, however it may also present as a counter-optimization: if the root already tuned bdi->ra_pages to the optimal size, the doubled readahead size will only cost more memory and perhaps IO latency. --- a/mm/fadvise.c +++ b/mm/fadvise.c @@ -87,7 +86,6 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice) spin_unlock(&file->f_lock); break; case POSIX_FADV_SEQUENTIAL: - file->f_ra.ra_pages = bdi->ra_pages * 2; spin_lock(&file->f_lock); file->f_mode &= ~FMODE_RANDOM; spin_unlock(&file->f_lock); Thanks, Fengguang -- 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/