Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757217Ab0BUDZj (ORCPT ); Sat, 20 Feb 2010 22:25:39 -0500 Received: from mga14.intel.com ([143.182.124.37]:26655 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757181Ab0BUDZi (ORCPT ); Sat, 20 Feb 2010 22:25:38 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.49,511,1262592000"; d="scan'208";a="246272378" Date: Sun, 21 Feb 2010 11:25:33 +0800 From: Wu Fengguang To: Andy Isaacson Cc: Chris Frost , Andi Kleen , Andrew Morton , Heiko Carstens , Alexander Viro , Benny Halevy , "Andrew@firstfloor.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Steve VanDeBogart , "linux-fsdevel@vger.kernel.org" , Matt Mackall , Peter Zijlstra , Ingo Molnar Subject: Re: [PATCH] fs: add fincore(2) (mincore(2) for file descriptors) Message-ID: <20100221032533.GB14056@localhost> References: <20100216181312.GA9700@frostnet.net> <20100221030238.GA26511@hexapodia.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100221030238.GA26511@hexapodia.org> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1909 Lines: 47 Andy and Chris, On Sun, Feb 21, 2010 at 11:02:38AM +0800, Andy Isaacson wrote: > On Tue, Feb 16, 2010 at 10:13:12AM -0800, Chris Frost wrote: > > Add the fincore() system call. fincore() is mincore() for file descriptors. > > > > The functionality of fincore() can be emulated with an mmap(), mincore(), > > and munmap(), but this emulation requires more system calls and requires > > page table modifications. fincore() can provide a significant performance > > improvement for non-sequential in-core queries. > > In addition to being expensive, mmap/mincore/munmap perturb the VM's > eviction algorithm -- a page is less likely to be evicted if it's > mmapped when being considered for eviction. > > I frequently see this happen when using mincore(1) from > http://bitbucket.org/radii/mincore/ -- "watch mincore -v *.big" while > *.big are being sequentially read results in a significant number of > pages remaining in-core, whereas if I only run mincore after the > sequential read is complete, the large files will be nearly-completely > out of core (except for the tail of the last file, of course). > > It's very interesting to watch > % watch --interval=.5 mincore -v * > > while an IO-intensive process is happening, such as mke2fs on a > filesystem image. > > So, I support the addition of fincore(2) and would use it if it were > merged. I'd like to advocate the "pagecache object collections", a ftrace based alternative: http://lkml.org/lkml/2010/2/9/156 Which will provide much more information than fincore(). I'd really appreciate it if you can join and use the general "pagecache object collections" facility. 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/