Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966598AbWKOH4X (ORCPT ); Wed, 15 Nov 2006 02:56:23 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S966593AbWKOH4F (ORCPT ); Wed, 15 Nov 2006 02:56:05 -0500 Received: from smtp.ustc.edu.cn ([202.38.64.16]:7629 "HELO ustc.edu.cn") by vger.kernel.org with SMTP id S1755473AbWKOHuc (ORCPT ); Wed, 15 Nov 2006 02:50:32 -0500 Message-ID: <363577020.21912@ustc.edu.cn> X-EYOUMAIL-SMTPAUTH: wfg@mail.ustc.edu.cn Message-Id: <20061115075024.180138257@localhost.localdomain> References: <20061115075007.832957580@localhost.localdomain> Date: Wed, 15 Nov 2006 15:50:08 +0800 From: Wu Fengguang To: Andrew Morton Cc: linux-kernel@vger.kernel.org, Wu Fengguang Subject: [PATCH 01/28] readahead: kconfig options Content-Disposition: inline; filename=readahead-kconfig-options.patch Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4945 Lines: 140 This patchset introduces a set of adaptive read-ahead methods. They enable the kernel to better support many important I/O applications. MAIN FEATURES ============= - Adaptive read-ahead buffer management - aggressive, thrashing safe read-ahead size - optimal memory utilisation while achieving good I/O throughput - unnecessary to hand tuning VM_MAX_READAHEAD - support slow/fast readers at the same time - support large number of concurrent readers - aggressive read-ahead on start-of-file - configurable recommended read-ahead size - safeguarded by dynamic estimated thrashing threshold - good for lots-of-small-files case - shrinkable look-ahead size - cut down up to 40% memory consumption on overloaded situation - Detecting any form of (semi-)sequencial scan - parallel / interleaved sequential scans on one fd - sequential reads across file open/close lifetime - mixed sequential / random accesses - sparse / skimming sequential read - Support more access patterns - backward prefetching - Better special case handling - nfs daemon support: the raparams cache is no longer required - laptop mode support: defer look-ahead on drive spinned down - loopback file support: avoid double look-ahead DESIGN STRATEGIES ================= - Dual methods design - stateful method: the fast and default one - stateless method: the robust and failsafe one - if anything abnormal happens, the stateful method bails out, the stateless method queries the page cache and possibly restart the read-ahead process - Robust feedback design - sense and handle important states so that the logic wont run away - detect danger of thrashing and prevent it in advance - extensive accounting and debugging traces This patch: Add kconfig options to enable/disable: - adaptive read-ahead logic - adaptive read-ahead debug traces and events accounting The read-ahead introduction text is cited from the well written LWN article "Adaptive file readahead" :) Signed-off-by: Wu Fengguang Signed-off-by: Andrew Morton --- linux-2.6.19-rc4-mm1.orig/mm/Kconfig +++ linux-2.6.19-rc4-mm1/mm/Kconfig @@ -163,3 +163,60 @@ config ZONE_DMA_FLAG default "0" if !ZONE_DMA default "1" +# +# Adaptive file readahead +# +config ADAPTIVE_READAHEAD + bool "Adaptive file readahead (EXPERIMENTAL)" + default n + depends on EXPERIMENTAL + help + Readahead is a technique employed by the kernel in an attempt + to improve file reading performance. If the kernel has reason + to believe that a particular file is being read sequentially, + it will attempt to read blocks from the file into memory before + the application requests them. When readahead works, it speeds + up the system's throughput, since the reading application does + not have to wait for its requests. When readahead fails, instead, + it generates useless I/O and occupies memory pages which are + needed for some other purpose. + + The kernel already has a stock readahead logic that is well + understood and well tuned. This option enables a more complex and + feature rich one. It tries to be smart and memory efficient. + However, due to the great diversity of real world applications, it + might not fit everyone. + + Please refer to Documentation/sysctl/vm.txt for tunable parameters. + + It is known to work well for many desktops, file servers and + postgresql databases. Say Y to try it out for yourself. + +config DEBUG_READAHEAD + bool "Readahead debug and accounting" + default n + depends on ADAPTIVE_READAHEAD + select DEBUG_FS + help + This option injects extra code to dump detailed debug traces and do + readahead events accounting. + + To actually get the data: + + mkdir /debug + mount -t debug none /debug + + After that you can do the following: + + echo > /debug/readahead/events # reset the counters + cat /debug/readahead/events # check the counters + + echo 1 > /debug/readahead/debug_level # start events accounting + echo 0 > /debug/readahead/debug_level # pause events accounting + + echo 2 > /debug/readahead/debug_level # show printk traces + echo 3 > /debug/readahead/debug_level # show printk traces(verbose) + echo 1 > /debug/readahead/debug_level # stop filling my kern.log + + Say N for production servers. + --- linux-2.6.19-rc4-mm1.orig/mm/readahead.c +++ linux-2.6.19-rc4-mm1/mm/readahead.c @@ -5,6 +5,8 @@ * * 09Apr2002 akpm@zip.com.au * Initial version. + * 26May2006 Fengguang Wu + * Adaptive read-ahead framework. */ #include -- - 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/