Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932237AbVLPMpx (ORCPT ); Fri, 16 Dec 2005 07:45:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932240AbVLPMpw (ORCPT ); Fri, 16 Dec 2005 07:45:52 -0500 Received: from ns.ustc.edu.cn ([202.38.64.1]:33933 "EHLO mx1.ustc.edu.cn") by vger.kernel.org with ESMTP id S932252AbVLPMpi (ORCPT ); Fri, 16 Dec 2005 07:45:38 -0500 Message-Id: <20051216130859.559147000@localhost.localdomain> References: <20051216130738.300284000@localhost.localdomain> Date: Fri, 16 Dec 2005 21:07:42 +0800 From: Wu Fengguang To: linux-kernel@vger.kernel.org Cc: Andrew Morton , Wu Fengguang Subject: [PATCH 04/12] readahead: parameters Content-Disposition: inline; filename=readahead-parameters.patch Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6110 Lines: 189 - new sysctl entries in /proc/sys/vm: - readahead_ratio = 1 - readahead_hit_rate = 2 - dynamic minimal/initial read-ahead size. For now, different ranges of readahead_ratio select different read-ahead code path: condition action =========================================================== readahead_ratio == 0 disable read-ahead readahead_ratio < 9 select old read-ahead logic readahead_ratio >= 9 select new read-ahead logic Signed-off-by: Wu Fengguang --- Documentation/sysctl/vm.txt | 38 ++++++++++++++++++++++++++++++++++++++ include/linux/sysctl.h | 2 ++ kernel/sysctl.c | 23 +++++++++++++++++++++++ mm/readahead.c | 35 +++++++++++++++++++++++++++++++++++ 4 files changed, 98 insertions(+) --- linux.orig/Documentation/sysctl/vm.txt +++ linux/Documentation/sysctl/vm.txt @@ -28,6 +28,8 @@ Currently, these files are in /proc/sys/ - block_dump - drop-caches - swap_prefetch +- readahead_ratio +- readahead_hit_rate ============================================================== @@ -132,3 +134,39 @@ laptop_mode is enabled and then it is te disables prefetching entirely. The default value is dependant on ramsize. + +============================================================== + +readahead_ratio + +This limits read-ahead size to percent of the thrashing-threshold. +The thrashing-threshold is dynamicly estimated according to the +_history_ read speed and system load, and used to limit the +_future_ read-ahead request size. + +Set it to a low value if you have not enough memory to counteract +the I/O load fluctuations. But if there's plenty of memory, set it +to a larger value might help speedup reads. + +readahead_ratio also selects the read-ahead logic: +0: disable read-ahead totally +1-9: select the well tested old read-ahead logic +10-inf: select the new adaptive read-ahead logic + +The default value is 1. +For the new adaptive read-ahead, reasonable values would be 50-100. + +============================================================== + +readahead_hit_rate + +This is the max allowed value of (read-ahead-pages : accessed-pages). +Useful only when (readahead_ratio >= 10). If the previous read-ahead +request has bad hit rate, kernel will be very conservative to issue +the next read-ahead. + +A large value helps speedup some sparse access patterns, at the cost +of more memory consumption. It is recommended to keep the value below +(max-readahead-pages / 8). + +The default value is 2. --- linux.orig/include/linux/sysctl.h +++ linux/include/linux/sysctl.h @@ -184,6 +184,8 @@ enum VM_DROP_PAGECACHE=29, /* int: nuke lots of pagecache */ VM_PERCPU_PAGELIST_FRACTION=30,/* int: fraction of pages in each percpu_pagelist */ VM_SWAP_PREFETCH=31, /* int: amount to swap prefetch */ + VM_READAHEAD_RATIO=32, /* percent of read-ahead size to thrashing-threshold */ + VM_READAHEAD_HIT_RATE=33, /* one accessed page legitimizes so many read-ahead pages */ }; /* CTL_NET names: */ --- linux.orig/kernel/sysctl.c +++ linux/kernel/sysctl.c @@ -70,6 +70,8 @@ extern int printk_ratelimit_burst; extern int pid_max_min, pid_max_max; extern int sysctl_drop_caches; extern int percpu_pagelist_fraction; +extern int readahead_ratio; +extern int readahead_hit_rate; #if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86) int unknown_nmi_panic; @@ -671,6 +673,7 @@ static ctl_table kern_table[] = { /* Constants for minimum and maximum testing in vm_table. We use these as one-element integer vectors. */ static int zero; +static int one = 1; static int one_hundred = 100; @@ -889,6 +892,26 @@ static ctl_table vm_table[] = { }, #endif #endif + { + .ctl_name = VM_READAHEAD_RATIO, + .procname = "readahead_ratio", + .data = &readahead_ratio, + .maxlen = sizeof(readahead_ratio), + .mode = 0644, + .proc_handler = &proc_dointvec, + .strategy = &sysctl_intvec, + .extra1 = &zero, + }, + { + .ctl_name = VM_READAHEAD_HIT_RATE, + .procname = "readahead_hit_rate", + .data = &readahead_hit_rate, + .maxlen = sizeof(readahead_hit_rate), + .mode = 0644, + .proc_handler = &proc_dointvec, + .strategy = &sysctl_intvec, + .extra1 = &one, + }, { .ctl_name = 0 } }; --- linux.orig/mm/readahead.c +++ linux/mm/readahead.c @@ -20,6 +20,20 @@ #define MAX_RA_PAGES KB(VM_MAX_READAHEAD) #define MIN_RA_PAGES KB(VM_MIN_READAHEAD) +/* In laptop mode, poll delayed look-ahead on every ## pages read. */ +#define LAPTOP_POLL_INTERVAL 16 + +/* Set look-ahead size to 1/# of the thrashing-threshold. */ +#define LOOKAHEAD_RATIO 8 + +/* Set read-ahead size to ##% of the thrashing-threshold. */ +int readahead_ratio = 1; +EXPORT_SYMBOL(readahead_ratio); + +/* Readahead as long as cache hit ratio keeps above 1/##. */ +int readahead_hit_rate = 2; +EXPORT_SYMBOL(readahead_hit_rate); + /* Detailed classification of read-ahead behaviors. */ #define RA_CLASS_SHIFT 4 #define RA_CLASS_MASK ((1 << RA_CLASS_SHIFT) - 1) @@ -794,6 +808,27 @@ out: } /* + * ra_size is mainly determined by: + * 1. sequential-start: min(MIN_RA_PAGES + (pages>>14), KB(128)) + * 2. sequential-max: min(ra->ra_pages, 0xFFFF) + * 3. sequential: (thrashing-threshold) * readahead_ratio / 100 + * + * Table of concrete numbers for 4KB page size: + * (inactive + free) (in MB): 4 8 16 32 64 128 256 512 1024 + * initial ra_size (in KB): 16 16 16 16 20 24 32 48 64 + */ +static inline void get_readahead_bounds(struct file_ra_state *ra, + unsigned long *ra_min, + unsigned long *ra_max) +{ + unsigned long pages; + + pages = node_free_and_cold_pages(); + *ra_max = min(min(pages/2, 0xFFFFUL), ra->ra_pages); + *ra_min = min(min(MIN_RA_PAGES + (pages>>14), KB(128)), *ra_max/2); +} + +/* * This is the entry point of the adaptive read-ahead logic. * * It is only called on two conditions: -- - 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/