Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757713Ab0DGKfd (ORCPT ); Wed, 7 Apr 2010 06:35:33 -0400 Received: from gir.skynet.ie ([193.1.99.77]:57812 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757733Ab0DGKf1 (ORCPT ); Wed, 7 Apr 2010 06:35:27 -0400 Date: Wed, 7 Apr 2010 11:35:07 +0100 From: Mel Gorman To: Andrew Morton Cc: Andrea Arcangeli , Christoph Lameter , Adam Litke , Avi Kivity , David Rientjes , Minchan Kim , KAMEZAWA Hiroyuki , KOSAKI Motohiro , Rik van Riel , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 05/14] Export unusable free space index via /proc/unusable_index Message-ID: <20100407103506.GO17882@csn.ul.ie> References: <1270224168-14775-1-git-send-email-mel@csn.ul.ie> <1270224168-14775-6-git-send-email-mel@csn.ul.ie> <20100406170537.c84f54b7.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20100406170537.c84f54b7.akpm@linux-foundation.org> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7632 Lines: 214 On Tue, Apr 06, 2010 at 05:05:37PM -0700, Andrew Morton wrote: > On Fri, 2 Apr 2010 17:02:39 +0100 > Mel Gorman wrote: > > > Unusable free space index is a measure of external fragmentation that > > takes the allocation size into account. For the most part, the huge page > > size will be the size of interest but not necessarily so it is exported > > on a per-order and per-zone basis via /proc/unusable_index. > > I'd suggest /proc/sys/vm/unusable_index. I don't know how pagetypeinfo > found its way into the top-level dir. > For the same reason buddyinfo did - no one complained. It keeps the fragmentation-related information in the same place but I can move it. > > The index is a value between 0 and 1. It can be expressed as a > > percentage by multiplying by 100 as documented in > > Documentation/filesystems/proc.txt. > > > > ... > > > > +> cat /proc/unusable_index > > +Node 0, zone DMA 0.000 0.000 0.000 0.001 0.005 0.013 0.021 0.037 0.037 0.101 0.230 > > +Node 0, zone Normal 0.000 0.000 0.000 0.001 0.002 0.002 0.005 0.015 0.028 0.028 0.054 > > + > > +The unusable free space index measures how much of the available free > > +memory cannot be used to satisfy an allocation of a given size and is a > > +value between 0 and 1. The higher the value, the more of free memory is > > +unusable and by implication, the worse the external fragmentation is. This > > +can be expressed as a percentage by multiplying by 100. > > That's going to hurt my brain. Why didn't it report usable free blocks? > Lets say you are graphing the index on a given order over time. If there are a large number of frees, there can be a large change in that value but it does nto necessarily tell you how much better or worse the system is overall. > Also, the index is scaled by the actual amount of free memory in the > zones, yes? So to work out how many order-N pages are available you > first need to know how many free pages there are? > It depends on what your question is. As I'm interest in fragmentation, this value gives me information on that. Your question is about how many pages of a given order can be allocated right now and that can be worked out from buddyinfo. > Seems complicated. > > > > > + > > +struct contig_page_info { > > + unsigned long free_pages; > > + unsigned long free_blocks_total; > > + unsigned long free_blocks_suitable; > > +}; > > + > > +/* > > + * Calculate the number of free pages in a zone, how many contiguous > > + * pages are free and how many are large enough to satisfy an allocation of > > + * the target size. Note that this function makes no attempt to estimate > > + * how many suitable free blocks there *might* be if MOVABLE pages were > > + * migrated. Calculating that is possible, but expensive and can be > > + * figured out from userspace > > + */ > > +static void fill_contig_page_info(struct zone *zone, > > + unsigned int suitable_order, > > + struct contig_page_info *info) > > +{ > > + unsigned int order; > > + > > + info->free_pages = 0; > > + info->free_blocks_total = 0; > > + info->free_blocks_suitable = 0; > > + > > + for (order = 0; order < MAX_ORDER; order++) { > > + unsigned long blocks; > > + > > + /* Count number of free blocks */ > > + blocks = zone->free_area[order].nr_free; > > + info->free_blocks_total += blocks; > > + > > + /* Count free base pages */ > > + info->free_pages += blocks << order; > > + > > + /* Count the suitable free blocks */ > > + if (order >= suitable_order) > > + info->free_blocks_suitable += blocks << > > + (order - suitable_order); > > + } > > +} > > + > > +/* > > + * Return an index indicating how much of the available free memory is > > + * unusable for an allocation of the requested size. > > + */ > > +static int unusable_free_index(unsigned int order, > > + struct contig_page_info *info) > > +{ > > + /* No free memory is interpreted as all free memory is unusable */ > > + if (info->free_pages == 0) > > + return 1000; > > + > > + /* > > + * Index should be a value between 0 and 1. Return a value to 3 > > + * decimal places. > > + * > > + * 0 => no fragmentation > > + * 1 => high fragmentation > > + */ > > + return div_u64((info->free_pages - (info->free_blocks_suitable << order)) * 1000ULL, info->free_pages); > > + > > +} > > + > > +static void unusable_show_print(struct seq_file *m, > > + pg_data_t *pgdat, struct zone *zone) > > +{ > > + unsigned int order; > > + int index; > > + struct contig_page_info info; > > + > > + seq_printf(m, "Node %d, zone %8s ", > > + pgdat->node_id, > > + zone->name); > > + for (order = 0; order < MAX_ORDER; ++order) { > > + fill_contig_page_info(zone, order, &info); > > + index = unusable_free_index(order, &info); > > + seq_printf(m, "%d.%03d ", index / 1000, index % 1000); > > + } > > + > > + seq_putc(m, '\n'); > > +} > > + > > +/* > > + * Display unusable free space index > > + * XXX: Could be a lot more efficient, but it's not a critical path > > + */ > > +static int unusable_show(struct seq_file *m, void *arg) > > +{ > > + pg_data_t *pgdat = (pg_data_t *)arg; > > + > > + /* check memoryless node */ > > + if (!node_state(pgdat->node_id, N_HIGH_MEMORY)) > > + return 0; > > + > > + walk_zones_in_node(m, pgdat, unusable_show_print); > > + > > + return 0; > > +} > > + > > static void pagetypeinfo_showfree_print(struct seq_file *m, > > pg_data_t *pgdat, struct zone *zone) > > { > > @@ -603,6 +703,25 @@ static const struct file_operations pagetypeinfo_file_ops = { > > .release = seq_release, > > }; > > > > +static const struct seq_operations unusable_op = { > > + .start = frag_start, > > + .next = frag_next, > > + .stop = frag_stop, > > + .show = unusable_show, > > +}; > > + > > +static int unusable_open(struct inode *inode, struct file *file) > > +{ > > + return seq_open(file, &unusable_op); > > +} > > + > > +static const struct file_operations unusable_file_ops = { > > + .open = unusable_open, > > + .read = seq_read, > > + .llseek = seq_lseek, > > + .release = seq_release, > > +}; > > + > > #ifdef CONFIG_ZONE_DMA > > #define TEXT_FOR_DMA(xx) xx "_dma", > > #else > > @@ -947,6 +1066,7 @@ static int __init setup_vmstat(void) > > #ifdef CONFIG_PROC_FS > > proc_create("buddyinfo", S_IRUGO, NULL, &fragmentation_file_operations); > > proc_create("pagetypeinfo", S_IRUGO, NULL, &pagetypeinfo_file_ops); > > + proc_create("unusable_index", S_IRUGO, NULL, &unusable_file_ops); > > proc_create("vmstat", S_IRUGO, NULL, &proc_vmstat_file_operations); > > proc_create("zoneinfo", S_IRUGO, NULL, &proc_zoneinfo_file_operations); > > #endif > > All this code will be bloat for most people, I suspect. Can we find a > suitable #ifdef wrapper to keep my cellphone happy? > It could. However, this information can also be created from buddyinfo and I have a perl script that can be adapted to duplicate the output of this proc file. As there isn't an in-kernel user of this information, it can also be dropped. Will I roll a patch that moves the proc entry and makes it a CONFIG option or will I just remove the file altogether? If I remove it, I can adapt the perl script and add to the other hugepage-related utilities in libhugetlbfs. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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/