Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756027Ab0AFRuo (ORCPT ); Wed, 6 Jan 2010 12:50:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755992Ab0AFRun (ORCPT ); Wed, 6 Jan 2010 12:50:43 -0500 Received: from gir.skynet.ie ([193.1.99.77]:35827 "EHLO gir.skynet.ie" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755947Ab0AFRum (ORCPT ); Wed, 6 Jan 2010 12:50:42 -0500 Date: Wed, 6 Jan 2010 17:50:32 +0000 From: Mel Gorman To: Andrea Arcangeli Cc: Christoph Lameter , Adam Litke , Avi Kivity , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 4/7] Memory compaction core Message-ID: <20100106175031.GB5426@csn.ul.ie> References: <1262795169-9095-1-git-send-email-mel@csn.ul.ie> <1262795169-9095-5-git-send-email-mel@csn.ul.ie> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <1262795169-9095-5-git-send-email-mel@csn.ul.ie> 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: 17817 Lines: 547 On Wed, Jan 06, 2010 at 04:26:06PM +0000, Mel Gorman wrote: > This patch is the core of a mechanism which compacts memory in a zone by > relocating movable pages towards the end of the zone. > > A single compaction run involves a migration scanner and a free scanner. > Both scanners operate on pageblock-sized areas in the zone. The migration > scanner starts at the bottom of the zone and searches for all movable pages > within each area, isolating them onto a private list called migratelist. > The free scanner starts at the top of the zone and searches for suitable > areas and consumes the free pages within making them available for the > migration scanner. The pages isolated for migration are then migrated to > the newly isolated free pages. > > TODO > o Rethink block selection for migration. When originally developed, > there was a deliberate effort to place MIGRATE_UNMOVABLE pages > to the lower PFNs so the block selection made a lot of sense. > However, that is no longer the case so rethink. > > Signed-off-by: Mel Gorman > --- > include/linux/compaction.h | 8 + > include/linux/mm.h | 1 + > include/linux/swap.h | 5 + > include/linux/vmstat.h | 1 + > mm/Makefile | 1 + > mm/compaction.c | 340 ++++++++++++++++++++++++++++++++++++++++++++ > mm/page_alloc.c | 37 +++++ > mm/vmscan.c | 5 - > mm/vmstat.c | 5 + > 9 files changed, 398 insertions(+), 5 deletions(-) > create mode 100644 include/linux/compaction.h > create mode 100644 mm/compaction.c > > diff --git a/include/linux/compaction.h b/include/linux/compaction.h > new file mode 100644 > index 0000000..6201371 > --- /dev/null > +++ b/include/linux/compaction.h > @@ -0,0 +1,8 @@ > +#ifndef _LINUX_COMPACTION_H > +#define _LINUX_COMPACTION_H > + > +/* Return values for compact_zone() */ > +#define COMPACT_INCOMPLETE 0 > +#define COMPACT_COMPLETE 1 > + > +#endif /* _LINUX_COMPACTION_H */ > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 2265f28..757ab86 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -332,6 +332,7 @@ void put_page(struct page *page); > void put_pages_list(struct list_head *pages); > > void split_page(struct page *page, unsigned int order); > +int split_free_page(struct page *page); > > /* > * Compound pages have a destructor function. Provide a > diff --git a/include/linux/swap.h b/include/linux/swap.h > index a2602a8..7e7181b 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -238,6 +238,11 @@ static inline void lru_cache_add_active_file(struct page *page) > __lru_cache_add(page, LRU_ACTIVE_FILE); > } > > +/* LRU Isolation modes. */ > +#define ISOLATE_INACTIVE 0 /* Isolate inactive pages. */ > +#define ISOLATE_ACTIVE 1 /* Isolate active pages. */ > +#define ISOLATE_BOTH 2 /* Isolate both active and inactive pages. */ > + > /* linux/mm/vmscan.c */ > extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order, > gfp_t gfp_mask, nodemask_t *mask); > diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h > index ee03bba..d7f7236 100644 > --- a/include/linux/vmstat.h > +++ b/include/linux/vmstat.h > @@ -43,6 +43,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, > KSWAPD_LOW_WMARK_HIT_QUICKLY, KSWAPD_HIGH_WMARK_HIT_QUICKLY, > KSWAPD_SKIP_CONGESTION_WAIT, > PAGEOUTRUN, ALLOCSTALL, PGROTATED, > + COMPACTBLOCKS, COMPACTPAGES, COMPACTPAGEFAILED, > #ifdef CONFIG_HUGETLB_PAGE > HTLB_BUDDY_PGALLOC, HTLB_BUDDY_PGALLOC_FAIL, > #endif > diff --git a/mm/Makefile b/mm/Makefile > index 7a68d2a..ccb1f72 100644 > --- a/mm/Makefile > +++ b/mm/Makefile > @@ -33,6 +33,7 @@ obj-$(CONFIG_FAILSLAB) += failslab.o > obj-$(CONFIG_MEMORY_HOTPLUG) += memory_hotplug.o > obj-$(CONFIG_FS_XIP) += filemap_xip.o > obj-$(CONFIG_MIGRATION) += migrate.o > +obj-$(CONFIG_COMPACTION) += compaction.o > obj-$(CONFIG_SMP) += percpu.o > obj-$(CONFIG_QUICKLIST) += quicklist.o > obj-$(CONFIG_CGROUP_MEM_RES_CTLR) += memcontrol.o page_cgroup.o > diff --git a/mm/compaction.c b/mm/compaction.c > new file mode 100644 > index 0000000..d36760a > --- /dev/null > +++ b/mm/compaction.c > @@ -0,0 +1,340 @@ > +/* > + * linux/mm/compaction.c > + * > + * Memory compaction for the reduction of external fragmentation. Note that > + * this heavily depends upon page migration to do all the real heavy > + * lifting > + * > + * Copyright IBM Corp. 2009 Mel Gorman > + */ > +#include > +#include > +#include > +#include > +#include "internal.h" > + > +/* > + * compact_control is used to track pages being migrated and the free pages > + * they are being migrated to during memory compaction. The free_pfn starts > + * at the end of a zone and migrate_pfn begins at the start. Movable pages > + * are moved to the end of a zone during a compaction run and the run > + * completes when free_pfn <= migrate_pfn > + */ > +struct compact_control { > + struct list_head freepages; /* List of free pages to migrate to */ > + struct list_head migratepages; /* List of pages being migrated */ > + unsigned long nr_freepages; /* Number of isolated free pages */ > + unsigned long nr_migratepages; /* Number of pages to migrate */ > + unsigned long free_pfn; /* isolate_freepages search base */ > + unsigned long migrate_pfn; /* isolate_migratepages search base */ > + struct zone *zone; > +}; > + > +static int release_freepages(struct zone *zone, struct list_head *freelist) > +{ > + struct page *page, *next; > + int count = 0; > + > + list_for_each_entry_safe(page, next, freelist, lru) { > + list_del(&page->lru); > + __free_page(page); > + count++; > + } > + > + return count; > +} > + > +/* Isolate free pages onto a private freelist. Must hold zone->lock */ > +static int isolate_freepages_block(struct zone *zone, > + unsigned long blockpfn, > + struct list_head *freelist) > +{ > + unsigned long zone_end_pfn, end_pfn; > + int total_isolated = 0; > + > + /* Get the last PFN we should scan for free pages at */ > + zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages; > + end_pfn = blockpfn + pageblock_nr_pages; > + if (end_pfn > zone_end_pfn) > + end_pfn = zone_end_pfn; > + > + /* Isolate free pages. This assumes the block is valid */ > + for (; blockpfn < end_pfn; blockpfn++) { > + struct page *page; > + int isolated, i; > + > + if (!pfn_valid_within(blockpfn)) > + continue; > + > + page = pfn_to_page(blockpfn); > + if (!PageBuddy(page)) > + continue; > + > + /* Found a free page, break it into order-0 pages */ > + isolated = split_free_page(page); > + total_isolated += isolated; > + for (i = 0; i < isolated; i++) { > + list_add(&page->lru, freelist); > + page++; > + blockpfn += isolated - 1; *sigh* This increment is wrong. It pushs blockpfn forward too fast and takes fewer free pages than it should from that pageblock. > + } > + } > + > + return total_isolated; > +} > + > +/* Returns 1 if the page is within a block suitable for migration to */ > +static int suitable_migration_target(struct page *page) > +{ > + /* If the page is a large free page, then allow migration */ > + if (PageBuddy(page) && page_order(page) >= pageblock_order) > + return 1; > + > + /* If the block is MIGRATE_MOVABLE, allow migration */ > + if (get_pageblock_migratetype(page) == MIGRATE_MOVABLE) > + return 1; > + > + /* Otherwise skip the block */ > + return 0; > +} > + > +/* > + * Based on information in the current compact_control, find blocks > + * suitable for isolating free pages from > + */ > +static void isolate_freepages(struct zone *zone, > + struct compact_control *cc) > +{ > + struct page *page; > + unsigned long high_pfn, low_pfn, pfn; > + int nr_freepages = cc->nr_freepages; > + struct list_head *freelist = &cc->freepages; > + > + pfn = cc->free_pfn; > + low_pfn = cc->migrate_pfn + pageblock_nr_pages; > + high_pfn = low_pfn; > + > + /* > + * Isolate free pages until enough are available to migrate the > + * pages on cc->migratepages. We stop searching if the migrate > + * and free page scanners meet or enough free pages are isolated. > + */ > + spin_lock_irq(&zone->lock); > + for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages; > + pfn -= pageblock_nr_pages) { > + int isolated; > + > + if (!pfn_valid(pfn)) > + continue; > + > + /* Check for overlapping nodes/zones */ > + page = pfn_to_page(pfn); > + if (page_zone(page) != zone) > + continue; > + > + /* Check the block is suitable for migration */ > + if (!suitable_migration_target(page)) > + continue; > + > + /* Found a block suitable for isolating free pages from */ > + isolated = isolate_freepages_block(zone, pfn, freelist); > + nr_freepages += isolated; > + > + /* > + * Record the highest PFN we isolated pages from. When next > + * looking for free pages, the search will restart here as > + * page migration may have returned some pages to the allocator > + */ > + if (isolated) > + high_pfn = max(high_pfn, pfn); > + } > + spin_unlock_irq(&zone->lock); > + > + cc->free_pfn = high_pfn; > + cc->nr_freepages = nr_freepages; > +} > + > +/* > + * Isolate all pages that can be migrated from the block pointed to by > + * the migrate scanner within compact_control. > + */ > +static unsigned long isolate_migratepages(struct zone *zone, > + struct compact_control *cc) > +{ > + unsigned long low_pfn, end_pfn; > + struct list_head *migratelist; > + enum lru_list lru_src; > + > + low_pfn = ALIGN(cc->migrate_pfn, pageblock_nr_pages); > + migratelist = &cc->migratepages; > + > + /* Do not scan outside zone boundaries */ > + if (low_pfn < zone->zone_start_pfn) > + low_pfn = zone->zone_start_pfn; > + > + /* Setup to scan one block but not past where we are migrating to */ > + end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages); > + cc->migrate_pfn = end_pfn; > + VM_BUG_ON(end_pfn > cc->free_pfn); > + > + if (!pfn_valid(low_pfn)) > + return 0; > + > + migrate_prep(); > + > + /* Time to isolate some pages for migration */ > + spin_lock_irq(&zone->lru_lock); > + for (; low_pfn < end_pfn; low_pfn++) { > + struct page *page; > + if (!pfn_valid_within(low_pfn)) > + continue; > + > + /* Get the page and skip if free */ > + page = pfn_to_page(low_pfn); > + if (PageBuddy(page)) { > + low_pfn += (1 << page_order(page)) - 1; > + continue; > + } > + > + if (!PageLRU(page) || PageUnevictable(page)) > + continue; > + > + /* Try isolate the page */ > + lru_src = page_lru(page); > + switch (__isolate_lru_page(page, ISOLATE_BOTH, 0)) { > + case 0: > + list_move(&page->lru, migratelist); > + mem_cgroup_del_lru(page); > + cc->nr_migratepages++; > + break; > + > + case -EBUSY: > + /* > + * else it is being freed elsewhere. The > + * problem is that we are not really sure where > + * it came from in the first place > + * XXX: Verify the putback logic is ok. This was > + * all written before LRU lists were split > + */ > + list_move(&page->lru, &zone->lru[lru_src].list); > + mem_cgroup_rotate_lru_list(page, page_lru(page)); > + continue; > + > + default: > + BUG(); > + } > + } > + spin_unlock_irq(&zone->lru_lock); > + > + return cc->nr_migratepages; > +} > + > +/* > + * This is a migrate-callback that "allocates" freepages by taking pages > + * from the isolated freelists in the block we are migrating to. > + */ > +static struct page *compaction_alloc(struct page *migratepage, > + unsigned long data, > + int **result) > +{ > + struct compact_control *cc = (struct compact_control *)data; > + struct page *freepage; > + > + VM_BUG_ON(cc == NULL); > + > + /* Isolate free pages if necessary */ > + if (list_empty(&cc->freepages)) { > + isolate_freepages(cc->zone, cc); > + > + if (list_empty(&cc->freepages)) > + return NULL; > + } > + > + freepage = list_entry(cc->freepages.next, struct page, lru); > + list_del(&freepage->lru); > + cc->nr_freepages--; > + > + return freepage; > +} > + > +/* > + * We cannot control nr_migratepages and nr_freepages fully when migration is > + * running as migrate_pages() has no knowledge of compact_control. When > + * migration is complete, we count the number of pages on the lists by hand. > + */ > +static void update_nr_listpages(struct compact_control *cc) > +{ > + int nr_migratepages = 0; > + int nr_freepages = 0; > + struct page *page; > + list_for_each_entry(page, &cc->migratepages, lru) > + nr_migratepages++; > + list_for_each_entry(page, &cc->freepages, lru) > + nr_freepages++; > + > + cc->nr_migratepages = nr_migratepages; > + cc->nr_freepages = nr_freepages; > +} > + > +static inline int compact_finished(struct zone *zone, > + struct compact_control *cc) > +{ > + /* Compaction run completes if the migrate and free scanner meet */ > + if (cc->free_pfn <= cc->migrate_pfn) > + return COMPACT_COMPLETE; > + > + return COMPACT_INCOMPLETE; > +} > + > +static int compact_zone(struct zone *zone, struct compact_control *cc) > +{ > + int ret = COMPACT_INCOMPLETE; > + > + /* > + * Setup to move all movable pages to the end of the zone > + * XXX: This could be improved upon. In the event compaction > + * is being successful quickly but called often, there > + * is a likelihood of scanning the same blocks as sources > + * and targets frequently. Might be worth caching the > + * last migrate_pfn to reduce scan times. > + */ > + cc->migrate_pfn = zone->zone_start_pfn; > + cc->free_pfn = cc->migrate_pfn + zone->spanned_pages; > + cc->free_pfn &= ~(pageblock_nr_pages-1); > + > + for (; ret == COMPACT_INCOMPLETE; ret = compact_finished(zone, cc)) { > + unsigned long nr_migrate, nr_remaining; > + if (!isolate_migratepages(zone, cc)) > + continue; > + > + nr_migrate = cc->nr_migratepages; > + migrate_pages(&cc->migratepages, compaction_alloc, > + (unsigned long)cc, 0); > + update_nr_listpages(cc); > + nr_remaining = cc->nr_migratepages; > + > + count_vm_event(COMPACTBLOCKS); > + count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining); > + if (nr_remaining) > + count_vm_events(COMPACTPAGEFAILED, nr_remaining); > + } > + > + /* Release free pages and check accounting */ > + cc->nr_freepages -= release_freepages(zone, &cc->freepages); > + VM_BUG_ON(cc->nr_freepages != 0); > + > + /* > + * Release LRU pages not migrated > + * XXX: Page migration at this point tries fairly hard to move > + * pages as it is but if migration fails, pages are left > + * on cc->migratepages for more passes. This might cause > + * multiple useless failures. Watch compact_pagemigrate_failed > + * in /proc/vmstat. If it grows a lot, then putback should > + * happen after each failed migration > + */ > + if (!list_empty(&cc->migratepages)) > + putback_lru_pages(&cc->migratepages); > + > + return ret; > +} > + > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 4e9f5cc..462431a 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1167,6 +1167,43 @@ void split_page(struct page *page, unsigned int order) > set_page_refcounted(page + i); > } > > +/* Similar to split_page except the page is already free */ > +int split_free_page(struct page *page) > +{ > + unsigned int order; > + unsigned long watermark; > + struct zone *zone; > + > + BUG_ON(!PageBuddy(page)); > + > + zone = page_zone(page); > + order = page_order(page); > + > + /* Obey watermarks or the system could deadlock */ > + watermark = low_wmark_pages(zone) + (1 << order); > + if (!zone_watermark_ok(zone, 0, watermark, 0, 0)) > + return 0; > + > + /* Remove page from free list */ > + list_del(&page->lru); > + zone->free_area[order].nr_free--; > + rmv_page_order(page); > + __mod_zone_page_state(zone, NR_FREE_PAGES, -(1UL << order)); > + > + /* Split into individual pages */ > + set_page_refcounted(page); > + split_page(page, order); > + > + /* Set the migratetype on the assumption it's for migration */ > + if (order >= pageblock_order - 1) { > + struct page *endpage = page + (1 << order) - 1; > + for (; page < endpage; page += pageblock_nr_pages) > + set_pageblock_migratetype(page, MIGRATE_MOVABLE); > + } > + > + return 1 << order; > +} > + > /* > * Really, prep_compound_page() should be called from __rmqueue_bulk(). But > * we cheat by calling it from here, in the order > 0 path. Saves a branch > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 885207a..2ad8603 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -803,11 +803,6 @@ keep: > return nr_reclaimed; > } > > -/* LRU Isolation modes. */ > -#define ISOLATE_INACTIVE 0 /* Isolate inactive pages. */ > -#define ISOLATE_ACTIVE 1 /* Isolate active pages. */ > -#define ISOLATE_BOTH 2 /* Isolate both active and inactive pages. */ > - > /* > * Attempt to remove the specified page from its LRU. Only take this page > * if it is of the appropriate PageActive status. Pages which are being > diff --git a/mm/vmstat.c b/mm/vmstat.c > index 560ee08..41585bf 100644 > --- a/mm/vmstat.c > +++ b/mm/vmstat.c > @@ -852,6 +852,11 @@ static const char * const vmstat_text[] = { > "allocstall", > > "pgrotated", > + > + "compact_blocks_moved", > + "compact_pages_moved", > + "compact_pagemigrate_failed", > + > #ifdef CONFIG_HUGETLB_PAGE > "htlb_buddy_alloc_success", > "htlb_buddy_alloc_fail", > -- > 1.6.5 > -- 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/