From patchwork Thu Sep 20 14:04:31 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mel Gorman X-Patchwork-Id: 185412 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 2A7C42C0084 for ; Fri, 21 Sep 2012 00:46:08 +1000 (EST) Received: from localhost ([::1]:38278 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TEhNg-0001BQ-0T for incoming@patchwork.ozlabs.org; Thu, 20 Sep 2012 10:05:28 -0400 Received: from eggs.gnu.org ([208.118.235.92]:44139) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TEhN2-00083a-O7 for qemu-devel@nongnu.org; Thu, 20 Sep 2012 10:04:54 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TEhMu-000862-Lr for qemu-devel@nongnu.org; Thu, 20 Sep 2012 10:04:48 -0400 Received: from cantor2.suse.de ([195.135.220.15]:37109 helo=mx2.suse.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TEhMu-00085c-8t for qemu-devel@nongnu.org; Thu, 20 Sep 2012 10:04:40 -0400 Received: from relay1.suse.de (unknown [195.135.220.254]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mx2.suse.de (Postfix) with ESMTP id C49D1A3991; Thu, 20 Sep 2012 16:04:39 +0200 (CEST) From: Mel Gorman To: Richard Davies , Shaohua Li Date: Thu, 20 Sep 2012 15:04:31 +0100 Message-Id: <1348149875-29678-3-git-send-email-mgorman@suse.de> X-Mailer: git-send-email 1.7.9.2 In-Reply-To: <1348149875-29678-1-git-send-email-mgorman@suse.de> References: <1348149875-29678-1-git-send-email-mgorman@suse.de> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.4-2.6 X-Received-From: 195.135.220.15 Cc: KVM , LKML , QEMU-devel , Linux-MM , Avi Kivity , Mel Gorman Subject: [Qemu-devel] [PATCH 2/6] mm: compaction: Acquire the zone->lru_lock as late as possible X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Compactions migrate scanner acquires the zone->lru_lock when scanning a range of pages looking for LRU pages to acquire. It does this even if there are no LRU pages in the range. If multiple processes are compacting then this can cause severe locking contention. To make matters worse commit b2eef8c0 (mm: compaction: minimise the time IRQs are disabled while isolating pages for migration) releases the lru_lock every SWAP_CLUSTER_MAX pages that are scanned. This patch makes two changes to how the migrate scanner acquires the LRU lock. First, it only releases the LRU lock every SWAP_CLUSTER_MAX pages if the lock is contended. This reduces the number of times it unnecessarily disables and re-enables IRQs. The second is that it defers acquiring the LRU lock for as long as possible. If there are no LRU pages or the only LRU pages are transhuge then the LRU lock will not be acquired at all which reduces contention on zone->lru_lock. Signed-off-by: Mel Gorman Acked-by: Rik van Riel --- mm/compaction.c | 63 +++++++++++++++++++++++++++++++++++++------------------ 1 file changed, 43 insertions(+), 20 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index a8de20d..6450c3e 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -50,6 +50,11 @@ static inline bool migrate_async_suitable(int migratetype) return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE; } +static inline bool should_release_lock(spinlock_t *lock) +{ + return need_resched() || spin_is_contended(lock); +} + /* * Compaction requires the taking of some coarse locks that are potentially * very heavily contended. Check if the process needs to be scheduled or @@ -62,7 +67,7 @@ static inline bool migrate_async_suitable(int migratetype) static bool compact_checklock_irqsave(spinlock_t *lock, unsigned long *flags, bool locked, struct compact_control *cc) { - if (need_resched() || spin_is_contended(lock)) { + if (should_release_lock(lock)) { if (locked) { spin_unlock_irqrestore(lock, *flags); locked = false; @@ -275,7 +280,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc, isolate_mode_t mode = 0; struct lruvec *lruvec; unsigned long flags; - bool locked; + bool locked = false; /* * Ensure that there are not too many pages isolated from the LRU @@ -295,23 +300,17 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc, /* Time to isolate some pages for migration */ cond_resched(); - spin_lock_irqsave(&zone->lru_lock, flags); - locked = true; for (; low_pfn < end_pfn; low_pfn++) { struct page *page; /* give a chance to irqs before checking need_resched() */ - if (!((low_pfn+1) % SWAP_CLUSTER_MAX)) { - spin_unlock_irqrestore(&zone->lru_lock, flags); - locked = false; + if (locked && !((low_pfn+1) % SWAP_CLUSTER_MAX)) { + if (should_release_lock(&zone->lru_lock)) { + spin_unlock_irqrestore(&zone->lru_lock, flags); + locked = false; + } } - /* Check if it is ok to still hold the lock */ - locked = compact_checklock_irqsave(&zone->lru_lock, &flags, - locked, cc); - if (!locked) - break; - /* * migrate_pfn does not necessarily start aligned to a * pageblock. Ensure that pfn_valid is called when moving @@ -351,21 +350,38 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc, pageblock_nr = low_pfn >> pageblock_order; if (!cc->sync && last_pageblock_nr != pageblock_nr && !migrate_async_suitable(get_pageblock_migratetype(page))) { - low_pfn += pageblock_nr_pages; - low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1; - last_pageblock_nr = pageblock_nr; - continue; + goto next_pageblock; } + /* Check may be lockless but that's ok as we recheck later */ if (!PageLRU(page)) continue; /* - * PageLRU is set, and lru_lock excludes isolation, - * splitting and collapsing (collapsing has already - * happened if PageLRU is set). + * PageLRU is set. lru_lock normally excludes isolation + * splitting and collapsing (collapsing has already happened + * if PageLRU is set) but the lock is not necessarily taken + * here and it is wasteful to take it just to check transhuge. + * Check transhuge without lock and skip if it's either a + * transhuge or hugetlbfs page. */ if (PageTransHuge(page)) { + if (!locked) + goto next_pageblock; + low_pfn += (1 << compound_order(page)) - 1; + continue; + } + + /* Check if it is ok to still hold the lock */ + locked = compact_checklock_irqsave(&zone->lru_lock, &flags, + locked, cc); + if (!locked) + break; + + /* Recheck PageLRU and PageTransHuge under lock */ + if (!PageLRU(page)) + continue; + if (PageTransHuge(page)) { low_pfn += (1 << compound_order(page)) - 1; continue; } @@ -392,6 +408,13 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc, ++low_pfn; break; } + + continue; + +next_pageblock: + low_pfn += pageblock_nr_pages; + low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1; + last_pageblock_nr = pageblock_nr; } acct_isolated(zone, locked, cc);