Re: [PATCH] - Improve drain pages performance on large systems
From: Jack Steiner <hidden>
Date: 2011-02-16 15:44:16
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On Wed, Feb 16, 2011 at 09:00:59AM +0900, Minchan Kim wrote:
On Wed, Feb 16, 2011 at 7:38 AM, Jack Steiner [off-list ref] wrote:quoted
Heavy swapping within a cpuset causes frequent calls to drain_all_pages(). This sends IPIs to all cpus to free PCP pages. In most cases, there are no pages to be freed on cpus outside of the swapping cpuset. Add checks to minimize locking and updates to potentially hot cachelines. Before acquiring locks, do a quick check to see if any pages are in the PCP queues. Exit if none. On a 128 node SGI UV system, this reduced the IPI overhead to cpus outside of the swapping cpuset by 38% and improved time to run a pass of the swaping test from 98 sec to 51 sec. These times are obviously test & configuration dependent but the improvements are significant. Signed-off-by: Jack Steiner <redacted> --- mm/page_alloc.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) Index: linux/mm/page_alloc.c ===================================================================--- linux.orig/mm/page_alloc.c 2011-02-15 16:28:36.165921713 -0600 +++ linux/mm/page_alloc.c 2011-02-15 16:29:43.085502487 -0600@@ -592,10 +592,24 @@ static void free_pcppages_bulk(struct zo int batch_free = 0; int to_free = count; + /* + * Quick scan of zones. If all are empty, there is nothing to do. + */ + for (migratetype = 0; migratetype < MIGRATE_PCPTYPES; migratetype++) { + struct list_head *list; + + list = &pcp->lists[migratetype]; + if (!list_empty(list)) + break; + } + if (migratetype == MIGRATE_PCPTYPES) + return; + spin_lock(&zone->lock); zone->all_unreclaimable = 0; zone->pages_scanned = 0; + migratetype = 0; while (to_free) { struct page *page; struct list_head *list; --To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>It does make sense to me. Although new code looks to be rather costly in small box, anyway we use the same logic in while loop so cache would be hot. so cost would be little. But how about this? This one never affect fast-critical path.
Yes. Much cleaner. And even better, as David points out it is already in the tree. I did my original testing on a 2.6.32 distro kernel & missed the fact that this was recently fixed upstream. My patch from yesterday can be discarded.
quoted hunk ↗ jump to hunk
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index ff7e158..2dfb61a 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c@@ -1095,8 +1095,10 @@ static void drain_pages(unsigned int cpu) pset = per_cpu_ptr(zone->pageset, cpu); pcp = &pset->pcp; - free_pcppages_bulk(zone, pcp->count, pcp); - pcp->count = 0; + if (pcp->count > 0) { + free_pcppages_bulk(zone, pcp->count, pcp); + pcp->count = 0; + } local_irq_restore(flags); } }-- Kind regards, Minchan Kim
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