Re: [PATCH] - Improve drain pages performance on large systems
From: David Rientjes <rientjes@google.com>
Date: 2011-02-16 03:01:47
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On Wed, 16 Feb 2011, Minchan Kim wrote:
quoted
Index: linux/mm/page_alloc.c ===================================================================--- linux.orig/mm/page_alloc.c A 2011-02-15 16:28:36.165921713 -0600 +++ linux/mm/page_alloc.c A A A 2011-02-15 16:29:43.085502487 -0600@@ -592,10 +592,24 @@ static void free_pcppages_bulk(struct zoA A A A int batch_free = 0; A A A A int to_free = count; + A A A /* + A A A A * Quick scan of zones. If all are empty, there is nothing to do. + A A A A */ + A A A for (migratetype = 0; migratetype < MIGRATE_PCPTYPES; migratetype++) { + A A A A A A A struct list_head *list; + + A A A A A A A list = &pcp->lists[migratetype]; + A A A A A A A if (!list_empty(list)) + A A A A A A A A A A A break; + A A A } + A A A if (migratetype == MIGRATE_PCPTYPES) + A A A A A A A return; + A A A A spin_lock(&zone->lock); A A A A zone->all_unreclaimable = 0; A A A A zone->pages_scanned = 0; + A A A migratetype = 0; A A A A while (to_free) { A A A A A A A A struct page *page; A A A A A A A A struct list_head *list;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.
I was going to mention the implications for small machines as well, this doesn't look good for callers that know free_pcppages_bulk() will do something.
quoted hunk ↗ jump to hunk
But how about this? This one never affect fast-critical path.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); } }
Right, this is 2ff754fa upstream. I'm wondering if Jack still sees the same problem since 2.6.38-rc3.