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authorMel Gorman <mgorman@techsingularity.net>2021-06-29 05:42:18 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-06-29 20:53:54 +0300
commit3b12e7e97938424de2bb1b95ba0bd6a49bad39f9 (patch)
tree8950f0935651b627b186eb44eb56854e07bff962 /mm/page_alloc.c
parent04f8cfeaed0849e702278378bce3867577ca45fb (diff)
downloadlinux-3b12e7e97938424de2bb1b95ba0bd6a49bad39f9.tar.xz
mm/page_alloc: scale the number of pages that are batch freed
When a task is freeing a large number of order-0 pages, it may acquire the zone->lock multiple times freeing pages in batches. This may unnecessarily contend on the zone lock when freeing very large number of pages. This patch adapts the size of the batch based on the recent pattern to scale the batch size for subsequent frees. As the machines I used were not large enough to test this are not large enough to illustrate a problem, a debugging patch shows patterns like the following (slightly editted for clarity) Baseline vanilla kernel time-unmap-14426 [...] free_pcppages_bulk: free 63 count 378 high 378 time-unmap-14426 [...] free_pcppages_bulk: free 63 count 378 high 378 time-unmap-14426 [...] free_pcppages_bulk: free 63 count 378 high 378 time-unmap-14426 [...] free_pcppages_bulk: free 63 count 378 high 378 time-unmap-14426 [...] free_pcppages_bulk: free 63 count 378 high 378 With patches time-unmap-7724 [...] free_pcppages_bulk: free 126 count 814 high 814 time-unmap-7724 [...] free_pcppages_bulk: free 252 count 814 high 814 time-unmap-7724 [...] free_pcppages_bulk: free 504 count 814 high 814 time-unmap-7724 [...] free_pcppages_bulk: free 751 count 814 high 814 time-unmap-7724 [...] free_pcppages_bulk: free 751 count 814 high 814 Link: https://lkml.kernel.org/r/20210525080119.5455-5-mgorman@techsingularity.net Signed-off-by: Mel Gorman <mgorman@techsingularity.net> Acked-by: Dave Hansen <dave.hansen@linux.intel.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Hillf Danton <hdanton@sina.com> Cc: Michal Hocko <mhocko@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/page_alloc.c')
-rw-r--r--mm/page_alloc.c41
1 files changed, 39 insertions, 2 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8d196a803820..e1d1825a2611 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3278,18 +3278,47 @@ static bool free_unref_page_prepare(struct page *page, unsigned long pfn)
return true;
}
+static int nr_pcp_free(struct per_cpu_pages *pcp, int high, int batch)
+{
+ int min_nr_free, max_nr_free;
+
+ /* Check for PCP disabled or boot pageset */
+ if (unlikely(high < batch))
+ return 1;
+
+ /* Leave at least pcp->batch pages on the list */
+ min_nr_free = batch;
+ max_nr_free = high - batch;
+
+ /*
+ * Double the number of pages freed each time there is subsequent
+ * freeing of pages without any allocation.
+ */
+ batch <<= pcp->free_factor;
+ if (batch < max_nr_free)
+ pcp->free_factor++;
+ batch = clamp(batch, min_nr_free, max_nr_free);
+
+ return batch;
+}
+
static void free_unref_page_commit(struct page *page, unsigned long pfn,
int migratetype)
{
struct zone *zone = page_zone(page);
struct per_cpu_pages *pcp;
+ int high;
__count_vm_event(PGFREE);
pcp = this_cpu_ptr(zone->per_cpu_pageset);
list_add(&page->lru, &pcp->lists[migratetype]);
pcp->count++;
- if (pcp->count >= READ_ONCE(pcp->high))
- free_pcppages_bulk(zone, READ_ONCE(pcp->batch), pcp);
+ high = READ_ONCE(pcp->high);
+ if (pcp->count >= high) {
+ int batch = READ_ONCE(pcp->batch);
+
+ free_pcppages_bulk(zone, nr_pcp_free(pcp, high, batch), pcp);
+ }
}
/*
@@ -3541,7 +3570,14 @@ static struct page *rmqueue_pcplist(struct zone *preferred_zone,
unsigned long flags;
local_lock_irqsave(&pagesets.lock, flags);
+
+ /*
+ * On allocation, reduce the number of pages that are batch freed.
+ * See nr_pcp_free() where free_factor is increased for subsequent
+ * frees.
+ */
pcp = this_cpu_ptr(zone->per_cpu_pageset);
+ pcp->free_factor >>= 1;
list = &pcp->lists[migratetype];
page = __rmqueue_pcplist(zone, migratetype, alloc_flags, pcp, list);
local_unlock_irqrestore(&pagesets.lock, flags);
@@ -6737,6 +6773,7 @@ static void per_cpu_pages_init(struct per_cpu_pages *pcp, struct per_cpu_zonesta
*/
pcp->high = BOOT_PAGESET_HIGH;
pcp->batch = BOOT_PAGESET_BATCH;
+ pcp->free_factor = 0;
}
static void __zone_set_pageset_high_and_batch(struct zone *zone, unsigned long high,