From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Subject: mm/page_alloc: free pages in a single pass during bulk free
free_pcppages_bulk() has taken two passes through the pcp lists since
commit 0a5f4e5b4562 ("mm/free_pcppages_bulk: do not hold lock when picking
pages to free") due to deferring the cost of selecting PCP lists until the
zone lock is held. Now that list selection is simplier, the main cost
during selection is bulkfree_pcp_prepare() which in the normal case is a
simple check and prefetching. As the list manipulations have cost in
itself, go back to freeing pages in a single pass.
The series up to this point was evaulated using a trunc microbenchmark
that is truncating sparse files stored in page cache (mmtests config
config-io-trunc). Sparse files were used to limit filesystem interaction.
The results versus a revert of storing high-order pages in the PCP lists
is
1-socket Skylake
5.17.0-rc3 5.17.0-rc3 5.17.0-rc3
vanilla mm-reverthighpcp-v1 mm-highpcpopt-v2
Min elapsed 540.00 ( 0.00%) 530.00 ( 1.85%) 530.00 ( 1.85%)
Amean elapsed 543.00 ( 0.00%) 530.00 * 2.39%* 530.00 * 2.39%*
Stddev elapsed 4.83 ( 0.00%) 0.00 ( 100.00%) 0.00 ( 100.00%)
CoeffVar elapsed 0.89 ( 0.00%) 0.00 ( 100.00%) 0.00 ( 100.00%)
Max elapsed 550.00 ( 0.00%) 530.00 ( 3.64%) 530.00 ( 3.64%)
BAmean-50 elapsed 540.00 ( 0.00%) 530.00 ( 1.85%) 530.00 ( 1.85%)
BAmean-95 elapsed 542.22 ( 0.00%) 530.00 ( 2.25%) 530.00 ( 2.25%)
BAmean-99 elapsed 542.22 ( 0.00%) 530.00 ( 2.25%) 530.00 ( 2.25%)
2-socket CascadeLake
5.17.0-rc3 5.17.0-rc3 5.17.0-rc3
vanilla mm-reverthighpcp-v1 mm-highpcpopt-v2
Min elapsed 510.00 ( 0.00%) 500.00 ( 1.96%) 500.00 ( 1.96%)
Amean elapsed 529.00 ( 0.00%) 521.00 ( 1.51%) 510.00 * 3.59%*
Stddev elapsed 16.63 ( 0.00%) 12.87 ( 22.64%) 11.55 ( 30.58%)
CoeffVar elapsed 3.14 ( 0.00%) 2.47 ( 21.46%) 2.26 ( 27.99%)
Max elapsed 550.00 ( 0.00%) 540.00 ( 1.82%) 530.00 ( 3.64%)
BAmean-50 elapsed 516.00 ( 0.00%) 512.00 ( 0.78%) 500.00 ( 3.10%)
BAmean-95 elapsed 526.67 ( 0.00%) 518.89 ( 1.48%) 507.78 ( 3.59%)
BAmean-99 elapsed 526.67 ( 0.00%) 518.89 ( 1.48%) 507.78 ( 3.59%)
The original motivation for multi-passes was will-it-scale page_fault1
using $nr_cpu processes.
2-socket CascadeLake (40 cores, 80 CPUs HT enabled)
5.17.0-rc3 5.17.0-rc3
vanilla mm-highpcpopt-v2
Hmean page_fault1-processes-2 2694662.26 ( 0.00%) 2695780.35 ( 0.04%)
Hmean page_fault1-processes-5 6425819.34 ( 0.00%) 6435544.57 * 0.15%*
Hmean page_fault1-processes-8 9642169.10 ( 0.00%) 9658962.39 ( 0.17%)
Hmean page_fault1-processes-12 12167502.10 ( 0.00%) 12190163.79 ( 0.19%)
Hmean page_fault1-processes-21 15636859.03 ( 0.00%) 15612447.26 ( -0.16%)
Hmean page_fault1-processes-30 25157348.61 ( 0.00%) 25169456.65 ( 0.05%)
Hmean page_fault1-processes-48 27694013.85 ( 0.00%) 27671111.46 ( -0.08%)
Hmean page_fault1-processes-79 25928742.64 ( 0.00%) 25934202.02 ( 0.02%) <--
Hmean page_fault1-processes-110 25730869.75 ( 0.00%) 25671880.65 * -0.23%*
Hmean page_fault1-processes-141 25626992.42 ( 0.00%) 25629551.61 ( 0.01%)
Hmean page_fault1-processes-172 25611651.35 ( 0.00%) 25614927.99 ( 0.01%)
Hmean page_fault1-processes-203 25577298.75 ( 0.00%) 25583445.59 ( 0.02%)
Hmean page_fault1-processes-234 25580686.07 ( 0.00%) 25608240.71 ( 0.11%)
Hmean page_fault1-processes-265 25570215.47 ( 0.00%) 25568647.58 ( -0.01%)
Hmean page_fault1-processes-296 25549488.62 ( 0.00%) 25543935.00 ( -0.02%)
Hmean page_fault1-processes-320 25555149.05 ( 0.00%) 25575696.74 ( 0.08%)
The differences are mostly within the noise and the difference close to
$nr_cpus is negligible.
Link: https://lkml.kernel.org/r/20220217002227.5739-6-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
Tested-by: Aaron Lu <aaron.lu@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 56 +++++++++++++++++-----------------------------
1 file changed, 21 insertions(+), 35 deletions(-)
--- a/mm/page_alloc.c~mm-page_alloc-free-pages-in-a-single-pass-during-bulk-free
+++ a/mm/page_alloc.c
@@ -1452,8 +1452,7 @@ static void free_pcppages_bulk(struct zo
unsigned int order;
int prefetch_nr = READ_ONCE(pcp->batch);
bool isolated_pageblocks;
- struct page *page, *tmp;
- LIST_HEAD(head);
+ struct page *page;
/*
* Ensure proper count is passed which otherwise would stuck in the
@@ -1464,6 +1463,13 @@ static void free_pcppages_bulk(struct zo
/* Ensure requested pindex is drained first. */
pindex = pindex - 1;
+ /*
+ * local_lock_irq held so equivalent to spin_lock_irqsave for
+ * both PREEMPT_RT and non-PREEMPT_RT configurations.
+ */
+ spin_lock(&zone->lock);
+ isolated_pageblocks = has_isolate_pageblock(zone);
+
while (count > 0) {
struct list_head *list;
int nr_pages;
@@ -1486,7 +1492,11 @@ static void free_pcppages_bulk(struct zo
nr_pages = 1 << order;
BUILD_BUG_ON(MAX_ORDER >= (1<<NR_PCP_ORDER_WIDTH));
do {
+ int mt;
+
page = list_last_entry(list, struct page, lru);
+ mt = get_pcppage_migratetype(page);
+
/* must delete to avoid corrupting pcp list */
list_del(&page->lru);
count -= nr_pages;
@@ -1495,12 +1505,6 @@ static void free_pcppages_bulk(struct zo
if (bulkfree_pcp_prepare(page))
continue;
- /* Encode order with the migratetype */
- page->index <<= NR_PCP_ORDER_WIDTH;
- page->index |= order;
-
- list_add_tail(&page->lru, &head);
-
/*
* We are going to put the page back to the global
* pool, prefetch its buddy to speed up later access
@@ -1514,36 +1518,18 @@ static void free_pcppages_bulk(struct zo
prefetch_buddy(page, order);
prefetch_nr--;
}
- } while (count > 0 && !list_empty(list));
- }
- /*
- * local_lock_irq held so equivalent to spin_lock_irqsave for
- * both PREEMPT_RT and non-PREEMPT_RT configurations.
- */
- spin_lock(&zone->lock);
- isolated_pageblocks = has_isolate_pageblock(zone);
+ /* MIGRATE_ISOLATE page should not go to pcplists */
+ VM_BUG_ON_PAGE(is_migrate_isolate(mt), page);
+ /* Pageblock could have been isolated meanwhile */
+ if (unlikely(isolated_pageblocks))
+ mt = get_pageblock_migratetype(page);
- /*
- * Use safe version since after __free_one_page(),
- * page->lru.next will not point to original list.
- */
- list_for_each_entry_safe(page, tmp, &head, lru) {
- int mt = get_pcppage_migratetype(page);
-
- /* mt has been encoded with the order (see above) */
- order = mt & NR_PCP_ORDER_MASK;
- mt >>= NR_PCP_ORDER_WIDTH;
-
- /* MIGRATE_ISOLATE page should not go to pcplists */
- VM_BUG_ON_PAGE(is_migrate_isolate(mt), page);
- /* Pageblock could have been isolated meanwhile */
- if (unlikely(isolated_pageblocks))
- mt = get_pageblock_migratetype(page);
-
- __free_one_page(page, page_to_pfn(page), zone, order, mt, FPI_NONE);
- trace_mm_page_pcpu_drain(page, order, mt);
+ __free_one_page(page, page_to_pfn(page), zone, order, mt, FPI_NONE);
+ trace_mm_page_pcpu_drain(page, order, mt);
+ } while (count > 0 && !list_empty(list));
}
+
spin_unlock(&zone->lock);
}
_
