The patch titled
Subject: mm/page_alloc: simplify how many pages are selected per pcp list during bulk free
has been added to the -mm tree. Its filename is
mm-page_alloc-simplify-how-many-pages-are-selected-per-pcp-list-during-bulk-free.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-page_alloc-simplify-how-many-pages-are-selected-per-pcp-list-during-bulk-free.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-page_alloc-simplify-how-many-pages-are-selected-per-pcp-list-during-bulk-free.patch
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------------------------------------------------------
From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Subject: mm/page_alloc: simplify how many pages are selected per pcp list during bulk free
free_pcppages_bulk() selects pages to free by round-robining between
lists. Originally this was to evenly shrink pages by migratetype but
uneven freeing is inevitable due to high pages. Simplify list selection
by starting with a list that definitely has pages on it in
free_unref_page_commit() and for drain, it does not matter where draining
starts as all pages are removed.
Link: https://lkml.kernel.org/r/20220215145111.27082-4-mgorman@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Aaron Lu <aaron.lu@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 34 +++++++++++-----------------------
1 file changed, 11 insertions(+), 23 deletions(-)
--- a/mm/page_alloc.c~mm-page_alloc-simplify-how-many-pages-are-selected-per-pcp-list-during-bulk-free
+++ a/mm/page_alloc.c
@@ -1447,13 +1447,11 @@ static inline void prefetch_buddy(struct
* count is the number of pages to free.
*/
static void free_pcppages_bulk(struct zone *zone, int count,
- struct per_cpu_pages *pcp)
+ struct per_cpu_pages *pcp,
+ int pindex)
{
- int pindex = 0;
int min_pindex = 0;
int max_pindex = NR_PCP_LISTS - 1;
- int batch_free = 0;
- int nr_freed = 0;
unsigned int order;
int prefetch_nr = READ_ONCE(pcp->batch);
bool isolated_pageblocks;
@@ -1467,16 +1465,10 @@ static void free_pcppages_bulk(struct zo
count = min(pcp->count, count);
while (count > 0) {
struct list_head *list;
+ int nr_pages;
- /*
- * Remove pages from lists in a round-robin fashion. A
- * batch_free count is maintained that is incremented when an
- * empty list is encountered. This is so more pages are freed
- * off fuller lists instead of spinning excessively around empty
- * lists
- */
+ /* Remove pages from lists in a round-robin fashion. */
do {
- batch_free++;
if (++pindex == NR_PCP_LISTS)
pindex = 0;
list = &pcp->lists[pindex];
@@ -1489,18 +1481,15 @@ static void free_pcppages_bulk(struct zo
min_pindex++;
} while (1);
- /* This is the only non-empty list. Free them all. */
- if (batch_free >= max_pindex - min_pindex)
- batch_free = count;
-
order = pindex_to_order(pindex);
+ nr_pages = 1 << order;
BUILD_BUG_ON(MAX_ORDER >= (1<<NR_PCP_ORDER_WIDTH));
do {
page = list_last_entry(list, struct page, lru);
/* must delete to avoid corrupting pcp list */
list_del(&page->lru);
- nr_freed += 1 << order;
- count -= 1 << order;
+ count -= nr_pages;
+ pcp->count -= nr_pages;
if (bulkfree_pcp_prepare(page))
continue;
@@ -1524,9 +1513,8 @@ static void free_pcppages_bulk(struct zo
prefetch_buddy(page, order);
prefetch_nr--;
}
- } while (count > 0 && --batch_free && !list_empty(list));
+ } while (count > 0 && !list_empty(list));
}
- pcp->count -= nr_freed;
/*
* local_lock_irq held so equivalent to spin_lock_irqsave for
@@ -3133,7 +3121,7 @@ void drain_zone_pages(struct zone *zone,
batch = READ_ONCE(pcp->batch);
to_drain = min(pcp->count, batch);
if (to_drain > 0)
- free_pcppages_bulk(zone, to_drain, pcp);
+ free_pcppages_bulk(zone, to_drain, pcp, 0);
local_unlock_irqrestore(&pagesets.lock, flags);
}
#endif
@@ -3154,7 +3142,7 @@ static void drain_pages_zone(unsigned in
pcp = per_cpu_ptr(zone->per_cpu_pageset, cpu);
if (pcp->count)
- free_pcppages_bulk(zone, pcp->count, pcp);
+ free_pcppages_bulk(zone, pcp->count, pcp, 0);
local_unlock_irqrestore(&pagesets.lock, flags);
}
@@ -3435,7 +3423,7 @@ static void free_unref_page_commit(struc
if (pcp->count >= high) {
int batch = READ_ONCE(pcp->batch);
- free_pcppages_bulk(zone, nr_pcp_free(pcp, high, batch), pcp);
+ free_pcppages_bulk(zone, nr_pcp_free(pcp, high, batch), pcp, pindex);
}
}
_
Patches currently in -mm which might be from mgorman@xxxxxxxxxxxxxxxxxxx are
mm-page_alloc-fetch-the-correct-pcp-buddy-during-bulk-free.patch
mm-page_alloc-track-range-of-active-pcp-lists-during-bulk-free.patch
mm-page_alloc-simplify-how-many-pages-are-selected-per-pcp-list-during-bulk-free.patch
mm-page_alloc-free-pages-in-a-single-pass-during-bulk-free.patch
mm-page_alloc-limit-number-of-high-order-pages-on-pcp-during-bulk-free.patch
