[PATCH v1 4/5] mm/page_alloc: place pages to tail in __free_pages_core()

David Hildenbrand
2020-09-28T18:21:51Z

__free_pages_core() is used when exposing fresh memory to the buddy
during system boot and when onlining memory in generic_online_page().

generic_online_page() is used in two cases:

1. Direct memory onlining in online_pages().
2. Deferred memory onlining in memory-ballooning-like mechanisms (HyperV
balloon and virtio-mem), when parts of a section are kept
fake-offline to be fake-onlined later on.

In 1, we already place pages to the tail of the freelist. Pages will be
freed to MIGRATE_ISOLATE lists first and moved to the tail of the freelists
via undo_isolate_page_range().

In 2, we currently don't implement a proper rule. In case of virtio-mem,
where we currently always online MAX_ORDER - 1 pages, the pages will be
placed to the HEAD of the freelist - undesireable. While the hyper-v
balloon calls generic_online_page() with single pages, usually it will
call it on successive single pages in a larger block.

The pages are fresh, so place them to the tail of the freelists and avoid
the PCP. In __free_pages_core(), remove the now superflouos call to
set_page_refcounted() and add a comment regarding page initialization and
the refcount.

Note: In 2. we currently don't shuffle. If ever relevant (page shuffling
is usually of limited use in virtualized environments), we might want to
shuffle after a sequence of generic_online_page() calls in the
relevant callers.

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
mm/page_alloc.c | 37 ++++++++++++++++++++++++-------------
1 file changed, 24 insertions(+), 13 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d5a5f528b8ca..8a2134fe9947 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -270,7 +270,8 @@ bool pm_suspended_storage(void)
unsigned int pageblock_order __read_mostly;
#endif

-static void __free_pages_ok(struct page *page, unsigned int order);
+static void __free_pages_ok(struct page *page, unsigned int order,
+ fop_t fop_flags);

/*
* results with 256, 32 in the lowmem_reserve sysctl:
@@ -682,7 +683,7 @@ static void bad_page(struct page *page, const char *reason)
void free_compound_page(struct page *page)
{
mem_cgroup_uncharge(page);
- __free_pages_ok(page, compound_order(page));
+ __free_pages_ok(page, compound_order(page), FOP_NONE);
}

void prep_compound_page(struct page *page, unsigned int order)
@@ -1419,17 +1420,15 @@ static void free_pcppages_bulk(struct zone *zone, int count,
spin_unlock(&zone->lock);
}

-static void free_one_page(struct zone *zone,
- struct page *page, unsigned long pfn,
- unsigned int order,
- int migratetype)
+static void free_one_page(struct zone *zone, struct page *page, unsigned long pfn,
+ unsigned int order, int migratetype, fop_t fop_flags)
{
spin_lock(&zone->lock);
if (unlikely(has_isolate_pageblock(zone) ||
is_migrate_isolate(migratetype))) {
migratetype = get_pfnblock_migratetype(page, pfn);
}
- __free_one_page(page, pfn, zone, order, migratetype, FOP_NONE);
+ __free_one_page(page, pfn, zone, order, migratetype, fop_flags);
spin_unlock(&zone->lock);
}

@@ -1507,7 +1506,8 @@ void __meminit reserve_bootmem_region(phys_addr_t start, phys_addr_t end)
}
}

-static void __free_pages_ok(struct page *page, unsigned int order)
+static void __free_pages_ok(struct page *page, unsigned int order,
+ fop_t fop_flags)
{
unsigned long flags;
int migratetype;
@@ -1519,7 +1519,8 @@ static void __free_pages_ok(struct page *page, unsigned int order)
migratetype = get_pfnblock_migratetype(page, pfn);
local_irq_save(flags);
__count_vm_events(PGFREE, 1 << order);
- free_one_page(page_zone(page), page, pfn, order, migratetype);
+ free_one_page(page_zone(page), page, pfn, order, migratetype,
+ fop_flags);
local_irq_restore(flags);
}

@@ -1529,6 +1530,11 @@ void __free_pages_core(struct page *page, unsigned int order)
struct page *p = page;
unsigned int loop;

+ /*
+ * When initializing the memmap, init_single_page() sets the refcount
+ * of all pages to 1 ("allocated"/"not free"). We have to set the
+ * refcount of all involved pages to 0.
+ */
prefetchw(p);
for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
prefetchw(p + 1);
@@ -1539,8 +1545,12 @@ void __free_pages_core(struct page *page, unsigned int order)
set_page_count(p, 0);

atomic_long_add(nr_pages, &page_zone(page)->managed_pages);
- set_page_refcounted(page);
- __free_pages(page, order);
+
+ /*
+ * Bypass PCP and place fresh pages right to the tail, primarily
+ * relevant for memory onlining.
+ */
+ __free_pages_ok(page, order, FOP_TO_TAIL);
}

#ifdef CONFIG_NEED_MULTIPLE_NODES
@@ -3171,7 +3181,8 @@ static void free_unref_page_commit(struct page *page, unsigned long pfn)
*/
if (migratetype >= MIGRATE_PCPTYPES) {
if (unlikely(is_migrate_isolate(migratetype))) {
- free_one_page(zone, page, pfn, 0, migratetype);
+ free_one_page(zone, page, pfn, 0, migratetype,
+ FOP_NONE);
return;
}
migratetype = MIGRATE_MOVABLE;
@@ -5063,7 +5074,7 @@ static inline void free_the_page(struct page *page, unsigned int order)
if (order == 0) /* Via pcp? */
free_unref_page(page);
else
- __free_pages_ok(page, order);
+ __free_pages_ok(page, order, FOP_NONE);
}

void __free_pages(struct page *page, unsigned int order)
--
2.26.2