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

[Wei Yang]

On Mon, Sep 28, 2020 at 08:21:09PM +0200, David Hildenbrand wrote:
>__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@xxxxxxx>
>Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
>Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
>Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
>Cc: Michal Hocko <mhocko@xxxxxxxxxx>
>Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
>Cc: Vlastimil Babka <vbabka@xxxxxxx>
>Cc: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx>
>Cc: Oscar Salvador <osalvador@xxxxxxx>
>Cc: Mike Rapoport <rppt@xxxxxxxxxx>
>Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
>Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
>Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
>Cc: Wei Liu <wei.liu@xxxxxxxxxx>
>Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
>---
> 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

If my code is the latest version.

s/init_single_page/__init_single_page/

Besides this.

Reviewed-by: Wei Yang <richard.weiyang@xxxxxxxxxxxxxxxxx>

>+	 * 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

-- 
Wei Yang
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