__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

> __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)

Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>

On Mon 28-09-20 20:21:09, 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.

It took some time to get through all the freeing paths with subtle
differences but this looks reasonable. You are mentioning that this
influences a boot time free memory ordering as well but only very
briefly. I do not expect this to make a huge difference but who knows.
It makes some sense to add pages in the order they show up in the
physical address ordering.

> 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>

That being said I do not see any fundamental problems.
Acked-by: Michal Hocko <mhocko@suse.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
> 

-- 
Michal Hocko
SUSE Labs

On 02.10.20 15:41, Michal Hocko wrote:
> On Mon 28-09-20 20:21:09, 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.
> 
> It took some time to get through all the freeing paths with subtle
> differences but this looks reasonable. You are mentioning that this
> influences a boot time free memory ordering as well but only very
> briefly. I do not expect this to make a huge difference but who knows.
> It makes some sense to add pages in the order they show up in the
> physical address ordering.

I think boot memory is mostly exposed in the physical address ordering.
In that case, higher addresses will now be used less likely immediately
after this patch. I also don't think it's an issue - if we still detect
it's an issue it's fairly easy to change again.

Thanks!

-- 
Thanks,

David / dhildenb

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@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

If my code is the latest version.

s/init_single_page/__init_single_page/

Besides this.

Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>

>+	 * 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
Help you, Help me

On 29.09.20 11:36, Wei Yang wrote:
> 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@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
> 
> If my code is the latest version.
> 
> s/init_single_page/__init_single_page/

Indeed - thanks!


-- 
Thanks,

David / dhildenb