Date:   Tue, 29 Sep 2020 12:14:42 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Wei Yang <richard.weiyang@...ux.alibaba.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-hyperv@...r.kernel.org, xen-devel@...ts.xenproject.org,
        linux-acpi@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Oscar Salvador <osalvador@...e.de>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Mike Rapoport <rppt@...nel.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>
Subject: Re: [PATCH v1 4/5] mm/page_alloc: place pages to tail in
 __free_pages_core()

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@...e.cz>
>> Reviewed-by: Oscar Salvador <osalvador@...e.de>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
>> Cc: Mel Gorman <mgorman@...hsingularity.net>
>> Cc: Michal Hocko <mhocko@...nel.org>
>> Cc: Dave Hansen <dave.hansen@...el.com>
>> Cc: Vlastimil Babka <vbabka@...e.cz>
>> Cc: Wei Yang <richard.weiyang@...ux.alibaba.com>
>> Cc: Oscar Salvador <osalvador@...e.de>
>> Cc: Mike Rapoport <rppt@...nel.org>
>> Cc: "K. Y. Srinivasan" <kys@...rosoft.com>
>> Cc: Haiyang Zhang <haiyangz@...rosoft.com>
>> Cc: Stephen Hemminger <sthemmin@...rosoft.com>
>> Cc: Wei Liu <wei.liu@...nel.org>
>> Signed-off-by: David Hildenbrand <david@...hat.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

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