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Message-ID: <4640ADF8-F5F3-4CEF-A849-8F8C28F17DD0@nvidia.com>
Date: Fri, 10 Dec 2021 10:39:58 -0500
From: Zi Yan <ziy@...dia.com>
To: Eric Ren <renzhengeek@...il.com>
Cc: David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Michael Ellerman <mpe@...erman.id.au>,
Christoph Hellwig <hch@....de>,
Marek Szyprowski <m.szyprowski@...sung.com>,
Robin Murphy <robin.murphy@....com>,
linuxppc-dev@...ts.ozlabs.org,
virtualization@...ts.linux-foundation.org,
iommu@...ts.linux-foundation.org, Vlastimil Babka <vbabka@...e.cz>,
Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [RFC PATCH v2 1/7] mm: page_alloc: avoid merging non-fallbackable pageblocks with others.
Hi Eric,
Thanks for looking into my patch.
On 10 Dec 2021, at 2:43, Eric Ren wrote:
> Hi,
>
> On 2021/12/10 07:04, Zi Yan wrote:
>> From: Zi Yan <ziy@...dia.com>
>>
>> This is done in addition to MIGRATE_ISOLATE pageblock merge avoidance.
>> It prepares for the upcoming removal of the MAX_ORDER-1 alignment
>> requirement for CMA and alloc_contig_range().
>>
>> MIGRARTE_HIGHATOMIC should not merge with other migratetypes like
>> MIGRATE_ISOLATE and MIGRARTE_CMA[1], so this commit prevents that too.
>> Also add MIGRARTE_HIGHATOMIC to fallbacks array for completeness.
>>
>> [1] https://lore.kernel.org/linux-mm/20211130100853.GP3366@techsingularity.net/
>>
>> Signed-off-by: Zi Yan <ziy@...dia.com>
>> ---
>> include/linux/mmzone.h | 6 ++++++
>> mm/page_alloc.c | 28 ++++++++++++++++++----------
>> 2 files changed, 24 insertions(+), 10 deletions(-)
>>
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index 58e744b78c2c..b925431b0123 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -83,6 +83,12 @@ static inline bool is_migrate_movable(int mt)
>> return is_migrate_cma(mt) || mt == MIGRATE_MOVABLE;
>> }
>> +/* See fallbacks[MIGRATE_TYPES][3] in page_alloc.c */
>> +static inline bool migratetype_has_fallback(int mt)
>> +{
>> + return mt < MIGRATE_PCPTYPES;
>> +}
>> +
>
> I would suggest spliting the patch into 2 parts. The first part: no functioning change, just introduce migratetype_has_fallback()
> and replace where it applys to.
OK. I can do that.
>
>> #define for_each_migratetype_order(order, type) \
>> for (order = 0; order < MAX_ORDER; order++) \
>> for (type = 0; type < MIGRATE_TYPES; type++)
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index edfd6c81af82..107a5f186d3b 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1041,6 +1041,12 @@ buddy_merge_likely(unsigned long pfn, unsigned long buddy_pfn,
>> return page_is_buddy(higher_page, higher_buddy, order + 1);
>> }
>> +static inline bool has_non_fallback_pageblock(struct zone *zone)
>> +{
>> + return has_isolate_pageblock(zone) || zone_cma_pages(zone) != 0 ||
>> + zone->nr_reserved_highatomic != 0;
>
> Make zone->nr_reserved_highatomic != 0 a helper as zone_cma_pages()?
I am not sure. We have zone_cma_pages() because when CMA is not enabled, 0 can be
simply returned. But MIGRATE_HIGHATOMIC is always present, then an helper function
is not that useful.
>> +}
>> +
>> /*
>> * Freeing function for a buddy system allocator.
>> *
>> @@ -1116,14 +1122,15 @@ static inline void __free_one_page(struct page *page,
>> }
>> if (order < MAX_ORDER - 1) {
>> /* If we are here, it means order is >= pageblock_order.
>> - * We want to prevent merge between freepages on isolate
>> - * pageblock and normal pageblock. Without this, pageblock
>> - * isolation could cause incorrect freepage or CMA accounting.
>> + * We want to prevent merge between freepages on pageblock
>> + * without fallbacks and normal pageblock. Without this,
>> + * pageblock isolation could cause incorrect freepage or CMA
>> + * accounting or HIGHATOMIC accounting.
>> *
>> * We don't want to hit this code for the more frequent
>> * low-order merging.
>> */
>> - if (unlikely(has_isolate_pageblock(zone))) {
>> + if (unlikely(has_non_fallback_pageblock(zone))) {
> I'm not familiar with the code details, just wondering if this change would has side effects on cma
> pageblock merging as it the condition stronger?
No impact on cma pageblock merging, AFAICT.
>
> Thanks,
> Eric
>> int buddy_mt;
>> buddy_pfn = __find_buddy_pfn(pfn, order);
>> @@ -1131,8 +1138,8 @@ static inline void __free_one_page(struct page *page,
>> buddy_mt = get_pageblock_migratetype(buddy);
>> if (migratetype != buddy_mt
>> - && (is_migrate_isolate(migratetype) ||
>> - is_migrate_isolate(buddy_mt)))
>> + && (!migratetype_has_fallback(migratetype) ||
>> + !migratetype_has_fallback(buddy_mt)))
>> goto done_merging;
>> }
>> max_order = order + 1;
>> @@ -2483,6 +2490,7 @@ static int fallbacks[MIGRATE_TYPES][3] = {
>> [MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE, MIGRATE_TYPES },
>> [MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_TYPES },
>> [MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE, MIGRATE_TYPES },
>> + [MIGRATE_HIGHATOMIC] = { MIGRATE_TYPES }, /* Never used */
>> #ifdef CONFIG_CMA
>> [MIGRATE_CMA] = { MIGRATE_TYPES }, /* Never used */
>> #endif
>> @@ -2794,8 +2802,8 @@ static void reserve_highatomic_pageblock(struct page *page, struct zone *zone,
>> /* Yoink! */
>> mt = get_pageblock_migratetype(page);
>> - if (!is_migrate_highatomic(mt) && !is_migrate_isolate(mt)
>> - && !is_migrate_cma(mt)) {
>> + /* Only reserve normal pageblock */
>> + if (migratetype_has_fallback(mt)) {
>> zone->nr_reserved_highatomic += pageblock_nr_pages;
>> set_pageblock_migratetype(page, MIGRATE_HIGHATOMIC);
>> move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, NULL);
>> @@ -3544,8 +3552,8 @@ int __isolate_free_page(struct page *page, unsigned int order)
>> struct page *endpage = page + (1 << order) - 1;
>> for (; page < endpage; page += pageblock_nr_pages) {
>> int mt = get_pageblock_migratetype(page);
>> - if (!is_migrate_isolate(mt) && !is_migrate_cma(mt)
>> - && !is_migrate_highatomic(mt))
>> + /* Only change normal pageblock */
>> + if (migratetype_has_fallback(mt))
>> set_pageblock_migratetype(page,
>> MIGRATE_MOVABLE);
>> }
--
Best Regards,
Yan, Zi
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