On 27.11.20 17:54, David Hildenbrand wrote:
> On 27.11.20 15:19, Muchun Song wrote:
>> Current pageblock isolation logic could isolate each pageblock individually
>> since commit d9dddbf55667 ("mm/page_alloc: prevent merging between isolated
>> and other pageblocks"). So we not need to concern about page allocator
>> merges buddies from different pageblocks and changes MIGRATE_ISOLATE to
>> some other migration type.
>>
>> Signed-off-by: Muchun Song <songmuc...@bytedance.com>
>> ---
>> mm/page_alloc.c | 26 ++++++++------------------
>> 1 file changed, 8 insertions(+), 18 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index cefbef32bf4a..608a2c2b8ab7 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -8313,16 +8313,14 @@ struct page *has_unmovable_pages(struct zone *zone,
>> struct page *page,
>> }
>>
>> #ifdef CONFIG_CONTIG_ALLOC
>> -static unsigned long pfn_max_align_down(unsigned long pfn)
>> +static unsigned long pfn_align_down(unsigned long pfn)
>> {
>> - return pfn & ~(max_t(unsigned long, MAX_ORDER_NR_PAGES,
>> - pageblock_nr_pages) - 1);
>> + return pfn & ~(pageblock_nr_pages - 1);
>> }
>>
>> -static unsigned long pfn_max_align_up(unsigned long pfn)
>> +static unsigned long pfn_align_up(unsigned long pfn)
>> {
>> - return ALIGN(pfn, max_t(unsigned long, MAX_ORDER_NR_PAGES,
>> - pageblock_nr_pages));
>> + return ALIGN(pfn, pageblock_nr_pages);
>> }
>>
>> /* [start, end) must belong to a single zone. */
>> @@ -8415,14 +8413,6 @@ int alloc_contig_range(unsigned long start, unsigned
>> long end,
>> INIT_LIST_HEAD(&cc.migratepages);
>>
>> /*
>> - * What we do here is we mark all pageblocks in range as
>> - * MIGRATE_ISOLATE. Because pageblock and max order pages may
>> - * have different sizes, and due to the way page allocator
>> - * work, we align the range to biggest of the two pages so
>> - * that page allocator won't try to merge buddies from
>> - * different pageblocks and change MIGRATE_ISOLATE to some
>> - * other migration type.
>> - *
>> * Once the pageblocks are marked as MIGRATE_ISOLATE, we
>> * migrate the pages from an unaligned range (ie. pages that
>> * we are interested in). This will put all the pages in
>> @@ -8438,8 +8428,8 @@ int alloc_contig_range(unsigned long start, unsigned
>> long end,
>> * put back to page allocator so that buddy can use them.
>> */
>>
>> - ret = start_isolate_page_range(pfn_max_align_down(start),
>> - pfn_max_align_up(end), migratetype, 0);
>> + ret = start_isolate_page_range(pfn_align_down(start), pfn_align_up(end),
>> + migratetype, 0);
>> if (ret)
>> return ret;
>>
>> @@ -8522,8 +8512,8 @@ int alloc_contig_range(unsigned long start, unsigned
>> long end,
>> free_contig_range(end, outer_end - end);
>>
>> done:
>> - undo_isolate_page_range(pfn_max_align_down(start),
>> - pfn_max_align_up(end), migratetype);
>> + undo_isolate_page_range(pfn_align_down(start), pfn_align_up(end),
>> + migratetype);
>> return ret;
>> }
>> EXPORT_SYMBOL(alloc_contig_range);
>>
>
> Last time I checked, set_migratetype_isolate()->has_unmovable_pages()
> was not prepared for that in case of !CMA and !ZONE_MOVABLE.
>
> Assume you have an unmovable MAX_ORDER - 1 page that spans two
> pageblocks (e.g., x86-64). Assume you try to isolate the second
> pageblock. IIRC, you would answer "yes", as the refcount of all involved
> pages is 0.
>
>
> How did you test this works as expected?
>
And I forgot to mention, in case it's a movable MAX_ORDER - 1 page (or
simply free), would __alloc_contig_migrate_range() do the right thing
and migrate the whole page?
--
Thanks,
David / dhildenb
