On 2013/8/2 2:59, Cody P Schafer wrote:
> On 08/01/2013 02:18 AM, Xishi Qiu wrote:
>> __offline_pages()
>> start_isolate_page_range()
>> set_migratetype_isolate()
>> set_pageblock_migratetype() -> this pageblock will be marked as
>> MIGRATE_ISOLATE
>> move_freepages_block() -> pages in PageBuddy will be moved into
>> MIGRATE_ISOLATE list
>> drain_all_pages() -> drain PCP
>> free_pcppages_bulk()
>> mt = get_freepage_migratetype(page); -> PCP's migratetype is
>> not MIGRATE_ISOLATE
>> __free_one_page(page, zone, 0, mt); -> so PCP will not be
>> freed into into MIGRATE_ISOLATE list
>>
>> In this case, the PCP may be allocated again, because they are not in
>> PageBuddy's MIGRATE_ISOLATE list. This will cause offline_pages failed.
>>
>> Signed-off-by: Xishi Qiu <qiuxi...@huawei.com>
>> ---
>> mm/page_alloc.c | 10 ++++++----
>> mm/page_isolation.c | 15 ++++++++++++++-
>> 2 files changed, 20 insertions(+), 5 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index b100255..d873471 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -965,11 +965,13 @@ int move_freepages(struct zone *zone,
>> }
>>
>> order = page_order(page);
>> - list_move(&page->lru,
>> - &zone->free_area[order].free_list[migratetype]);
>> - set_freepage_migratetype(page, migratetype);
>> + if (get_freepage_migratetype(page) != migratetype) {
>> + list_move(&page->lru,
>> + &zone->free_area[order].free_list[migratetype]);
>> + set_freepage_migratetype(page, migratetype);
>> + pages_moved += 1 << order;
>> + }
>> page += 1 << order;
>> - pages_moved += 1 << order;
>
> So this looks like it changes the return from move_freepages() to be the
> "pages moved" from "the pages now belonging to the passed migrate type".
>
> The user of move_freepages_block()'s return value (and thus the return value
> of move_freepages()) in mm/page_alloc.c expects that it is the original
> meaning. The users in page_isolation.c expect it is the new meaning. Those
> need to be reconciled.
>
>> }
>>
>> return pages_moved;
>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
>> index 383bdbb..ba1afc9 100644
>> --- a/mm/page_isolation.c
>> +++ b/mm/page_isolation.c
>> @@ -65,8 +65,21 @@ out:
>> }
>>
>> spin_unlock_irqrestore(&zone->lock, flags);
>> - if (!ret)
>> +
>> + if (!ret) {
>> drain_all_pages();
>> + /*
>> + * When drain_all_pages() frees cached pages into the buddy
>> + * system, it uses the stale migratetype cached in the
>> + * page->index field, so try to move free pages to ISOLATE
>> + * list again.
>> + */
>> + spin_lock_irqsave(&zone->lock, flags);
>> + nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE);
>> + __mod_zone_freepage_state(zone, -nr_pages, migratetype);
>> + spin_unlock_irqrestore(&zone->lock, flags);
>> + }
>> +
>
> Could we teach drain_all_pages() to use the right migrate type instead (or
> add something similar that does)? (pages could be reallocated between the
> drain_all_pages() and move_freepages_block()).
>
Sorry, I made a mistake. __test_page_isolated_in_pageblock() will catch the
pages and move
them into MIGRATE_ISOLATE list. So the code is right.
Thanks,
Xishi Qiu
>> return ret;
>> }
>>
>
> .
>
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