Re: [v2 PATCH 2/2] mm: mempolicy: handle vma with unmovable pages mapped correctly in mbind

Yang Shi
2019-07-16T17:29:19Z

On 7/16/19 5:07 AM, Vlastimil Babka wrote:
> On 6/22/19 2:20 AM, Yang Shi wrote:
>> @@ -969,10 +975,21 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
>> /*
>> * page migration, thp tail pages can be passed.
>> */
>> -static void migrate_page_add(struct page *page, struct list_head *pagelist,
>> +static int migrate_page_add(struct page *page, struct list_head *pagelist,
>> unsigned long flags)
>> {
>> struct page *head = compound_head(page);
>> +
>> + /*
>> + * Non-movable page may reach here. And, there may be
>> + * temporaty off LRU pages or non-LRU movable pages.
>> + * Treat them as unmovable pages since they can't be
>> + * isolated, so they can't be moved at the moment. It
>> + * should return -EIO for this case too.
>> + */
>> + if (!PageLRU(head) && (flags & MPOL_MF_STRICT))
>> + return -EIO;
>> +
> Hm but !PageLRU() is not the only way why queueing for migration can
> fail, as can be seen from the rest of the function. Shouldn't all cases
> be reported?

Do you mean the shared pages and isolation failed pages? I'm not sure
whether we should consider these cases break the semantics or not, so I
leave them as they are. But, strictly speaking they should be reported
too, at least for the isolation failed page.

Thanks,
Yang

>
>> /*
>> * Avoid migrating a page that is shared with others.
>> */
>> @@ -984,6 +1001,8 @@ static void migrate_page_add(struct page *page, struct list_head *pagelist,
>> hpage_nr_pages(head));
>> }
>> }
>> +
>> + return 0;
>> }
>>
>> /* page allocation callback for NUMA node migration */
>> @@ -1186,9 +1205,10 @@ static struct page *new_page(struct page *page, unsigned long start)
>> }
>> #else
>>
>> -static void migrate_page_add(struct page *page, struct list_head *pagelist,
>> +static int migrate_page_add(struct page *page, struct list_head *pagelist,
>> unsigned long flags)
>> {
>> + return -EIO;
>> }
>>
>> int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
>>