On 2/25/20 7:44 PM, Rik van Riel wrote:
>> Also PageTransHuge() is basically just a PageHead() so for each
>> non-hugetlbfs compound page this will assume it's a THP, while
>> correctly
>> it should reach the __PageMovable() || PageLRU(page) tests below.
>>
>> So probably this should do something like.
>>
>> if (PageHuge(page) || PageTransCompound(page)) {
>> ...
>> if (PageHuge(page) && !hpage_migration_supported)) return page.
>
> So far so good.
>
>> if (!PageLRU(head) && !__PageMovable(head)) return page
>
> I don't get this one, though. What about a THP that has
> not made it onto the LRU list yet for some reason?
Uh, is it any different from base pages which have to pass the same check? I
guess the caller could do e.g. lru_add_drain_all() first.
> I don't think anonymous pages are marked __PageMovable,
> are they? It looks like they only have the PAGE_MAPPING_ANON
> flag set, not the PAGE_MAPPING_MOVABLE one.
>
> What am I missing?
My point is that we should not accept compound pages that are neither a
migratable hugetlbfs page nor a THP, as movable. And your PageTransHuge() test
and my PageTransCompound() is really just a test for all compound pages, not
"hugetlbfs or THP only". I should have perhaps suggested PageCompound() instead
of the PageTransCompound() wrapper, to make it more obvious.
So we should test non-hugetlbfs pages first whether they are the kind of
compound pages that are migratable. THP's should pass this test by PageLRU(),
other compound movable pages by __PageMovable(head).
>
>> ...
>>
>> > struct page *head = compound_head(page);
>> > unsigned int skip_pages;
>> >
>> > - if
>> > (!hugepage_migration_supported(page_hstate(head)))
>> > + if (PageHuge(page) &&
>> > + !hugepage_migration_supported(page_hstate(h
>> > ead)))
>> > return page;
>> >
>> > skip_pages = compound_nr(head) - (page - head);
>> >
>>
>>
>
