Messages in this thread |  | | Subject | Re: [RFC PATCH 1/2] mm,page_alloc: Make alloc_contig_range handle in-use hugetlb pages | From | David Hildenbrand <> | Date | Wed, 10 Feb 2021 15:22:07 +0100 |
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On 10.02.21 15:14, Oscar Salvador wrote: > On Wed, Feb 10, 2021 at 03:11:05PM +0100, David Hildenbrand wrote: >> On 10.02.21 15:09, Oscar Salvador wrote: >>> On Wed, Feb 10, 2021 at 09:56:37AM +0100, David Hildenbrand wrote: >>>> On 08.02.21 11:38, Oscar Salvador wrote: >>>>> alloc_contig_range is not prepared to handle hugetlb pages and will >>>>> fail if it ever sees one, but since they can be migrated as any other >>>>> page (LRU and Movable), it makes sense to also handle them. >>>>> >>>>> For now, do it only when coming from alloc_contig_range. >>>>> >>>>> Signed-off-by: Oscar Salvador <osalvador@suse.de> >>>>> --- >>>>> mm/compaction.c | 17 +++++++++++++++++ >>>>> mm/vmscan.c | 5 +++-- >>>>> 2 files changed, 20 insertions(+), 2 deletions(-) >>>>> >>>>> diff --git a/mm/compaction.c b/mm/compaction.c >>>>> index e5acb9714436..89cd2e60da29 100644 >>>>> --- a/mm/compaction.c >>>>> +++ b/mm/compaction.c >>>>> @@ -940,6 +940,22 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, >>>>> goto isolate_fail; >>>>> } >>>>> + /* >>>>> + * Handle hugetlb pages only when coming from alloc_contig >>>>> + */ >>>>> + if (PageHuge(page) && cc->alloc_contig) { >>>>> + if (page_count(page)) { >>>> >>>> I wonder if we should care about races here. What if someone concurrently >>>> allocates/frees? >>>> >>>> Note that PageHuge() succeeds on tail pages, isolate_huge_page() not, i >>>> assume we'll have to handle that as well. >>>> >>>> I wonder if it would make sense to move some of the magic to hugetlb code >>>> and handle it there with less chances for races (isolate if used, >>>> alloc-and-dissolve if not). >>> >>> Yes, it makes sense to keep the magic in hugetlb code. >>> Note, though, that removing all races might be tricky. >>> >>> isolate_huge_page() checks for PageHuge under hugetlb_lock, >>> so there is a race between a call to PageHuge(x) and a subsequent >>> call to isolate_huge_page(). >>> But we should be fine as isolate_huge_page will fail in case the page is >>> no longer HugeTLB. >>> >>> Also, since isolate_migratepages_block() gets called with ranges >>> pageblock aligned, we should never be handling tail pages in the core >>> of the function. E.g: the same way we handle THP: >> >> Gigantic pages? (spoiler: see my comments to next patch :) ) > > Oh, yeah, that sucks. > We had the same problem in scan_movable_pages/has_unmovable_pages > with such pages. > > Uhm, I will try to be more careful :-) >
Gigantic pages are a minefield. Not your fault :)
-- Thanks,
David / dhildenb
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