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 15:11:05 +0100 |
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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 :) )
-- Thanks,
David / dhildenb
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