Messages in this thread | | | From | Andrea Arcangeli <> | Subject | [PATCH 0/3] mm: hugetlbfs: fix hugetlbfs optimization v2 | Date | Fri, 15 Nov 2013 18:47:45 +0100 |
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Hi,
1/3 is a bugfix so it should be applied more urgently. 1/3 is not as fast as the current upstream code in the hugetlbfs + directio extreme 8GB/sec benchmark (but 3/3 should fill the gap later). The code is identical to the one I posted in v1 just rebased on upstream and was developed in collaboration with Khalid who already tested it.
2/3 and 3/3 had very little testing yet, and they're incremental optimization. 2/3 is minor and most certainly worth applying later.
3/3 instead complicates things a bit and adds more branches to the THP fast paths, so it should only be applied if the benchmarks of hugetlbfs + directio show that it is very worthwhile (that has not been verified yet). If it's not worthwhile 3/3 should be dropped (and the gap should be filled in some other way if the gap is not caused by the _mapcount mangling as I guessed). Ideally this should bring even more performance than current upstream code, as current upstream code still increased the _mapcount in gup_fast by mistake, while this eliminates the locked op on the tail page cacheline in gup_fast too (which is required for correctness too).
As a side note: the _mapcount refcounting on tail pages is only needed for THP as it is a fundamental information required for split_huge_page_refcount to be able to distribute the head refcounts during the split. And it is done on _mapcount instead of the _count, because the _count would screwup badly with the get_page_unless_zero speculative pagecache accesses.
Andrea Arcangeli (3): mm: hugetlbfs: fix hugetlbfs optimization mm: hugetlb: use get_page_foll in follow_hugetlb_page mm: tail page refcounting optimization for slab and hugetlbfs
include/linux/mm.h | 30 ++++++++- mm/hugetlb.c | 19 +++++- mm/internal.h | 3 +- mm/swap.c | 187 ++++++++++++++++++++++++++++++++++------------------- 4 files changed, 170 insertions(+), 69 deletions(-)
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