mm, thp: restore node-local hugepage allocations

Linux Kernel / Linux Kernel - David Rientjes [google.com] - 5 December 2018 23:45 EST

This is a full revert of ac5b2c18911f ("mm: thp: relax __GFP_THISNODE for MADV_HUGEPAGE mappings") and a partial revert of 89c83fb539f9 ("mm, thp: consolidate THP gfp handling into alloc_hugepage_direct_gfpmask").

By not setting __GFP_THISNODE, applications can allocate remote hugepages when the local node is fragmented or low on memory when either the thp defrag setting is "always" or the vma has been madvised with MADV_HUGEPAGE.

Remote access to hugepages often has much higher latency than local pages of the native page size. On Haswell, ac5b2c18911f was shown to have a 13.9% access regression after this commit for binaries that remap their text segment to be backed by transparent hugepages.

The intent of ac5b2c18911f is to address an issue where a local node is low on memory or fragmented such that a hugepage cannot be allocated. In every scenario where this was described as a fix, there is abundant and unfragmented remote memory available to allocate from, even with a greater access latency.

If remote memory is also low or fragmented, not setting __GFP_THISNODE was also measured on Haswell to have a 40% regression in allocation latency.

Restore __GFP_THISNODE for thp allocations.

Fixes: ac5b2c18911f ("mm: thp: relax __GFP_THISNODE for MADV_HUGEPAGE mappings") Fixes: 89c83fb539f9 ("mm, thp: consolidate THP gfp handling into alloc_hugepage_direct_gfpmask") Cc: Andrea Arcangeli Cc: Mel Gorman Cc: Vlastimil Babka Cc: Michal Hocko Cc: Andrew Morton

2f0799a0ffc0 mm, thp: restore node-local hugepage allocations
include/linux/mempolicy.h | 2 --
mm/huge_memory.c | 42 ++++++++++++++++--------------------------
mm/mempolicy.c | 2 +-
3 files changed, 17 insertions(+), 29 deletions(-)

Upstream: git.kernel.org


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