Eric B Munson wrote: > It is true that you will end up with huge pages for the heap eventually > without > changing anything. khugepaged will promote areas it finds that are 2MB > aligned, etc. However, it is possible to have things _allocated_ as > transparent huge pages without requiring promotion. To do this, the > allocation > needs to be 2MB aligned. This is what morecore=thp does, it ensures that > _all_ > heap allocations start life as transparent huge pages and will not require > promotion unless they are split. > > I am fine changing the morecore option to be thp and thp+ (or maybe just > madvise) where the latter implies thp. I do think that having thp without > madvise is useful for the reasons stated above.
Maybe we should look at where HUGETLB_MORECORE=thp (as currently proposed) adds value. 1. /sys/kernel/mm/transparent_hugepage/enabled = never. HUGETLB_MORECORE=thp adds no value. Arguably, it makes things worse by putting a gap in the heap. 2. /sys/kernel/mm/transparent_hugepage/enabled = madvise. HUGETLB_MORECORE=thp adds no value unless HUGETLB_THP_MADVISE is set. If HUGETLB_THP_MADVISE is _not_ set, arguably makes things worse by putting a gap in the heap. If HUGETLB_THP_MADVISE _is_ set, puts the heap on hugepages, but leaves a gap in the heap. 3. /sys/kernel/mm/transparent_hugepage/enabled = always. HUGETLB_MORECORE=thp may or may not add some value. The heap ought to end up on hugepages even without libhugetlbfs as long as the heap is large enough. HUGETLB_MORECORE=thp may result in small heaps ending up on hugepages, but unfortunately it puts a gap in the heap. My opinion: There's no reason for HUGETLB_MORECORE=thp to _not_ do the madvise. HUGETLB_MORECORE=thp should be implemented as a wrapper around sbrk; it should _not_ add a gap to the heap. Regards, -Andrew Hastings Cray Inc. ------------------------------------------------------------------------------ EditLive Enterprise is the world's most technically advanced content authoring tool. Experience the power of Track Changes, Inline Image Editing and ensure content is compliant with Accessibility Checking. http://p.sf.net/sfu/ephox-dev2dev _______________________________________________ Libhugetlbfs-devel mailing list Libhugetlbfs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/libhugetlbfs-devel
