On Thu, Dec 14, 2017 at 05:28:52PM -0800, Nitin Gupta wrote: > Currently, if the THP enabled policy is "always", or the mode > is "madvise" and a region is marked as MADV_HUGEPAGE, a hugepage > is allocated on a page fault if the pud or pmd is empty. This > yields the best VA translation performance, but increases memory > consumption if some small page ranges within the huge page are > never accessed. > > An alternate behavior for such page faults is to install a > hugepage only when a region is actually found to be (almost) > fully mapped and active. This is a compromise between > translation performance and memory consumption. Currently there > is no way for an application to choose this compromise for the > page fault conditions above. > > With this change, when an application issues MADV_DONTNEED on a > memory region, the region is marked as "space-efficient". For > such regions, a hugepage is not immediately allocated on first > write. Instead, it is left to the khugepaged thread to do > delayed hugepage promotion depending on whether the region is > actually mapped and active. When application issues > MADV_HUGEPAGE, the region is marked again as non-space-efficient > wherein hugepage is allocated on first touch.
I think this would be NAK. At least in this form. What performance testing have you done? Any numbers? Making whole vma "space_efficient" just because somebody freed one page from it is just wrong. And there's no way back after this. > > Orabug: 26910556 Wat? -- Kirill A. Shutemov
