On 12/15/2017 06:58 AM, 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. Right, thats as per design. > > 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 That is the async method by analyzing page table segment for the process by khugepaged and evaluate if a huge page can be installed replacing the existing pages. > translation performance and memory consumption. Currently there > is no way for an application to choose this compromise for the > page fault conditions above. Cant we mark the THP enablement mode as "madvise", then switch between MADV_HUGEPAGE/MADV_NOHUGEPAGE to implement this ? > > With this change, when an application issues MADV_DONTNEED on a > memory region, the region is marked as "space-efficient". For Isn't it that MADV_DONTNEED should be used for a region where there are already pages faulted in and page table populated ? Are you suggesting that MADV_DONTNEED should be called upon a region just after creation to control it's fault behavior ? Thats not what MADV_DONTNEED was meant to be. > 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 But MADV_HUGEPAGE/MADV_NOHUGEPAGE combination should do the trick as well. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
