On Thu 18-01-18 15:33:16, Nitin Gupta wrote: > From: Nitin Gupta <nitin.m.gupta@xxxxxxxxxx> > > 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. Yes, this is true but hardly unexpected for MADV_HUGEPAGE or THP always users. > 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. Is that really true? We have /sys/kernel/mm/transparent_hugepage/khugepaged/max_ptes_none This is not reflected during the PF of course but you can control the behavior there as well. Either by the global setting or a per proces prctl. > With this change, whenever 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. Kirill didn't like it in the previous version and I do not like this either. You are adding a very subtle side effect which might completely unexpected. Consider userspace memory allocator which uses MADV_DONTNEED to free up unused memory. Now you have put it out of THP usage basically. If the memory is used really scarce then we have MADV_NOHUGEPAGE. -- Michal Hocko SUSE Labs -- 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>
