Messages in this thread | | | Date | Wed, 22 Jan 2014 13:46:04 -0800 (PST) | From | David Rientjes <> | Subject | Re: [RFC PATCH] mm: thp: Add per-mm_struct flag to control THP |
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On Wed, 22 Jan 2014, Alex Thorlton wrote:
> > I would expect that the alternative solution to a per-mm switch is to > > reserve the naturally aligned pages for a THP promotion. Have a threshold > > of pages pages that must be faulted before the full THP's worth of pages > > is allocated, zero'd and a huge pmd established. That would defer the > > THP setup costs until it was detected that it was necessary. > > I have some half-finished patches that I was working on a month or so > ago, to do exactly this (I think you were involved with some of the > discussion, maybe? I'd have to dig up the e-mails to be sure). After > cycling through numerous other methods of handling this problem, I still > like that idea, but I think it's going to require a decent amount of > effort to get finished. >
If you're going to go this route, I think a sane value would be max_ptes_none that controls when khugepaged would re-collapse a split hugepage into another hugepage after something does madvise(MADV_DONTNEED) to a region, for example. Otherwise it could collapse that memory into a hugepage even though it wasn't faulted as huge.
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