Messages in this thread | | | Date | Sat, 13 May 2023 13:10:56 -0700 | From | Davidlohr Bueso <> | Subject | Re: Futexes & Folios |
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On Sat, 13 May 2023, Matthew Wilcox wrote:
>Here's a patch which converts the futex code from using pages to using >folios. I do have some questions. > > - I assume we really do want to base the key on the page offset of the > futex in the file. That is, it's not good enough to base the key > on the folio's index because the folio can be split after setting up > the key, and if it is we'd then fail to find the futex later. > - In hugetlbfs, it doesn't matter whether the pgoff is based on base > pages or huge page size -- as long as it's consistent between > invocations, everything will work
As tglx already mentioned, yes to both.
>(I have ideas about a get_user_folio() but those are not represented in >this patch)
Btw, regarding some of the concerns about the gup overhead for futexes in the physr discussion at lsfmm; 'perf bench futex hash' would be a good way of measuring any impact at a micro level and going from there. This is only necessary of course for shared futexes, fast/private ones just use the address space.
Thanks, Davidlohr
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