Date: Thu, 20 Nov 2014 11:18:55 -0500 From: John Baldwin <jhb@freebsd.org> To: freebsd-hackers@freebsd.org Cc: Sebastian Kuzminsky <S.Kuzminsky@f5.com> Subject: Re: 1 gig superpages Message-ID: <201411201118.56050.jhb@freebsd.org> In-Reply-To: <D0862E49.6051%seb@f5.com> References: <D0862E49.6051%seb@f5.com>
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On Monday, November 10, 2014 11:15:09 am Sebastian Kuzminsky wrote: > Hello hackers, I'm announcing the availability of a branch adding support for 1 GB superpages to FreeBSD. > > https://github.com/Seb-LineRate/freebsd/commits/seb/stable-10/1-gig-pages > > The branch is based on work done by Line Rate Systems and F5 Networks, and used in our LROS load-balancing product. > > Our product is based on FreeBSD 9.1; the branch I linked to above is our 1 gig page support rebased onto stable/10. I probably messed something up in the rebase, as lots of things changed both in pmap and vm since 9.1. There are also a handful of commits that i haven't gotten to yet, but they are less consequential - just performance improvements to the buddy allocator. I hope to push those over the next few days. > > It should be relatively easy to rebase the branch onto Current. > > > This is a work in progress, and I would appreciate feedback and comments. So my initial thoughts from having looked at this very briefly is that this is a bit hackish. In particular, the reservation system already supports multiple levels of reservations so that you could have a separate reservation layer for 1GB pages. However, that alone doesn't get you exactly what you want, which is that you want to guarantee a specific page size. This is also something that would be nice to have for 2MB pages as well, and I have talked a bit about that with Alan in the past. What I do think would be useful would be to have a new mmap flag which requests that a mapping not use demotion/promotion but fully use any reservations it makes. You could also have it fail if it can't get reservations for the entire range. Alan suggests to call this MAP_HUGETLB to match Linux since it would provide similar semantics. If you then add 1GB pages as an second reservation level on amd64 and make the semantics of MAP_HUGETLB such that it uses the largest reservations possible for the mapping size (so a request for 1G uses 1G page instead of 2M pages), then that would give you what you want without having various 1G-specific functions scattered in MI code, etc. It will also be more useful for other platforms going forward (some of which support multiple page sizes that aren't just the 'trim a tree layer' PSE-style you have on x86). -- John Baldwin
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