Date: Fri, 20 Feb 2015 16:37:12 -0600 From: Alan Cox <alc@rice.edu> To: John Baldwin <jhb@freebsd.org> Cc: Adrian Chadd <adrian@freebsd.org>, "K. Macy" <kmacy@freebsd.org>, Alan Cox <alc@freebsd.org>, John-Mark Gurney <jmg@funkthat.com>, Konstantin Belousov <kib@freebsd.org>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: getting NUMA into the tree (userland most interesting for me) Message-ID: <968C1AD7-D806-4E69-87E4-AB88A4C5AA70@rice.edu> In-Reply-To: <2069208.rjIe3PXOHb@ralph.baldwin.cx> References: <20150219041012.GJ1953@funkthat.com> <CAJ-Vmok4peyq95o7%2BT7EkEEVb2ZqU3Y0pd_9kTMyBrxuhvX05w@mail.gmail.com> <CAHM0Q_Po7zkXhsS6N75sbLY1b5GmHmKbBE7T4z6dQg3CGWAuYw@mail.gmail.com> <2069208.rjIe3PXOHb@ralph.baldwin.cx>
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On Feb 20, 2015, at 2:14 PM, John Baldwin <jhb@freebsd.org> wrote: > On Friday, February 20, 2015 12:17:09 AM K. Macy wrote: >>>>> Yes, I think we have a fair bit to do in the kernel before we are in a >>>>> position to export anything truly useful to userland unfortunately. The >>>>> last time I talked with Jeff about projects/numa (after the first draft >>>>> of the wiki page) I came away with the impression that there might be >>>>> some things we can pull out of that branch, but that it isn't suitable >>>>> for merging upstream directly. Jeff noted that he and Alan had gone >>>>> through several iterations of this already (I believe at least 3 >>>>> completely different policy designs) all of which had their own issues. >>>>> >>>>> Outside of the VM I think that we can keep the APIs somewhat stable by >>>>> having this opaque policy cookie to pass around that we can redefine >>>>> the guts of later. However, various parts of the VM all have to handle >>>>> whatever the policy defines, and while the vm_phys bits and >>>>> contigmalloc() might be kind of obvious to implement, higher level VM >>>>> layers like kmem() and malloc() are more complicated. One thing that >>>>> is in projects/numa is changes for UMA that we can hopefully reuse much >>>>> of, but I don't recall how much (if any) of kmem/malloc is in there. >>>>> Also, while vm_phys is one of the first things to do, I know that Alan >>>>> and Jeff have pending patches to remove the cache queue (since it is >>>>> far less useful than it seems) which simplify vm_phys making it easier >>>>> to implement NUMA policies there, so I'm hoping we can get that in >>>>> sooner before having to start tearing up the VM too much. This is why >>>>> the stuff I currently have is targeted non-VM bits like interrupts as >>>>> getting that correct is lower-hanging fruit that might provide some >>>>> gains regardless. Even once vm_phys is done I think the first thing to >>>>> tackle next is contigmalloc to facilitate static bus_dma allocations >>>>> (descriptor rings and such) being local to a device. >>>> >>>> Contigmalloc improvements and cache queue removal are in the >>>> phabricator queue now. They are also prerequisites for per-cpu free >>>> page caches which are a huge scalability improvement for some >>>> workloads such as Netflix's. >>>> >>>> There is still a fair amount of scalability work (including Jeffr's >>>> per-domain pagedaemon work) that really needs to happens before we can >>>> seriously think about a general user-level NUMA interface. >>> >>> Is there anything wrong with maybe bringing over the basic low level >>> allocator changes from projects/numa so the basics are there? >> >> I think they're probably predicated on the work that is being >> shepherded in now. Even if not, it would require someone to shepherd >> it in and the corresponding spare cycles from alc to review / revise / >> repeat - which seem to be in short supply. > > Can you add entries for these to the wiki page with links to the phab reviews? > I know there is an entry for the page cache queue removal already, but you > could add one for contigmalloc right next to it. > Essentially, the “Remove the ‘cache’ page queue” task has a number of significant subtasks that aren’t listed, and the contigmalloc() rewrite is the biggest of them. Specifically, the current contigmalloc(M_WAITOK) implementation exploits the existence of the ‘cache’ page queue, and to eliminate that dependence requires the M_WAITOK case to work very differently.help
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