Date: Fri, 20 Feb 2015 15:14:28 -0500 From: John Baldwin <jhb@freebsd.org> To: "K. Macy" <kmacy@freebsd.org> Cc: Alan Cox <alc@freebsd.org>, Adrian Chadd <adrian@freebsd.org>, Konstantin Belousov <kib@freebsd.org>, John-Mark Gurney <jmg@funkthat.com>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: getting NUMA into the tree (userland most interesting for me) Message-ID: <2069208.rjIe3PXOHb@ralph.baldwin.cx> In-Reply-To: <CAHM0Q_Po7zkXhsS6N75sbLY1b5GmHmKbBE7T4z6dQg3CGWAuYw@mail.gmail.com> References: <20150219041012.GJ1953@funkthat.com> <CAJ-Vmok4peyq95o7%2BT7EkEEVb2ZqU3Y0pd_9kTMyBrxuhvX05w@mail.gmail.com> <CAHM0Q_Po7zkXhsS6N75sbLY1b5GmHmKbBE7T4z6dQg3CGWAuYw@mail.gmail.com>
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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. -- John Baldwin
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