Date: Mon, 18 Aug 2014 14:52:12 -0500 From: Alan Cox <alan.l.cox@gmail.com> To: Adrian Chadd <adrian@freebsd.org> Cc: Konstantin Belousov <kostikbel@gmail.com>, "freebsd-arch@freebsd.org" <arch@freebsd.org>, Gleb Smirnoff <glebius@freebsd.org>, "Alexander V. Chernikov" <melifaro@freebsd.org>, "Andrey V. Elsukov" <ae@freebsd.org> Subject: Re: superpages for UMA Message-ID: <CAJUyCcOSoFwHmeX=fN3deqAZPn-T3EFtCkFje5u8woDz2qoaRw@mail.gmail.com> In-Reply-To: <CAJ-VmokXDtXSqCKo9wNVeqd9yQeZwgvjWqPA4tQnydx%2B0W_Gzg@mail.gmail.com> References: <53F215A9.8010708@FreeBSD.org> <20140818183925.GP2737@kib.kiev.ua> <CAJ-VmokXDtXSqCKo9wNVeqd9yQeZwgvjWqPA4tQnydx%2B0W_Gzg@mail.gmail.com>
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On Mon, Aug 18, 2014 at 2:45 PM, Adrian Chadd <adrian@freebsd.org> wrote: > Hi! > > I dug into this a little bit last year. I saw a lot of time spent just > walking TLBs for VM pages when doing a lot of VM page -> network > pushing. > > On the sandy bridge boxes with 1G page entries, the TLB only has 4 entries. > > The high area of memory isn't 1G aligned, so we don't use 1G pages for > all the stuff that's allocated initially. That includes, among other > things, all the VM memory that you need. > > The other thing that crept up was that we don't try to reserve memory > in any way - we'll just fragment stuff quickly from the pmap and > allocate where we can when we can. So there's currently no attempt to > allocate small kernel structures from the same underlying 1G page. > > For uma_small_alloc(), there is VM_FREEPOOL_DIRECT. However, this is still tuned for 2 MB pages. > That'd be an interesting experiment - allocating VM entries and other > small things like rtentry and mbuf UMA entries from one or two 1GB > regions of memory. It may make better use of the 1G (or 2M) TLB > entries and keep things hot. > > > > -a > _______________________________________________ > freebsd-arch@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-arch > To unsubscribe, send any mail to "freebsd-arch-unsubscribe@freebsd.org" >
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