Date: Wed, 22 Jan 2014 23:32:51 -0800 From: Adrian Chadd <adrian@freebsd.org> To: Garrett Wollman <wollman@freebsd.org> Cc: Navdeep Parhar <np@freebsd.org>, "net@freebsd.org" <net@freebsd.org> Subject: Re: Use of contiguous physical memory in cxgbe driver Message-ID: <CAJ-VmokL2nXX-cAOsXmW3YjiHmU86JfTco7P=Gcx2SFHNrGwSQ@mail.gmail.com> In-Reply-To: <21216.36928.132606.318491@hergotha.csail.mit.edu> References: <21216.22944.314697.179039@hergotha.csail.mit.edu> <52E06104.70600@FreeBSD.org> <21216.36928.132606.318491@hergotha.csail.mit.edu>
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It's about time we taught the physmem allocator to be more conducive to physically contiguous allocations. A server with gigabytes of memory should be able to keep a couple tens of megabytes of 64k sized allocation chunks around for exactly this. -a On 22 January 2014 19:45, Garrett Wollman <wollman@freebsd.org> wrote: > <<On Wed, 22 Jan 2014 16:23:32 -0800, Navdeep Parhar <np@FreeBSD.org> said: > >> On 01/22/14 15:52, Garrett Wollman wrote: >>> At this point everyone is well aware that requiring contiguous >>> physical page when the hardware can do scatter-gather is a very bad >>> idea. > >> I wouldn't put it this way. Using buffers with size > PAGE_SIZE has its >> advantages. > > These advantages do not come close to balancing out the disadvantage > of "your server eventually falls off the network due to physmem > fragmentation, better hope you can reset it remotely because driving > in to work at 3 AM sucks." > > If any free pages are available at all, the allocation of a 4k jumbo > mbuf will succeed. A 9k jumbo mbuf requires three physically > contiguous pages, and it's very, very easy for physical memory to get > fragmented to the point where that is impossible. > > -GAWollman > > _______________________________________________ > freebsd-net@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org"
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