Date: Sat, 23 Jul 2005 12:12:24 -0700 From: Peter Wemm <peter@wemm.org> To: Petri Helenius <pete@he.iki.fi> Cc: freebsd-amd64@freebsd.org Subject: Re: kernel memory Message-ID: <200507231212.24708.peter@wemm.org> In-Reply-To: <42DFF043.3090203@he.iki.fi> References: <42DFDCCA.8050207@he.iki.fi> <200507210137.29816.peter@wemm.org> <42DFF043.3090203@he.iki.fi>
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On Thursday 21 July 2005 11:58 am, Petri Helenius wrote: > Peter Wemm wrote: > >2GB for paged kernel memory. But in addition we access memory via > > the direct map area to avoid the need for temporary mappings in > > many cases. uma (malloc, mbufs) etc use this, as does the sfbuf > > temporary mapping system. > > So there is no limitation for malloced memory? Say if my driver would > like to have 4 or 8 gig lookup cache that would work? AARGH. I've just found a bug/feature in the memory allocator. There are two code paths, one for small (<PAGE_SIZE) allocations, which uses the direct map allocations instead of kvm allocations, and the other large chunk allocator that simply allocates pages at a time from kvm. :-( I suspect this is because malloc's semantics depend on objects being contiguous. The direct map method would allocate physically discontiguous pages. So, if you allocated your lookup cache in <4K chunks, you could have as much as you like. :-/ -- Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com "All of this is for nothing if we don't go to the stars" - JMS/B5
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