Date: Fri, 7 Feb 2003 20:16:59 -0800 From: Alfred Perlstein <bright@mu.org> To: Jeff Roberson <jroberson@chesapeake.net> Cc: arch@FreeBSD.ORG Subject: Re: New kernel allocation API Message-ID: <20030208041659.GC88781@elvis.mu.org> In-Reply-To: <20030207221623.V72073-100000@mail.chesapeake.net> References: <20030208022722.GB88781@elvis.mu.org> <20030207221623.V72073-100000@mail.chesapeake.net>
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* Jeff Roberson <jroberson@chesapeake.net> [030207 19:17] wrote: > > > On Fri, 7 Feb 2003, Alfred Perlstein wrote: > > > *snip* > > > > It seems that you've missed reading the original allocator or something, > > there's a cheap way to do this that doesn't require too much overhead. > > It seems that you've missed reading my email. > > "The old code used a large fixed size array that represented all of > kmem_map. This no longer works because the allocator can return pages > that are outside of kmem map. It does this on alpha, ia64, and sparc64 to > use direct mapped regions of address space for kernel memory." > > > Yes there is a space tradeoff, but it avoids this pmap_kextract > > nonsense and multiple pointer dereferences. > > It's not so much nonsense as it is a solution. Doh, I guess I should be paying more attention, sorry for that. What advantage do you get from using direct mapped pages? Why not alias/map them into kmem map? I know you'd pay a penalty for the vm overhead, but you'd gain back the fixed array trick. I'm probably missing something? -- -Alfred Perlstein [alfred@freebsd.org] 'Instead of asking why a piece of software is using "1970s technology," start asking why software is ignoring 30 years of accumulated wisdom.' To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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