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Date: Mon, 07 Apr 2008 17:36:59 +0200 From: Eric Dumazet <dada1@...mosbay.com> To: Andi Kleen <andi@...stfloor.org> Cc: Robert Olsson <Robert.Olsson@...a.slu.se>, Stephen Hemminger <shemminger@...tta.com>, David Miller <davem@...emloft.net>, netdev@...r.kernel.org Subject: Re: [RFC] fib_trie: memory waste solutions Andi Kleen a écrit : > On Mon, Apr 07, 2008 at 04:42:35PM +0200, Robert Olsson wrote: > >> Andi Kleen writes: >> >> > > Do we get slower with vmalloc due to TLB-lookups etc? Guess this >> > > should be investigated. >> > >> > In some cases it might even go faster because a lot of x86 CPUs >> > have far more 4K TLBs than 2M TLBs. vmalloc is just quite expensive >> > in setup/free time, but that shouldn't be a big issue here. >> >> >> I've did some rDoS testing and the lookup performance is the same or >> slightly better. So it should be fine. >> > > If you want more realistic worst case numbers run something in user space in > the background that thrashes the TLBs constantly and then see how > the numbers change. > > The main advantage of using large pages is that they tend to be separated > from 4K TLBs and since most user space doesn't use large pages it > gives the kernel an effective private TLB pool. > > With vmalloc it will now compete with whatever other TLB pigs are active. > Yes, but with vmalloc(), NUMA machines have some chance to distribute this big area on several nodes (only if the process currently expanding the fib_trie root node has an appropriate numa_policy.... ah well :) :) ) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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