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Date: Tue, 05 Jan 2010 09:18:16 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>, Minchan Kim <minchan.kim@...il.com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, cl@...ux-foundation.org, "hugh.dickins" <hugh.dickins@...cali.co.uk>, Nick Piggin <nickpiggin@...oo.com.au>, Ingo Molnar <mingo@...e.hu> Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault() On Mon, 2010-01-04 at 21:10 -0800, Linus Torvalds wrote: > Sounds doable. But it also sounds way more expensive than the current VM > fault handling, which is pretty close to optimal for single-threaded > cases.. That RCU lookup might be cheap, but just the refcount is generally > going to be as expensive as a lock. Right, that refcount adds two atomic ops, the only grace it has is that its in the vma as opposed to the mm, but there are plenty workloads that concentrate on a single vma, in which case you get an equally contended cacheline as with the mmap_sem. I was trying to avoid having to have that refcount, but then sorta forgot about the actual fault handlers also poking at the vma :/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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