linux-kernel - Re: [RFC][PATCH 6/8] mm: handle_speculative

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1262679496.2400.14.camel@laptop>
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/