linux-kernel - Re: [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges

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]

Date:	Fri, 29 Feb 2008 22:23:27 +0100
From:	Andrea Arcangeli <andrea@...ranet.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>, akpm@...ux-foundation.org,
	Robin Holt <holt@....com>, Avi Kivity <avi@...ranet.com>,
	Izik Eidus <izike@...ranet.com>,
	kvm-devel@...ts.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	general@...ts.openfabrics.org,
	Steve Wise <swise@...ngridcomputing.com>,
	Roland Dreier <rdreier@...co.com>,
	Kanoj Sarcar <kanojsarcar@...oo.com>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com
Subject: Re: [patch 2/6] mmu_notifier: Callbacks to invalidate address
	ranges

On Fri, Feb 29, 2008 at 01:03:16PM -0800, Christoph Lameter wrote:
> That means we need both the anon_vma locks and the i_mmap_lock to become 
> semaphores. I think semaphores are better than mutexes. Rik and Lee saw 
> some performance improvements because list can be traversed in parallel 
> when the anon_vma lock is switched to be a rw lock.

The improvement was with a rw spinlock IIRC, so I don't see how it's
related to this.

Perhaps the rwlock spinlock can be changed to a rw semaphore without
measurable overscheduling in the fast path. However theoretically
speaking the rw_lock spinlock is more efficient than a rw semaphore in
case of a little contention during the page fault fast path because
the critical section is just a list_add so it'd be overkill to
schedule while waiting. That's why currently it's a spinlock (or rw
spinlock).

> Sounds like we get to a conceptually clean version here?

I don't have a strong opinion if it should become a semaphore
unconditionally or only with a CONFIG_XPMEM=y. But keep in mind
preempt-rt runs quite a bit slower, or we could rip spinlocks out of
the kernel in the first place ;)
--
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/