linux-kernel - Re: [PATCH 0/2] pdflush fix and enhancement

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:	Thu, 1 Jan 2009 02:48:26 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	"Peter W. Morreale" <pmorreale@...ell.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] pdflush fix and enhancement

On Wed, Dec 31, 2008 at 09:08:26AM -0700, Peter W. Morreale wrote:
> On Wed, 2008-12-31 at 14:27 +0100, Andi Kleen wrote:
> > > I say most because the assumption would be that we will be successful in
> > > creating the new thread.  Not that bad an assumption I think.  Besides,
> > 
> > And that the memory read is not reordered (rmb()).
> > 
> 
> At the risk of showing my b*tt here...  I'm not very clear on memory
> barriers, is this necessary even inside a critical region?  (recall
> we're protected by the spin lock).

You're right the implied barriers in the spinlock are probably enough.
Never mind.

> If so, does the barrier go after the
> read, or before?   (Thanks for not laughing, however grins are allowed)

Before.

BTW on x86 it's a nop either way, but not on all other architectures.

> 
> 
> > 
> > Ok it probably needs some kind of feedback mechanism.
> > 
> 
> Actually, I tend to think we need an entirely different approach to
> flushing, please see my post to David Chinner which outlines some
> thoughts.  Basically a flushing heuristic that takes into account the
> characteristics of the various block devices.  

Ideally discovered at runtime (e.g. by watching queue lengths/service
times etc.) though. Otherwise the kernel would need to have knowledge
about the properties of all kinds of devices.

-Andi
-- 
ak@...ux.intel.com
--
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/