linux-kernel - Re: [QUICKLIST 0/4] Arch independent quicklists V2

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:	Tue, 13 Mar 2007 04:15:51 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	clameter@....com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [QUICKLIST 0/4] Arch independent quicklists V2

> On Tue, 13 Mar 2007 22:06:46 +1100 Nick Piggin <nickpiggin@...oo.com.au> wrote:
> Andrew Morton wrote:
> >>On Tue, 13 Mar 2007 19:03:38 +1100 Nick Piggin <nickpiggin@...oo.com.au> wrote:
> 
> ...
>
> >>Page allocator still requires interrupts to be disabled, which this doesn't.

> >>it is worthwhile.
> > 
> > 
> > If you want a zeroed page for pagecache and someone has just stuffed a
> > known-zero, cache-hot page into the pagetable quicklists, you have good
> > reason to be upset.
> 
> The thing is, pagetable pages are the one really good exception to the
> rule that we should keep cache hot and initialise-on-demand. They
> typically are fairly sparsely populated and sparsely accessed. Even
> for last level page tables, I think it is reasonable to assume they will
> usually be pretty cold.

eh?  I'd have thought that a pte page which has just gone through
zap_pte_range() will very often have a _lot_ of hot cachelines, and
that's a common case.

Still.   It's pretty easy to test.

> > 
> > Maybe, dunno.  It was apparently a win on powerpc many years ago.  I had a
> > fiddle with it 5-6 years ago on x86 using a cache-disabled mapping of the
> > page.  But it needed too much support in core VM to bother.  Since then
> > we've grown per-cpu page magazines and __GFP_ZERO.  Plus I'm not aware of
> > anyone having tried doing it on x86 with non-temporal stores.
> 
> You can win on specifically constructed benchmarks, easily.
> 
> But considering all the other problems you're going to introduce, we'd need
> a significant win on a significant something, IMO.
> 
> You waste memory bandwidth. You also use more CPU and memory cycles
> speculatively, ergo you waste more power.

Yeah, prezeroing in idle is probably pointless.  But I'm not aware of
anyone having tried it properly...
-
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/