linux-kernel - Re: [rfc 08/45] cpu alloc: x86 support

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:	Mon, 19 Nov 2007 17:35:06 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Christoph Lameter <clameter@....com>
CC:	ak@...e.de, akpm@...ux-foundation.org, travis@....com,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	linux-kernel@...r.kernel.org
Subject: Re: [rfc 08/45] cpu alloc: x86 support

Christoph Lameter wrote:
> 
> For the UP and SMP case map the area using 4k ptes. Typical use of per cpu
> data is around 16k for UP and SMP configurations. It goes up to 45k when the
> per cpu area is managed by cpu_alloc (see special x86_64 patchset).
> Allocating in 2M segments would be overkill.
> 
> For NUMA map the area using 2M PMDs. A large NUMA system may use
> lots of cpu data for the page allocator data alone. We typically
> have large amounts of memory around on those size. Using a 2M page size
> reduces TLB pressure for that case.
> 
> Some numbers for envisioned maximum configurations of NUMA systems:
> 
> 4k cpu configurations with 1k nodes:
> 
> 	4096 * 16MB = 64TB of virtual space.
> 
> Maximum theoretical configuration 16384 processors 1k nodes:
> 
> 	16384 * 16MB = 256TB of virtual space.
> 
> Both fit within the established limits established.
> 

You're making the assumption here that NUMA = large number of CPUs. 
This assumption is flat-out wrong.

On x86-64, most two-socket systems are still NUMA, and I would expect 
that most distro kernels probably compile in NUMA.  However,
burning megabytes of memory on a two-socket dual-core system when we're 
talking about tens of kilobytes used would be more than a wee bit insane.

I do like the concept, overall, but the above distinction needs to be fixed.

	-hpa
-
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/