linux-kernel - Re: #tj-percpu has been rebased

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 for Android: free password hash cracker in your pocket

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

Message-ID: <4999F693.5000105@zytor.com>
Date:	Mon, 16 Feb 2009 15:28:19 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>, cpw@....com
Subject: Re: #tj-percpu has been rebased

Rusty Russell wrote:
>>
>> All in all I think a dedicated virtual zone per CPU as opposed to
>> interleaving them seems to make more sense.  Even with 4096 CPUs and
>> reserving, say, 256 MB per CPU it's not that much address space in the
>> context of a 47-bit kernel space.  On 32 bits I don't think anything but
>> the most trivial amount of percpu space is going to fly no matter what.
> 
> It's the TLB cost which I really don't want to pay; num_possible_cpus()
> 4096 non-NUMA is a little silly (currently impossible).
> 
> I'm happy to limit per-cpu allocations to pagesize, then you only need to
> find num_possible_cpus() contig pages, and if you can't, you fall back to
> vmalloc.
> 

num_possible_cpus() can be very large though, so in many cases the
likelihood of finding that many pages approach zero.  Furthermore,
num_possible_cpus() may be quite a bit larger than the actual number of
CPUs in the system.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

--
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/