linux-kernel - Re: [patch 00/41] cpu alloc / cpu ops v3: Optimize per cpu access

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]

Message-Id: <20080529231618.56e4028b.akpm@linux-foundation.org>
Date:	Thu, 29 May 2008 23:16:18 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	Christoph Lameter <clameter@....com>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, David Miller <davem@...emloft.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Mike Travis <travis@....com>
Subject: Re: [patch 00/41] cpu alloc / cpu ops v3: Optimize per cpu access

On Fri, 30 May 2008 08:01:02 +0200 Eric Dumazet <dada1@...mosbay.com> wrote:

> Really, percpu allocations are currently not frequent at all.
> 
> vmalloc()/vfreee() are way more frequent and still use a list.

Sure it's hard to conceive how anyone could go and do a per-cpu
allocation on a fastpath.

But this has nothing to do with the frequency!  The problems surround
the _amount_ of allocated memory and the allocation/freeing patterns.

Here's another example.  And it's only an example!  Generalise!

ext3 maintains three percpu_counters per mount.  Each percpu_counter
does one percpu_alloc.  People can mount an arbitrary number of ext3
filesystems!

Another: there are two percpu_counters (and hence two percpu_alloc()s)
per backing_dev_info.  One backing_dev_info per disk and people have
been known to have thousands (iirc ~10,000) disks online.

And those examples were plucked only from today's kernel.  Who knows
what other problems will be in 2.6.45?
--
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/