linux-kernel - Re: [RFC][PATCH 1/6] count transparent hugepage splits

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: <20110204211825.GJ30909@random.random>
Date:	Fri, 4 Feb 2011 22:18:25 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Dave Hansen <dave@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Michael J Wolf <mjwolf@...ibm.com>
Subject: Re: [RFC][PATCH 1/6] count transparent hugepage splits

On Thu, Feb 03, 2011 at 01:22:14PM -0800, David Rientjes wrote:
> i.e. no global locking, but we've accepted the occassional off-by-one 
> error (even though splitting of hugepages isn't by any means lightning 
> fast and the overhead of atomic ops would be negligible).

Agreed losing an increment is not a problem, but in very large systems
it will become a bottleneck. It's not super urgent, but I think it
needs to become a per-cpu counter sooner than later (not needed
immediately but I would appreciate an incremental patch soon to
address that). split_huge_page is already fully SMP scalable if the
rmap isn't shared (i.e. fully SMP scalable across different execve)
and I'd like it to stay that way because split_huge_page can run at
high frequency at times from different processes, so in very large
systems it may be measurable, with that cacheline bouncing around 1024
cpus. pages_collapsed is not a problem because it's only used by one
kernel thread so it can't be contended. Again not super urgent but
better to optimize it ;).
--
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/