linux-kernel - Re: Non-linear Remap Vs. VM Cleanup: Performance Hit

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] [day] [month] [year] [list]

Date:	Fri, 27 Feb 2015 17:39:05 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	"D. Cooper Stevenson" <cooper@...per.stevenson.name>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Non-linear Remap Vs. VM Cleanup: Performance Hit

On Tue, Feb 24, 2015 at 02:36:25PM -0800, D. Cooper Stevenson wrote:
> Hello All,
> 
> I read the Linus's release for RC1. One of his favorite features in the
> release are, "actually some vm cleanups, where this release is getting rid
> of the largely unused non-linear remapping code (replaced with just
> emulating it with lots of smaller mappings) and unifies the NUMA and
> PROTNONE handling for page tables."
> 
> I understand that non-linear page remapping is unused (and, presumably,
> reduces the code base size) but according to the remap_file_pages man page
> (http://man7.org/linux/man-pages/man2/remap_file_pages.2.html) non-linear
> system will be, "eventually be replaced by a slower in-kernel emulation."
> 
> Was this a change of necessity? What gives?

As with all cleanups it's not necessary, but it makes life easier.

It removed >1.5k lines of non-trivial code from critical path of the
kernel. It's rarely used and tend to be error-prone. And developers need
to be aware about exists of non-linear mapping while implementing new
features.

For instance, faultaround feature I've implemented was broken for
non-linear mapping for some time and it took time to track it down.

-- 
 Kirill A. Shutemov
--
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/