linux-kernel - Re: [patch 3/9] Guest page hinting: volatile page cache.

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]

Date:	Fri, 01 Sep 2006 09:29:17 -0700
From:	Dave Hansen <haveblue@...ibm.com>
To:	schwidefsky@...ibm.com
Cc:	Andy Whitcroft <apw@...dowen.org>, linux-kernel@...r.kernel.org,
	virtualization@...ts.osdl.org, akpm@...l.org,
	nickpiggin@...oo.com.au, frankeh@...son.ibm.com
Subject: Re: [patch 3/9] Guest page hinting: volatile page cache.

On Fri, 2006-09-01 at 18:04 +0200, Martin Schwidefsky wrote:
> 3) The page-has-a-writable-mapping (PG_writable) bit is set when the
> first writable pte for a page is established. The page needs to have a
> different state if a writable pte exists compared to a read-only page.
> The alternative without the page bit would be to do the state change
> every time a writable pte is established or to search all ptes of a
> given page. Both have performance implications.  

What are the performance implications?  Do they completely erase any
performance gains that these patches might have given in the first
place?  Has there been any evaluation of these other two alternatives?
As I understand it, carrying out this performance analysis would be very
difficult for most of the kernel community to perform.

Keeping a nice count of the number of writable PTEs sounds like
something that might be generally useful.  Could we split
page->_mapcount to keep track of r/o and r/w ptes separately?  Or,
perhaps a single bit in it can be utilized to replace PG_writable,
instead.

-- Dave

-
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/