linux-kernel - Re: [patch] generic rwsems

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: <20070413162909.c436a732.dada1@cosmosbay.com>
Date:	Fri, 13 Apr 2007 16:29:09 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	David Howells <dhowells@...hat.com>
Cc:	Nick Piggin <npiggin@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch] generic rwsems

On Fri, 13 Apr 2007 14:31:52 +0100
David Howells <dhowells@...hat.com> wrote:

> Break the counter down like this:
> 
> 	0x00000000	- not locked; queue empty
> 	0x40000000	- locked by writer; queue empty
> 	0xc0000000	- locket by writer; queue occupied
> 	0x0nnnnnnn	- n readers; queue empty
> 	0x8nnnnnnn	- n readers; queue occupied

If space considerations are that important, we could then reserve one bit for the 'wait_lock spinlock'

0x20000000 : one cpu gained control of 'wait_list'

This would save 4 bytes on 32 bit platforms.

64 bit platforms could have a limit of 2^60 threads, instead of the way too small 2^28 one ;)

(we loose the debug version of spinlock of course)

Another possibility to save space would be to move wait_lock/wait_list outside of rw_semaphore, in a hashed global array.
This would save 12/16 bytes per rw_semaphore (inode structs are probably the most demanding)
-
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/