linux-kernel - Re: [patch] generic rwsems

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Message-ID: <25428.1176464690@redhat.com>
Date:	Fri, 13 Apr 2007 12:44:50 +0100
From:	David Howells <dhowells@...hat.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	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 

Nick Piggin <npiggin@...e.de> wrote:

> I think I should put wait_lock after wait_list, so as to get a better
> packing on most 64-bit architectures.

It makes no difference.  struct lockdep_map contains at least one pointer and
so is going to be 8-byte aligned (assuming it's there at all).  struct
rw_semaphore contains at least one pointer/long, so it will be padded out to
8-byte size.

If you want to make a difference, you'd need to add __attribute__((packed))
but you would need to be very careful with that.

David
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