linux-kernel - Re: [PATCH 1/8] Scaling msgmni to the amount of lowmem

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Date:	Tue, 20 May 2008 16:45:55 +0200
From:	Nadia Derbey <Nadia.Derbey@...l.net>
To:	Michael Kerrisk <mtk.manpages@...glemail.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm@...r.kernel.org
Subject: Re: [PATCH 1/8] Scaling msgmni to the amount of lowmem

Michael Kerrisk wrote:
> Hello Nadia,
> 
> Regarding your:
> 
> [PATCH 1/8] Scaling msgmni to the amount of lowmem
> http://article.gmane.org/gmane.linux.kernel/637849/
> which I see has made its way in 2.6.26-rc
> 
> Your patch has the following change:
> 
> -#define MSGPOOL (MSGMNI*MSGMNB/1024)  /* size in kilobytes of message pool */
> +#define MSGPOOL (MSGMNI * MSGMNB) /* size in bytes of message pool */
> 
> Since this constitutes a kernel-userland interface change, so please
> do CC me, so that I can change the man pages if needed.

Oops, sorry for not doing it: I misunderstood the "unused"

> 
> The man page (http://www.kernel.org/doc/man-pages/online/pages/man2/msgctl.2.html)
> does indeed say that msgpool is "unused".  But that meant "unused by
> the kernel" (sorry -- I probably should have worded that text better).
>  And, as you spotted, the page also wrongly said the value is in
> bytes.
> 
> However, making this change affects the ABI.  A userspace application
> that was previously using msgctl(IPC_INFO) to retrieve the msgpool
> field will be affected by the factor-of-1024 change.  I strongly
> suspect that there no such applications, or certainly none that care
> (since this value is unused by the kernel).  But was there a reason
> for making this change, aside from the fact that the code and the man
> page didn't agree?
> 

No, that was the only reason.
Should I repost a patch to set it back as it used to be?

Regards
Nadia
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