linux-kernel - Re: Latest brk patchset

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Date:	Sat, 14 Mar 2009 23:03:39 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Yinghai Lu <yinghai@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Latest brk patchset

H. Peter Anvin wrote:
> On this subject, what is the point of the 64 K "slop space", and if it
> is necessary, why not just put it as a RESERVE_BRK() somewhere (*with* a
>  significant comment as to its necessity) instead of putting it as a
> hack in the linker script?
>   

Specifically, its to deal with space taken by alignment constraints.  At 
least some of the extend_brk() calls are page aligned, so that uses up 
to another 4k.  There are other ways to deal with it (pass an alignment 
to RESERVE_BRK and have it add it into the total, or just assume the 
user knows to include alignment overheads), but it seemed more 
straightforward to add some padding in the linker script.  After all, 
anything unused will get freed.  (But, yes, it could probably be 
documented as such, and 64k is a somewhat arbitrary number.)

    J
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