linux-kernel - Re: [patch 2/3] MAP_NOZERO

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Date:	Tue, 26 Jun 2007 22:02:33 -0700
From:	"Ulrich Drepper" <drepper@...il.com>
To:	"Davide Libenzi" <davidel@...ilserver.org>
Cc:	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [patch 2/3] MAP_NOZERO - implement sys_brk2()

On 6/26/07, Davide Libenzi <davidel@...ilserver.org> wrote:
> I acutally have the code for it, but I never posted it since it did not
> receive a too warm review (and the only user was the fdmap thingy).

Only user of sys_indirect?  There will be quite a few right away.
Every syscall that returns a file descriptor needs O_CLOEXEC support
(socket, pipe, epoll_create, ...)

> OTOH glibc could implement __morecore using mmap(MAP_NOZERO), and hence
> brk2() would not be needed, no?

No.  mmap calls create individual VMAs which gets expensive.  There
are also some hardware drivers which get more expensive the more VMAs
there are.  I want to go away as much as possible from mmap for
malloc.
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