linux-kernel - Re: [PATCH] reduce large do_mount stack usage with noinlines

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Message-ID: <47AC8931.50704@redhat.com>
Date:	Fri, 08 Feb 2008 10:54:09 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, rth@...hat.com
Subject: Re: [PATCH] reduce large do_mount stack usage with noinlines

Andi Kleen wrote:
> Andrew Morton <akpm@...ux-foundation.org> writes:
>>>   */
>>> -static int do_change_type(struct nameidata *nd, int flag)
>>> +static noinline int do_change_type(struct nameidata *nd, int flag)
>> What we could do here is defined a new noinline_because_of_stack_suckiness
>> and use that.  Reasons:
>>
>> - self-documenting, so we don't need to comment each site
>>
>> - can be made a no-op for suitable __GNUC__ values if gcc ever fixes this
> 
> In theory it should be already fixed; iirc Richard H. (cc'ed) added
> code for this somewhere in 4.x. Don't quite remember which x, likely 
> either 1 or 2.
> 
> e.g. if I do a quick test here on gcc 4.2 then it definitely
> reuses stack slots between inlines. As you can see only ~100 bytes
> are allocated, not ~200.

On gcc 4.1.2 and 4.3 (fedora flavors) I don't see it re-used in
do_mount, though... *shrug*

-Eric
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