LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Andrew Morton <akpm@linux-foundation.org>
To: Eric Sandeen <sandeen@redhat.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] reduce large do_mount stack usage with noinlines
Date: Wed, 6 Feb 2008 14:34:57 -0800	[thread overview]
Message-ID: <20080206143457.03e8741d.akpm@linux-foundation.org> (raw)
In-Reply-To: <47AA3126.8090102@redhat.com>

On Wed, 06 Feb 2008 16:13:58 -0600
Eric Sandeen <sandeen@redhat.com> wrote:

> do_mount() uses a whopping 616 bytes of stack on x86_64 in 
> 2.6.24-mm1, largely thanks to gcc inlining the various helper 
> functions.

hm, sizeof(nameidata)=136 and I can see about three of them on the stack. 
Must have missed something.

> noinlining these can slim it down a lot; on my box this patch
> gets it down to 168, which is mostly the struct nameidata nd;
> left on the stack.
> 
> These functions are called only as do_mount() helpers;
> none of them should be in any path that would see a performance
> benefit from inlining...
> 

Does the patch actually help?  I mean, if a() calls b() and both use N
bytes of locals, our worst-case stack usage remains ~2N whether or not b()
was inlined in a()?  In fact, uninlining makes things a little worse due to
callframe stuff.

> -static int do_change_type(struct nameidata *nd, int flag)
> +static noinline int do_change_type(struct nameidata *nd, int flag)

There's no way for the reader to work out why this is here, so I do think
it should be commented somewhere.


  reply	other threads:[~2008-02-06 22:35 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-06 22:13 Eric Sandeen
2008-02-06 22:34 ` Andrew Morton [this message]
2008-02-06 22:54   ` Arjan van de Ven
2008-02-06 23:01     ` Eric Sandeen
2008-02-06 22:55   ` Eric Sandeen
2008-02-06 23:11   ` Eric Sandeen
2008-02-06 23:22     ` Andrew Morton
2008-02-06 23:34       ` Eric Sandeen
2008-02-06 23:46         ` Andrew Morton
2008-02-07 23:08       ` Eric Sandeen
2008-02-07 23:23         ` Arjan van de Ven
2008-02-07 23:26         ` Andrew Morton
2008-02-08 16:50       ` Andi Kleen
2008-02-08 16:54         ` Eric Sandeen
2008-02-08 17:23           ` Al Viro

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20080206143457.03e8741d.akpm@linux-foundation.org \
    --to=akpm@linux-foundation.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=sandeen@redhat.com \
    --subject='Re: [PATCH] reduce large do_mount stack usage with noinlines' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).