LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Andrew Morton <akpm@linux-foundation.org>
To: David Miller <davem@davemloft.net>
Cc: wcohen@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: Size of 2.6.20 task_struct on x86_64 machines
Date: Thu, 8 Feb 2007 13:03:00 -0800	[thread overview]
Message-ID: <20070208130300.e819bd7f.akpm@linux-foundation.org> (raw)
In-Reply-To: <20070208.121945.102574093.davem@davemloft.net>

On Thu, 08 Feb 2007 12:19:45 -0800 (PST)
David Miller <davem@davemloft.net> wrote:

> From: William Cohen <wcohen@redhat.com>
> Date: Thu, 08 Feb 2007 11:14:13 -0500
> 
> > This past week I was playing around with that pahole tool
> > (http://oops.ghostprotocols.net:81/acme/dwarves/) and looking at the
> > size of various struct in the kernel. I was surprised by the size of
> > the task_struct on x86_64, approaching 4K.  I looked through the
> > fields in task_struct and found that a number of them were declared as
> > "unsigned long" rather than "unsigned int" despite them appearing okay
> > as 32-bit sized fields. On x86_64 "unsigned long" ends up being 8
> > bytes in size and forces 8 byte alignment. Is there a reason there
> > a reason they are "unsigned long"?
> 
> I think at one point we used the atomic bit operations to operate on
> things like tsk->flags, and those interfaces require unsigned long as
> the type.
> 
> That doesn't appear to be the case any longer, so at a minimum
> your tsk->flags conversion to unsigned int should be ok.

Yeah, afacit everything in there is OK and happily all the
converted-to-32-bit quantities happen to be contiguous with other 32-bit
quantities.

Most architectures' bitops functions take unsigned long * so if anyone is
using bitops on these things we should get to hear about it.


  reply	other threads:[~2007-02-08 21:03 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-08 16:14 William Cohen
2007-02-08 20:19 ` David Miller
2007-02-08 21:03   ` Andrew Morton [this message]
2007-02-11  0:20 ` Dave Jones
2007-02-11  2:55   ` Linus Torvalds

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=20070208130300.e819bd7f.akpm@linux-foundation.org \
    --to=akpm@linux-foundation.org \
    --cc=davem@davemloft.net \
    --cc=linux-kernel@vger.kernel.org \
    --cc=wcohen@redhat.com \
    --subject='Re: Size of 2.6.20 task_struct on x86_64 machines' \
    /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).