linux-kernel - Re: [PATCH] nommu: Correct kobjsize() page validity checks.

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Message-ID: <2336.1213266053@redhat.com>
Date:	Thu, 12 Jun 2008 11:20:53 +0100
From:	David Howells <dhowells@...hat.com>
To:	Paul Mundt <lethal@...ux-sh.org>
Cc:	dhowells@...hat.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <clameter@....com>,
	Bryan Wu <cooloney@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nommu: Correct kobjsize() page validity checks.

David Howells <dhowells@...hat.com> wrote:

> Works for me.

Having said that, it doesn't produce the right answers under SLOB, with or
without this patch:

	void task_mem(struct seq_file *m, struct mm_struct *mm)
	{
		struct vm_list_struct *vml;
		unsigned long bytes = 0, sbytes = 0, slack = 0;

		down_read(&mm->mmap_sem);
		for (vml = mm->context.vmlist; vml; vml = vml->next) {
			if (!vml->vma)
				continue;

			bytes += kobjsize(vml);

Here kobjsize() returns 16384 (PAGE_SIZE) when it should return something a
lot smaller.  This appears related to SLOB not setting PG_slab, so
/proc/pic/status gets messed up:

	Mem:      983040 bytes
	Slack:     44112 bytes
	Shared:  1687552 bytes

SLAB returns 64 at this point, and in /proc/pid/status shows:

	Mem:      594016 bytes
	Slack:     44112 bytes
	Shared:  1638688 bytes

with or without the patch, which might even be correct.

Maybe on SLOB we want kobjsize() to become sizeof() where we're dealing with
fixed size units such as structs.  On the other hand, getting rid of
kobjsize() entirely would be good.

David
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