linux-kernel - Re: [PATCH -mm 7/7] mm: thp: introduce compound_head_put_tail(), change get_futex

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Date:	Wed, 18 Dec 2013 20:40:25 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Jones <davej@...hat.com>,
	Darren Hart <dvhart@...ux.intel.com>,
	Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm 7/7] mm: thp: introduce compound_head_put_tail(),
	change get_futex_key() to use it

On 12/18, Peter Zijlstra wrote:
>
> On Wed, Dec 18, 2013 at 08:20:08PM +0100, Oleg Nesterov wrote:
> > +struct page *compound_head_put_tail(struct page *page)
> > +{
> > +	struct page *page_head;
> > +	unsigned long flags;
> > +
> > +	if (!PageTail(page))
> > +		return page;
> > +
> > +	page_head = compound_trans_head(page);
> > +
> > +	if (!__compound_tail_refcounted(page_head)) {
>
> This barrier is missing a comment describing the ordering and the
> pairing.

Yes, and this function lacks other comments it needs, they should be
copy-and-past'ed from the very similar __put_page_tail().

But I am going to unify them later if this series passes the review,
can't the comments wait till then?

OTOH, I won't mind to send v2 with the additional comment about this
rmb() at least. Or perhaps I should simply add /* See the comments in
__put_page_tail() */ into the new helper.

OK. But I'll wait for other reviews first.

Oleg.

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