linux-kernel - Re: [PATCH -mm 4/7] mm: thp: turn put_compound_page() into __put_page

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Message-ID: <20131218195018.GA9290@redhat.com>
Date:	Wed, 18 Dec 2013 20:50:19 +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 4/7] mm: thp: turn put_compound_page() into
	__put_page_tail()

On 12/18, Peter Zijlstra wrote:
>
> On Wed, Dec 18, 2013 at 08:19:58PM +0100, Oleg Nesterov wrote:
> > @@ -247,7 +242,7 @@ bool __get_page_tail(struct page *page)
> >  	bool got;
> >  	struct page *page_head = compound_trans_head(page);
> >
> > -	/* Ref to put_compound_page() comment. */
> > +	/* Ref to __put_page_tail() comment. */
> >  	if (!__compound_tail_refcounted(page_head)) {
> >  		smp_rmb();
> >  		if (likely(PageTail(page))) {
>
> What code is this against, my local tree doesn't have that smp_rmb().

This is against -mm code.

> This suggests its a recent patch; which is good since then we can still
> drop it and wait for people to send one with a proper comment in.

put_compound_page() explains this barrier, this is what "Ref" above means,
I guess.

To remind, I think we can do more cleanups here.

Oleg.

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