linux-kernel - Re: [PATCH] mm: avoid tail page refcounting on non-THP compound pages

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Date:	Wed, 25 Mar 2015 16:09:38 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
cc:	Hugh Dickins <hughd@...gle.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: avoid tail page refcounting on non-THP compound
 pages

On Thu, 26 Mar 2015, Kirill A. Shutemov wrote:
> On Wed, Mar 25, 2015 at 03:48:48PM -0700, Hugh Dickins wrote:
> > On Wed, 25 Mar 2015, Hugh Dickins wrote:
> > > On Thu, 26 Mar 2015, Kirill A. Shutemov wrote:
> > > > 
> > > > Since currently all THP pages are anonymous and all drivers pages are
> > > > not, we can fix the __compound_tail_refcounted() check by requiring
> > > > PageAnon() to enable tail page refcounting.
> > > > 
> > > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > > 
> > > Acked-by: Hugh Dickins <hughd@...gle.com>
> > 
> > Oh, hold on a moment: does this actually build in a tree without your
> > page-flags.h consolidation?  It didn't when I tried to add a PageAnon
> > test there for my series against v3.19, has something changed in v4.0?
> 
> No. I haven't tried to build it without my patchset, but it seems it
> wouldn't.
> 
> Just check: it would build for me on top of [PATCH 01/16], you've acked.

Yes, I'm happy with your 1/16 (which is already there in mmotm),
it's just that I'd imagined this __compound_tail_refcounted() fix
should go to v4.0 (if not stable too: you've decided against, okay).

What do you think, should Andrew hold it back for v4.1, or should
your page-flags.h accelerate into v4.0 as precondition for this fix?

Either is fine with me; but if the latter, then a week's exposure
in linux-next first would probably be best.

Hugh
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