From: Andrew Morton <akpm@linux-foundation.org>
To: Ed Cashin <ecashin@coraid.com>
Cc: <linux-kernel@vger.kernel.org>,
Christoph Hellwig <hch@infradead.org>, <linux-mm@kvack.org>
Subject: Re: [PATCH] aoe: adjust ref of head for compound page tails
Date: Wed, 7 Aug 2013 16:51:25 -0700 [thread overview]
Message-ID: <20130807165125.38a4acd2a8bc533e52d07d06@linux-foundation.org> (raw)
In-Reply-To: <3F0FBDD9-129C-45F4-A20C-3EB2E8EFC9C8@coraid.com>
On Wed, 7 Aug 2013 19:41:48 -0400 Ed Cashin <ecashin@coraid.com> wrote:
> On Aug 7, 2013, at 5:27 PM, Andrew Morton wrote:
>
> >> elevated refcount, full stop.
> >>
> >
> > err, no. slab.c uses alloc_pages(), so the underlying page indeed has
> > a proper refcount. I'm still not understanding how this situation comes
> > about.
>
> It sounds like it's wrong to give block pages with a zero count,
Depends on your definition of "page". It should be OK to put a
_count==0 tail page into a BIO, because the MM knows that it's a tail
page and that its refcount actually lives in the head page.
> so why not just have aoe BUG_ON(compound_trans_head(bv->page->_count) == 0) until we're sure nobody does that anymore?
AOE shouldn't be touching ->_count at all. That's why it has the
leading underscore. If AOE can stick with the usual interfaces such as
page_count(), everything should work?
next prev parent reply other threads:[~2013-08-07 23:51 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-02 1:29 [PATCH] aoe: respect compound page reference tracking expectations Ed Cashin
2013-08-02 1:29 ` [PATCH] aoe: adjust ref of head for compound page tails Ed Cashin
2013-08-07 20:58 ` Andrew Morton
2013-08-07 21:12 ` Ed Cashin
2013-08-07 21:18 ` Andrew Morton
2013-08-07 21:27 ` Andrew Morton
2013-08-07 23:41 ` Ed Cashin
2013-08-07 23:48 ` Ed Cashin
2013-08-07 23:51 ` Andrew Morton [this message]
2013-08-07 21:00 ` Andrew Morton
2013-08-07 21:21 ` Ed Cashin
2013-08-07 21:26 ` Andrew Morton
2013-08-07 23:27 ` Ed Cashin
2013-08-07 23:35 ` Andrew Morton
2013-08-07 23:54 ` Ed Cashin
2013-08-08 0:05 ` Andrew Morton
2013-08-08 0:50 ` Ed Cashin
2013-08-08 19:56 ` Andrew Morton
2013-08-08 21:02 ` Ed Cashin
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