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Date: Sat, 29 Apr 2017 16:18:38 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        =?iso-8859-1?B?Suly9G1l?= Glisse <jglisse@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Logan Gunthorpe <logang@deltatee.com>,
        Kirill Shutemov <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH v2] mm, zone_device: replace {get,
 put}_zone_device_page() with a single reference
Message-ID: <20170429141838.tkyfxhldmwypyipz@gmail.com>
References: <20170428063913.iz6xjcxblecofjlq@gmail.com>
 <149339998297.24933.1129582806028305912.stgit@dwillia2-desk3.amr.corp.intel.com>
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* Dan Williams <dan.j.williams@intel.com> wrote:

> Kirill points out that the calls to {get,put}_dev_pagemap() can be
> removed from the mm fast path if we take a single get_dev_pagemap()
> reference to signify that the page is alive and use the final put of the
> page to drop that reference.
> 
> This does require some care to make sure that any waits for the
> percpu_ref to drop to zero occur *after* devm_memremap_page_release(),
> since it now maintains its own elevated reference.
> 
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Jérôme Glisse <jglisse@redhat.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
> Suggested-by: Kirill Shutemov <kirill.shutemov@linux.intel.com>
> Tested-by: Kirill Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

This changelog is lacking an explanation about how this solves the crashes you 
were seeing.

Thanks,

	Ingo