linux-kernel - Re: [PATCH v2] mm, zone_device: replace {get, put}_zone_device

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Message-ID: <20170429141838.tkyfxhldmwypyipz@gmail.com>
Date:   Sat, 29 Apr 2017 16:18:38 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Jérôme Glisse <jglisse@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v2] mm, zone_device: replace {get,
 put}_zone_device_page() with a single reference


* Dan Williams <dan.j.williams@...el.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@...hat.com>
> Cc: Jérôme Glisse <jglisse@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Reviewed-by: Logan Gunthorpe <logang@...tatee.com>
> Suggested-by: Kirill Shutemov <kirill.shutemov@...ux.intel.com>
> Tested-by: Kirill Shutemov <kirill.shutemov@...ux.intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>

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

Thanks,

	Ingo