linux-kernel - Re: [PATCH 11/17] mm: move get_dev

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Date:   Sun, 17 Dec 2017 09:26:20 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Jérôme Glisse <jglisse@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        X86 ML <x86@...nel.org>, Linux MM <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 11/17] mm: move get_dev_pagemap out of line

On Fri, Dec 15, 2017 at 6:09 AM, Christoph Hellwig <hch@....de> wrote:
> This is a pretty big function, which should be out of line in general,
> and a no-op stub if CONFIG_ZONE_DEVICЕ is not set.
>
> Signed-off-by: Christoph Hellwig <hch@....de>
> Reviewed-by: Logan Gunthorpe <logang@...tatee.com>
[..]
> +/**
> + * get_dev_pagemap() - take a new live reference on the dev_pagemap for @pfn
> + * @pfn: page frame number to lookup page_map
> + * @pgmap: optional known pgmap that already has a reference
> + *
> + * @pgmap allows the overhead of a lookup to be bypassed when @pfn lands in the
> + * same mapping.
> + */
> +struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
> +               struct dev_pagemap *pgmap)
> +{
> +       const struct resource *res = pgmap ? pgmap->res : NULL;
> +       resource_size_t phys = PFN_PHYS(pfn);
> +
> +       /*
> +        * In the cached case we're already holding a live reference so
> +        * we can simply do a blind increment
> +        */
> +       if (res && phys >= res->start && phys <= res->end) {
> +               percpu_ref_get(pgmap->ref);
> +               return pgmap;
> +       }

I was going to say keep the cached case in the static inline, but with
the optimization to the calling convention in the following patch I
think that makes this moot.

So,

Reviewed-by: Dan Williams <dan.j.williams@...el.com>