linux-kernel - Re: [PATCH 12/17] mm: optimize dev_pagemap reference counting around get_dev

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Date:   Sun, 17 Dec 2017 09:28:49 -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 12/17] mm: optimize dev_pagemap reference counting around get_dev_pagemap

On Fri, Dec 15, 2017 at 6:09 AM, Christoph Hellwig <hch@....de> wrote:
> Change the calling convention so that get_dev_pagemap always consumes the
> previous reference instead of doing this using an explicit earlier call to
> put_dev_pagemap in the callers.
>
> The callers will still need to put the final reference after finishing the
> loop over the pages.
>
> Signed-off-by: Christoph Hellwig <hch@....de>
> Reviewed-by: Logan Gunthorpe <logang@...tatee.com>
> ---
>  kernel/memremap.c | 17 +++++++++--------
>  mm/gup.c          |  7 +++++--
>  2 files changed, 14 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index 43d94db97ff4..26764085785d 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -506,22 +506,23 @@ struct vmem_altmap *to_vmem_altmap(unsigned long memmap_start)
>   * @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.
> + * If @pgmap is non-NULL and covers @pfn it will be returned as-is.  If @pgmap
> + * is non-NULL but does not cover @pfn the reference to it while be released.

s/while/will/


Other than that you can add:

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