linux-kernel - Re: [PATCH v5 3/7] mm, devm_memremap

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Date:   Fri, 14 Sep 2018 10:25:09 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        stable <stable@...r.kernel.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3/7] mm, devm_memremap_pages: Fix shutdown handling

On Fri, Sep 14, 2018 at 6:16 AM, Christoph Hellwig <hch@....de> wrote:
>> An argument could be made to require that the ->kill() operation be set
>> in the @pgmap arg rather than passed in separately. However, it helps
>> code readability, tracking the lifetime of a given instance, to be able
>> to grep the kill routine directly at the devm_memremap_pages() call
>> site.
>
> I generally do not like passing redundant argument, and I don't really
> see why this case is different.  Or in other ways I'd like to make
> your above argument..

Logan had similar feedback, and now the chorus is getting louder. I
personally like how I can do this with grep:

drivers/dax/pmem.c:114: addr = devm_memremap_pages(dev,
&dax_pmem->pgmap, dax_pmem_percpu_kill);
--
drivers/nvdimm/pmem.c:411:              addr =
devm_memremap_pages(dev, &pmem->pgmap,
drivers/nvdimm/pmem.c-412-                              pmem_freeze_queue);
--
drivers/nvdimm/pmem.c:425:              addr =
devm_memremap_pages(dev, &pmem->pgmap,
drivers/nvdimm/pmem.c-426-                              pmem_freeze_queue);
--
mm/hmm.c:1059:  result = devm_memremap_pages(devmem->device, &devmem->pagemap,
mm/hmm.c-1060-                  hmm_devmem_ref_kill);
--
mm/hmm.c:1113:  result = devm_memremap_pages(devmem->device, &devmem->pagemap,
mm/hmm.c-1114-                  hmm_devmem_ref_kill);

...and see all of the kill() variants, but the redundancy will likely
continue to bother folks.

> Except for that the patch looks good to me.

Thanks, I'll fix it up to drop the redundant arg.