linux-kernel - Re: [PATCH] mm: Cleanup __put_devmap_managed_page() vs ->page

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Date:   Wed, 13 Nov 2019 16:47:38 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>,
        Ira Weiny <ira.weiny@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>
Subject: Re: [PATCH] mm: Cleanup __put_devmap_managed_page() vs ->page_free()

On Wed, Nov 13, 2019 at 4:42 PM John Hubbard <jhubbard@...dia.com> wrote:
>
> On 11/13/19 4:07 PM, Dan Williams wrote:
> > After the removal of the device-public infrastructure there are only 2
> > ->page_free() call backs in the kernel. One of those is a device-private
> > callback in the nouveau driver, the other is a generic wakeup needed in
> > the DAX case. In the hopes that all ->page_free() callbacks can be
> > migrated to common core kernel functionality, move the device-private
> > specific actions in __put_devmap_managed_page() under the
> > is_device_private_page() conditional, including the ->page_free()
> > callback. For the other page types just open-code the generic wakeup.
> >
> > Yes, the wakeup is only needed in the MEMORY_DEVICE_FSDAX case, but it
> > does no harm in the MEMORY_DEVICE_DEVDAX and MEMORY_DEVICE_PCI_P2PDMA
> > case.
> >
> > Cc: Jan Kara <jack@...e.cz>
> > Cc: Christoph Hellwig <hch@....de>
> > Cc: Ira Weiny <ira.weiny@...el.com>
> > Cc: Jérôme Glisse <jglisse@...hat.com>
> > Cc: John Hubbard <jhubbard@...dia.com>
> > Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> > ---
> > Hi John,
> >
> > This applies on top of today's linux-next and passes my nvdimm unit
> > tests. That testing noticed that devmap_managed_enable_get() needed a
> > small fixup as well.
>
> Got it. This will appear in the next posted version of my "mm/gup: track
> dma-pinned pages: FOLL_PIN, FOLL_LONGTERM" patchset.

Thanks!

>
>
> >
> >   drivers/nvdimm/pmem.c |    6 ------
> >   mm/memremap.c         |   22 ++++++++++++----------
> >   2 files changed, 12 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> > index f9f76f6ba07b..21db1ce8c0ae 100644
> > --- a/drivers/nvdimm/pmem.c
> > +++ b/drivers/nvdimm/pmem.c
> > @@ -338,13 +338,7 @@ static void pmem_release_disk(void *__pmem)
> >       put_disk(pmem->disk);
> >   }
> >
> > -static void pmem_pagemap_page_free(struct page *page)
> > -{
> > -     wake_up_var(&page->_refcount);
> > -}
> > -
> >   static const struct dev_pagemap_ops fsdax_pagemap_ops = {
> > -     .page_free              = pmem_pagemap_page_free,
> >       .kill                   = pmem_pagemap_kill,
> >       .cleanup                = pmem_pagemap_cleanup,
> >   };
> > diff --git a/mm/memremap.c b/mm/memremap.c
> > index 022e78e68ea0..6e6f3d6fdb73 100644
> > --- a/mm/memremap.c
> > +++ b/mm/memremap.c
> > @@ -27,7 +27,8 @@ static void devmap_managed_enable_put(void)
> >
> >   static int devmap_managed_enable_get(struct dev_pagemap *pgmap)
> >   {
> > -     if (!pgmap->ops || !pgmap->ops->page_free) {
> > +     if (!pgmap->ops || (pgmap->type == MEMORY_DEVICE_PRIVATE
> > +                             && !pgmap->ops->page_free)) {
>
>
> OK, so only MEMORY_DEVICE_PRIVATE has .page_free ops. That looks
> correct to me, based on looking at the .page_free setters--I
> only see Nouveau setting it.

Correct. The FSDAX case still needs to enable the 'devmap_managed_key'
static key, but other than that the core will handle all the follow-on
details.