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

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Date:   Wed, 13 Nov 2019 16:39:17 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Dan Williams <dan.j.williams@...el.com>
CC:     Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>,
        Ira Weiny <ira.weiny@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        <linux-nvdimm@...ts.01.org>, <linux-kernel@...r.kernel.org>,
        <linux-mm@...ck.org>
Subject: Re: [PATCH] mm: Cleanup __put_devmap_managed_page() vs ->page_free()

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.


> 
>   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.


thanks,
-- 
John Hubbard
NVIDIA