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SubjectRe: [HMM v13 04/18] mm/ZONE_DEVICE/free-page: callback when page is freed
On Mon, Nov 21, 2016 at 01:56:02PM +0530, Anshuman Khandual wrote:
> On 11/18/2016 11:48 PM, Jérôme Glisse wrote:
> > When a ZONE_DEVICE page refcount reach 1 it means it is free and nobody
> > is holding a reference on it (only device to which the memory belong do).
> > Add a callback and call it when that happen so device driver can implement
> > their own free page management.
> >
> > Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> > ---
> > include/linux/memremap.h | 4 ++++
> > kernel/memremap.c | 8 ++++++++
> > 2 files changed, 12 insertions(+)
> >
> > diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> > index fe61dca..469c88d 100644
> > --- a/include/linux/memremap.h
> > +++ b/include/linux/memremap.h
> > @@ -37,17 +37,21 @@ static inline struct vmem_altmap *to_vmem_altmap(unsigned long memmap_start)
> >
> > /**
> > * struct dev_pagemap - metadata for ZONE_DEVICE mappings
> > + * @free_devpage: free page callback when page refcount reach 1
> > * @altmap: pre-allocated/reserved memory for vmemmap allocations
> > * @res: physical address range covered by @ref
> > * @ref: reference count that pins the devm_memremap_pages() mapping
> > * @dev: host device of the mapping for debug
> > + * @data: privata data pointer for free_devpage
> > * @flags: memory flags (look for MEMORY_FLAGS_NONE in memory_hotplug.h)
> > */
> > struct dev_pagemap {
> > + void (*free_devpage)(struct page *page, void *data);
> > struct vmem_altmap *altmap;
> > const struct resource *res;
> > struct percpu_ref *ref;
> > struct device *dev;
> > + void *data;
> > int flags;
> > };
> >
> > diff --git a/kernel/memremap.c b/kernel/memremap.c
> > index 438a73aa2..3d28048 100644
> > --- a/kernel/memremap.c
> > +++ b/kernel/memremap.c
> > @@ -190,6 +190,12 @@ EXPORT_SYMBOL(get_zone_device_page);
> >
> > void put_zone_device_page(struct page *page)
> > {
> > + /*
> > + * If refcount is 1 then page is freed and refcount is stable as nobody
> > + * holds a reference on the page.
> > + */
> > + if (page->pgmap->free_devpage && page_count(page) == 1)
> > + page->pgmap->free_devpage(page, page->pgmap->data);
> > put_dev_pagemap(page->pgmap);
> > }
> > EXPORT_SYMBOL(put_zone_device_page);
> > @@ -326,6 +332,8 @@ void *devm_memremap_pages(struct device *dev, struct resource *res,
> > pgmap->ref = ref;
> > pgmap->res = &page_map->res;
> > pgmap->flags = flags | MEMORY_DEVICE;
> > + pgmap->free_devpage = NULL;
> > + pgmap->data = NULL;
>
> When is the driver expected to load up pgmap->free_devpage ? I thought
> this function is one of the right places. Though as all the pages in
> the same hotplug operation point to the same dev_pagemap structure this
> loading can be done at later point of time as well.
>

I wanted to avoid adding more argument to devm_memremap_pages() as it already
has a long list. Hence why i let the caller set those afterward.

Cheers,
Jérôme

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