Re: [PATCH] mm: remove extra ZONE_DEVICE struct page refcount

Christoph Hellwig
2020-09-16T06:09:30Z

> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 517751310dd2..5a82037a4b26 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1093,34 +1093,6 @@ static inline bool is_zone_device_page(const struct page *page)
> #ifdef CONFIG_DEV_PAGEMAP_OPS
> void free_devmap_managed_page(struct page *page);
> DECLARE_STATIC_KEY_FALSE(devmap_managed_key);

The export for devmap_managed_key can be dropped now. In fact I think
we can remove devmap_managed_key entirely now - it is only checked in
the actual page free path instead of for each refcount manipulation,
so a good old unlikely is probably enough.

Also free_devmap_managed_page can move to mm/internal.h.

> +#ifdef CONFIG_DEV_PAGEMAP_OPS
> +static void __put_devmap_managed_page(struct page *page)
> +{
> + if (!static_branch_unlikely(&devmap_managed_key))
> + return;
> +
> + switch (page->pgmap->type) {
> + case MEMORY_DEVICE_PRIVATE:
> + case MEMORY_DEVICE_FS_DAX:
> + free_devmap_managed_page(page);
> + break;
> + default:
> + break;
> + }
> +}
> +#else
> +static inline void __put_devmap_managed_page(struct page *page)
> +{
> +}
> +#endif

I think this should be moved to mm/memremap.c or even better
actually be folded into free_devmap_managed_page, which would need
a new name like free_zone_device_page().

Something like this incremental patch:

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7bb9e93cf86cde..29350dc27cd0cd 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1090,11 +1090,6 @@ static inline bool is_zone_device_page(const struct page *page)
}
#endif

-#ifdef CONFIG_DEV_PAGEMAP_OPS
-void free_devmap_managed_page(struct page *page);
-DECLARE_STATIC_KEY_FALSE(devmap_managed_key);
-#endif /* CONFIG_DEV_PAGEMAP_OPS */
-
static inline bool is_device_private_page(const struct page *page)
{
return IS_ENABLED(CONFIG_DEV_PAGEMAP_OPS) &&
diff --git a/mm/internal.h b/mm/internal.h
index 6345b08ce86ccf..629959a6f26d7c 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -618,4 +618,12 @@ struct migration_target_control {
gfp_t gfp_mask;
};

+#ifdef CONFIG_DEV_PAGEMAP_OPS
+void free_zone_device_page(struct page *page);
+#else
+static inline void free_zone_device_page(struct page *page)
+{
+}
+#endif
+
#endif /* __MM_INTERNAL_H */
diff --git a/mm/memremap.c b/mm/memremap.c
index d549e3733f4098..b15ad2264a4f1c 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -12,6 +12,7 @@
#include <linux/types.h>
#include <linux/wait_bit.h>
#include <linux/xarray.h>
+#include "internal.h"

static DEFINE_XARRAY(pgmap_array);

@@ -37,36 +38,6 @@ unsigned long memremap_compat_align(void)
EXPORT_SYMBOL_GPL(memremap_compat_align);
#endif

-#ifdef CONFIG_DEV_PAGEMAP_OPS
-DEFINE_STATIC_KEY_FALSE(devmap_managed_key);
-EXPORT_SYMBOL(devmap_managed_key);
-
-static void devmap_managed_enable_put(void)
-{
- static_branch_dec(&devmap_managed_key);
-}
-
-static int devmap_managed_enable_get(struct dev_pagemap *pgmap)
-{
- if (pgmap->type == MEMORY_DEVICE_PRIVATE &&
- (!pgmap->ops || !pgmap->ops->page_free)) {
- WARN(1, "Missing page_free method\n");
- return -EINVAL;
- }
-
- static_branch_inc(&devmap_managed_key);
- return 0;
-}
-#else
-static int devmap_managed_enable_get(struct dev_pagemap *pgmap)
-{
- return -EINVAL;
-}
-static void devmap_managed_enable_put(void)
-{
-}
-#endif /* CONFIG_DEV_PAGEMAP_OPS */
-
static void pgmap_array_delete(struct range *range)
{
xa_store_range(&pgmap_array, PHYS_PFN(range->start), PHYS_PFN(range->end),
@@ -181,7 +152,6 @@ void memunmap_pages(struct dev_pagemap *pgmap)
pageunmap_range(pgmap, i);

WARN_ONCE(pgmap->altmap.alloc, "failed to free all reserved pages\n");
- devmap_managed_enable_put();
}
EXPORT_SYMBOL_GPL(memunmap_pages);

@@ -319,7 +289,6 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
.pgprot = PAGE_KERNEL,
};
const int nr_range = pgmap->nr_range;
- bool need_devmap_managed = true;
int error, i;

if (WARN_ONCE(!nr_range, "nr_range must be specified\n"))
@@ -331,8 +300,9 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
WARN(1, "Device private memory not supported\n");
return ERR_PTR(-EINVAL);
}
- if (!pgmap->ops || !pgmap->ops->migrate_to_ram) {
- WARN(1, "Missing migrate_to_ram method\n");
+ if (!pgmap->ops ||
+ !pgmap->ops->migrate_to_ram || !pgmap->ops->page_free) {
+ WARN(1, "Missing ops\n");
return ERR_PTR(-EINVAL);
}
if (!pgmap->owner) {
@@ -348,11 +318,9 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
}
break;
case MEMORY_DEVICE_GENERIC:
- need_devmap_managed = false;
break;
case MEMORY_DEVICE_PCI_P2PDMA:
params.pgprot = pgprot_noncached(params.pgprot);
- need_devmap_managed = false;
break;
default:
WARN(1, "Invalid pgmap type %d\n", pgmap->type);
@@ -376,12 +344,6 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
}
}

- if (need_devmap_managed) {
- error = devmap_managed_enable_get(pgmap);
- if (error)
- return ERR_PTR(error);
- }
-
/*
* Clear the pgmap nr_range as it will be incremented for each
* successfully processed range. This communicates how many
@@ -496,16 +458,9 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
EXPORT_SYMBOL_GPL(get_dev_pagemap);

#ifdef CONFIG_DEV_PAGEMAP_OPS
-void free_devmap_managed_page(struct page *page)
+static void free_device_private_page(struct page *page)
{
- /* notify page idle for dax */
- if (!is_device_private_page(page)) {
- wake_up_var(&page->_refcount);
- return;
- }
-
__ClearPageWaiters(page);
-
mem_cgroup_uncharge(page);

/*
@@ -540,4 +495,19 @@ void free_devmap_managed_page(struct page *page)
page->mapping = NULL;
page->pgmap->ops->page_free(page);
}
+
+void free_zone_device_page(struct page *page)
+{
+ switch (page->pgmap->type) {
+ case MEMORY_DEVICE_FS_DAX:
+ /* notify page idle */
+ wake_up_var(&page->_refcount);
+ return;
+ case MEMORY_DEVICE_PRIVATE:
+ free_device_private_page(page);
+ return;
+ default:
+ return;
+ }
+}
#endif /* CONFIG_DEV_PAGEMAP_OPS */
diff --git a/mm/swap.c b/mm/swap.c
index bcab5db351184a..83451ac70d0f05 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -113,36 +113,14 @@ static void __put_compound_page(struct page *page)
destroy_compound_page(page);
}

-#ifdef CONFIG_DEV_PAGEMAP_OPS
-static void __put_devmap_managed_page(struct page *page)
-{
- if (!static_branch_unlikely(&devmap_managed_key))
- return;
-
- switch (page->pgmap->type) {
- case MEMORY_DEVICE_PRIVATE:
- case MEMORY_DEVICE_FS_DAX:
- free_devmap_managed_page(page);
- break;
- default:
- break;
- }
-}
-#else
-static inline void __put_devmap_managed_page(struct page *page)
-{
-}
-#endif
-
void __put_page(struct page *page)
{
if (is_zone_device_page(page)) {
- __put_devmap_managed_page(page);
-
/*
* The page belongs to the device that created pgmap. Do
* not return it to page allocator.
*/
+ free_zone_device_page(page);
return;
}

@@ -923,7 +901,7 @@ void release_pages(struct page **pages, int nr)
flags);
locked_pgdat = NULL;
}
- __put_devmap_managed_page(page);
+ free_zone_device_page(page);
return;
}