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mm: introduce MEMORY_DEVICE_FS_DAX and CONFIG_DEV_PAGEMAP_OPS

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In preparation for fixing dax-dma-vs-unmap issues, filesystems need to
be able to rely on the fact that they will get wakeups on dev_pagemap
page-idle events. Introduce MEMORY_DEVICE_FS_DAX and
generic_dax_page_free() as common indicator / infrastructure for dax
filesytems to require. With this change there are no users of the
MEMORY_DEVICE_HOST designation, so remove it.

The HMM sub-system extended dev_pagemap to arrange a callback when a
dev_pagemap managed page is freed. Since a dev_pagemap page is free /
idle when its reference count is 1 it requires an additional branch to
check the page-type at put_page() time. Given put_page() is a hot-path
we do not want to incur that check if HMM is not in use, so a static
branch is used to avoid that overhead when not necessary.

Now, the FS_DAX implementation wants to reuse this mechanism for
receiving dev_pagemap ->page_free() callbacks. Rework the HMM-specific
static-key into a generic mechanism that either HMM or FS_DAX code paths
can enable.

For ARCH=um builds, and any other arch that lacks ZONE_DEVICE support,
care must be taken to compile out the DEV_PAGEMAP_OPS infrastructure.
However, we still need to support FS_DAX in the FS_DAX_LIMITED case
implemented by the s390/dcssblk driver.

Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Michal Hocko <[email protected]>
Reported-by: kbuild test robot <[email protected]>
Reported-by: Thomas Meyer <[email protected]>
Reported-by: Dave Jiang <[email protected]>
Cc: "Jérôme Glisse" <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Dan Williams <[email protected]>
This commit is contained in:
Dan Williams 2018-05-16 11:46:08 -07:00
commit e763848843
10 changed files with 137 additions and 65 deletions
Download patch file Download diff file Expand all files Collapse all files

32
kernel/memremap.c
View file

@ -9,6 +9,7 @@
#include <linux/memory_hotplug.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/wait_bit.h>
static DEFINE_MUTEX(pgmap_lock);
static RADIX_TREE(pgmap_radix, GFP_KERNEL);
@ -300,9 +301,32 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
return pgmap;
}
EXPORT_SYMBOL_GPL(get_dev_pagemap);
#if IS_ENABLED(CONFIG_DEVICE_PRIVATE) || IS_ENABLED(CONFIG_DEVICE_PUBLIC)
void put_zone_device_private_or_public_page(struct page *page)
#ifdef CONFIG_DEV_PAGEMAP_OPS
DEFINE_STATIC_KEY_FALSE(devmap_managed_key);
EXPORT_SYMBOL_GPL(devmap_managed_key);
static atomic_t devmap_enable;
/*
* Toggle the static key for ->page_free() callbacks when dev_pagemap
* pages go idle.
*/
void dev_pagemap_get_ops(void)
{
if (atomic_inc_return(&devmap_enable) == 1)
static_branch_enable(&devmap_managed_key);
}
EXPORT_SYMBOL_GPL(dev_pagemap_get_ops);
void dev_pagemap_put_ops(void)
{
if (atomic_dec_and_test(&devmap_enable))
static_branch_disable(&devmap_managed_key);
}
EXPORT_SYMBOL_GPL(dev_pagemap_put_ops);
void __put_devmap_managed_page(struct page *page)
{
int count = page_ref_dec_return(page);
@ -322,5 +346,5 @@ void put_zone_device_private_or_public_page(struct page *page)
} else if (!count)
__put_page(page);
}
EXPORT_SYMBOL(put_zone_device_private_or_public_page);
#endif /* CONFIG_DEVICE_PRIVATE || CONFIG_DEVICE_PUBLIC */
EXPORT_SYMBOL_GPL(__put_devmap_managed_page);
#endif /* CONFIG_DEV_PAGEMAP_OPS */