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    SubjectRe: [HMM v13 06/18] mm/ZONE_DEVICE/unaddressable: add special swap for unaddressable
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    On 11/18/2016 11:48 PM, Jérôme Glisse wrote:
    > To allow use of device un-addressable memory inside a process add a
    > special swap type. Also add a new callback to handle page fault on
    > such entry.

    IIUC this swap type is required only for the mirror cases and its
    not a requirement for migration. If it's required for mirroring
    purpose where we intercept each page fault, the commit message
    here should clearly elaborate on that more.

    >
    > Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
    > Cc: Dan Williams <dan.j.williams@intel.com>
    > Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
    > ---
    > fs/proc/task_mmu.c | 10 +++++++-
    > include/linux/memremap.h | 5 ++++
    > include/linux/swap.h | 18 ++++++++++---
    > include/linux/swapops.h | 67 ++++++++++++++++++++++++++++++++++++++++++++++++
    > kernel/memremap.c | 14 ++++++++++
    > mm/Kconfig | 12 +++++++++
    > mm/memory.c | 24 +++++++++++++++++
    > mm/mprotect.c | 12 +++++++++
    > 8 files changed, 158 insertions(+), 4 deletions(-)
    >
    > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
    > index 6909582..0726d39 100644
    > --- a/fs/proc/task_mmu.c
    > +++ b/fs/proc/task_mmu.c
    > @@ -544,8 +544,11 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
    > } else {
    > mss->swap_pss += (u64)PAGE_SIZE << PSS_SHIFT;
    > }
    > - } else if (is_migration_entry(swpent))
    > + } else if (is_migration_entry(swpent)) {
    > page = migration_entry_to_page(swpent);
    > + } else if (is_device_entry(swpent)) {
    > + page = device_entry_to_page(swpent);
    > + }
    > } else if (unlikely(IS_ENABLED(CONFIG_SHMEM) && mss->check_shmem_swap
    > && pte_none(*pte))) {
    > page = find_get_entry(vma->vm_file->f_mapping,
    > @@ -708,6 +711,8 @@ static int smaps_hugetlb_range(pte_t *pte, unsigned long hmask,
    >
    > if (is_migration_entry(swpent))
    > page = migration_entry_to_page(swpent);
    > + if (is_device_entry(swpent))
    > + page = device_entry_to_page(swpent);
    > }
    > if (page) {
    > int mapcount = page_mapcount(page);
    > @@ -1191,6 +1196,9 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
    > flags |= PM_SWAP;
    > if (is_migration_entry(entry))
    > page = migration_entry_to_page(entry);
    > +
    > + if (is_device_entry(entry))
    > + page = device_entry_to_page(entry);
    > }
    >
    > if (page && !PageAnon(page))
    > diff --git a/include/linux/memremap.h b/include/linux/memremap.h
    > index b6f03e9..d584c74 100644
    > --- a/include/linux/memremap.h
    > +++ b/include/linux/memremap.h
    > @@ -47,6 +47,11 @@ static inline struct vmem_altmap *to_vmem_altmap(unsigned long memmap_start)
    > */
    > struct dev_pagemap {
    > void (*free_devpage)(struct page *page, void *data);
    > + int (*fault)(struct vm_area_struct *vma,
    > + unsigned long addr,
    > + struct page *page,
    > + unsigned flags,
    > + pmd_t *pmdp);

    We are extending the dev_pagemap once again to accommodate device driver
    specific fault routines for these pages. Wondering if this extension and
    the new swap type should be in the same patch.

    > struct vmem_altmap *altmap;
    > const struct resource *res;
    > struct percpu_ref *ref;
    > diff --git a/include/linux/swap.h b/include/linux/swap.h
    > index 7e553e1..599cb54 100644
    > --- a/include/linux/swap.h
    > +++ b/include/linux/swap.h
    > @@ -50,6 +50,17 @@ static inline int current_is_kswapd(void)
    > */
    >
    > /*
    > + * Un-addressable device memory support
    > + */
    > +#ifdef CONFIG_DEVICE_UNADDRESSABLE
    > +#define SWP_DEVICE_NUM 2
    > +#define SWP_DEVICE_WRITE (MAX_SWAPFILES + SWP_HWPOISON_NUM + SWP_MIGRATION_NUM)
    > +#define SWP_DEVICE (MAX_SWAPFILES + SWP_HWPOISON_NUM + SWP_MIGRATION_NUM + 1)
    > +#else
    > +#define SWP_DEVICE_NUM 0
    > +#endif
    > +
    > +/*
    > * NUMA node memory migration support
    > */
    > #ifdef CONFIG_MIGRATION
    > @@ -71,7 +82,8 @@ static inline int current_is_kswapd(void)
    > #endif
    >
    > #define MAX_SWAPFILES \
    > - ((1 << MAX_SWAPFILES_SHIFT) - SWP_MIGRATION_NUM - SWP_HWPOISON_NUM)
    > + ((1 << MAX_SWAPFILES_SHIFT) - SWP_DEVICE_NUM - \
    > + SWP_MIGRATION_NUM - SWP_HWPOISON_NUM)
    >
    > /*
    > * Magic header for a swap area. The first part of the union is
    > @@ -442,8 +454,8 @@ static inline void show_swap_cache_info(void)
    > {
    > }
    >
    > -#define free_swap_and_cache(swp) is_migration_entry(swp)
    > -#define swapcache_prepare(swp) is_migration_entry(swp)
    > +#define free_swap_and_cache(e) (is_migration_entry(e) || is_device_entry(e))
    > +#define swapcache_prepare(e) (is_migration_entry(e) || is_device_entry(e))
    >
    > static inline int add_swap_count_continuation(swp_entry_t swp, gfp_t gfp_mask)
    > {
    > diff --git a/include/linux/swapops.h b/include/linux/swapops.h
    > index 5c3a5f3..d1aa425 100644
    > --- a/include/linux/swapops.h
    > +++ b/include/linux/swapops.h
    > @@ -100,6 +100,73 @@ static inline void *swp_to_radix_entry(swp_entry_t entry)
    > return (void *)(value | RADIX_TREE_EXCEPTIONAL_ENTRY);
    > }
    >
    > +#ifdef CONFIG_DEVICE_UNADDRESSABLE
    > +static inline swp_entry_t make_device_entry(struct page *page, bool write)
    > +{
    > + return swp_entry(write?SWP_DEVICE_WRITE:SWP_DEVICE, page_to_pfn(page));
    > +}
    > +
    > +static inline bool is_device_entry(swp_entry_t entry)
    > +{
    > + int type = swp_type(entry);
    > + return type == SWP_DEVICE || type == SWP_DEVICE_WRITE;
    > +}
    > +
    > +static inline void make_device_entry_read(swp_entry_t *entry)
    > +{
    > + *entry = swp_entry(SWP_DEVICE, swp_offset(*entry));
    > +}
    > +
    > +static inline bool is_write_device_entry(swp_entry_t entry)
    > +{
    > + return unlikely(swp_type(entry) == SWP_DEVICE_WRITE);
    > +}
    > +
    > +static inline struct page *device_entry_to_page(swp_entry_t entry)
    > +{
    > + return pfn_to_page(swp_offset(entry));
    > +}
    > +
    > +int device_entry_fault(struct vm_area_struct *vma,
    > + unsigned long addr,
    > + swp_entry_t entry,
    > + unsigned flags,
    > + pmd_t *pmdp);
    > +#else /* CONFIG_DEVICE_UNADDRESSABLE */
    > +static inline swp_entry_t make_device_entry(struct page *page, bool write)
    > +{
    > + return swp_entry(0, 0);
    > +}
    > +
    > +static inline void make_device_entry_read(swp_entry_t *entry)
    > +{
    > +}
    > +
    > +static inline bool is_device_entry(swp_entry_t entry)
    > +{
    > + return false;
    > +}
    > +
    > +static inline bool is_write_device_entry(swp_entry_t entry)
    > +{
    > + return false;
    > +}
    > +
    > +static inline struct page *device_entry_to_page(swp_entry_t entry)
    > +{
    > + return NULL;
    > +}
    > +
    > +static inline int device_entry_fault(struct vm_area_struct *vma,
    > + unsigned long addr,
    > + swp_entry_t entry,
    > + unsigned flags,
    > + pmd_t *pmdp)
    > +{
    > + return VM_FAULT_SIGBUS;
    > +}
    > +#endif /* CONFIG_DEVICE_UNADDRESSABLE */
    > +
    > #ifdef CONFIG_MIGRATION
    > static inline swp_entry_t make_migration_entry(struct page *page, int write)
    > {
    > diff --git a/kernel/memremap.c b/kernel/memremap.c
    > index cf83928..0670015 100644
    > --- a/kernel/memremap.c
    > +++ b/kernel/memremap.c
    > @@ -18,6 +18,8 @@
    > #include <linux/io.h>
    > #include <linux/mm.h>
    > #include <linux/memory_hotplug.h>
    > +#include <linux/swap.h>
    > +#include <linux/swapops.h>
    >
    > #ifndef ioremap_cache
    > /* temporary while we convert existing ioremap_cache users to memremap */
    > @@ -200,6 +202,18 @@ void put_zone_device_page(struct page *page)
    > }
    > EXPORT_SYMBOL(put_zone_device_page);
    >
    > +int device_entry_fault(struct vm_area_struct *vma,
    > + unsigned long addr,
    > + swp_entry_t entry,
    > + unsigned flags,
    > + pmd_t *pmdp)
    > +{
    > + struct page *page = device_entry_to_page(entry);
    > +

    A BUG_ON() if page->pgmap->fault has not been populated by the driver.

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