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SubjectRe: [HMM v13 06/18] mm/ZONE_DEVICE/unaddressable: add special swap for unaddressable
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On 19/11/16 05:18, 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.
>
> 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);
> + }


So the reason there is a device swap entry for a page belonging to a user process is
that it is in the middle of migration or is it always that a swap entry represents
unaddressable memory belonging to a GPU device, but its tracked in the page table
entries of the process.

> } 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);
> 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));

Code style checks

> +}
> +
> +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);
> +
> + return page->pgmap->fault(vma, addr, page, flags, pmdp);
> +}
> +EXPORT_SYMBOL(device_entry_fault);
> +
> static void pgmap_radix_release(struct resource *res)
> {
> resource_size_t key, align_start, align_size, align_end;
> diff --git a/mm/Kconfig b/mm/Kconfig
> index be0ee11..0a21411 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -704,6 +704,18 @@ config ZONE_DEVICE
>
> If FS_DAX is enabled, then say Y.
>
> +config DEVICE_UNADDRESSABLE
> + bool "Un-addressable device memory (GPU memory, ...)"
> + depends on ZONE_DEVICE
> +
> + help
> + Allow to create struct page for un-addressable device memory
> + ie memory that is only accessible by the device (or group of
> + devices).
> +
> + This allow to migrate chunk of process memory to device memory
> + while that memory is use by the device.
> +
> config FRAME_VECTOR
> bool
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 15f2908..a83d690 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -889,6 +889,21 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
> pte = pte_swp_mksoft_dirty(pte);
> set_pte_at(src_mm, addr, src_pte, pte);
> }
> + } else if (is_device_entry(entry)) {
> + page = device_entry_to_page(entry);
> +
> + get_page(page);
> + rss[mm_counter(page)]++;

Why does rss count go up?

> + page_dup_rmap(page, false);
> +
> + if (is_write_device_entry(entry) &&
> + is_cow_mapping(vm_flags)) {
> + make_device_entry_read(&entry);
> + pte = swp_entry_to_pte(entry);
> + if (pte_swp_soft_dirty(*src_pte))
> + pte = pte_swp_mksoft_dirty(pte);
> + set_pte_at(src_mm, addr, src_pte, pte);
> + }
> }
> goto out_set_pte;
> }
> @@ -1191,6 +1206,12 @@ again:
>
> page = migration_entry_to_page(entry);
> rss[mm_counter(page)]--;
> + } else if (is_device_entry(entry)) {
> + struct page *page = device_entry_to_page(entry);
> + rss[mm_counter(page)]--;
> +
> + page_remove_rmap(page, false);
> + put_page(page);
> }
> if (unlikely(!free_swap_and_cache(entry)))
> print_bad_pte(vma, addr, ptent, NULL);
> @@ -2536,6 +2557,9 @@ int do_swap_page(struct fault_env *fe, pte_t orig_pte)
> if (unlikely(non_swap_entry(entry))) {
> if (is_migration_entry(entry)) {
> migration_entry_wait(vma->vm_mm, fe->pmd, fe->address);
> + } else if (is_device_entry(entry)) {
> + ret = device_entry_fault(vma, fe->address, entry,
> + fe->flags, fe->pmd);

What does device_entry_fault() actually do here?

> } else if (is_hwpoison_entry(entry)) {
> ret = VM_FAULT_HWPOISON;
> } else {
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index 1bc1eb3..70aff3a 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -139,6 +139,18 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
>
> pages++;
> }
> +
> + if (is_write_device_entry(entry)) {
> + pte_t newpte;
> +
> + make_device_entry_read(&entry);
> + newpte = swp_entry_to_pte(entry);
> + if (pte_swp_soft_dirty(oldpte))
> + newpte = pte_swp_mksoft_dirty(newpte);
> + set_pte_at(mm, addr, pte, newpte);
> +
> + pages++;
> + }

Does it make sense to call mprotect() on device memory ranges?

> }
> } while (pte++, addr += PAGE_SIZE, addr != end);
> arch_leave_lazy_mmu_mode();
>

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