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Date: Mon, 21 Nov 2016 16:40:54 +0530
From: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To: Balbir Singh <bsingharora@...il.com>,
Jérôme Glisse <jglisse@...hat.com>,
akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Cc: John Hubbard <jhubbard@...dia.com>,
Dan Williams <dan.j.williams@...el.com>,
Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: Re: [HMM v13 06/18] mm/ZONE_DEVICE/unaddressable: add special swap
for unaddressable
On 11/21/2016 07:36 AM, Balbir Singh wrote:
>
>
> 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@...hat.com>
>> Cc: Dan Williams <dan.j.williams@...el.com>
>> Cc: Ross Zwisler <ross.zwisler@...ux.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.
I guess the later is the case and its used for the page table mirroring
purpose after intercepting the page faults. But will leave upto Jerome
to explain more on this.
>
>> } 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?
IIUC it calls page->pgmap->fault() which is device specific page fault for
the page and thats how the control reaches device driver from the core VM.
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