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Date: Wed, 31 May 2017 14:09:04 +1000
From: Balbir Singh <bsingharora@...il.com>
To: Jérôme Glisse <jglisse@...hat.com>
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, Dan Williams <dan.j.williams@...el.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
John Hubbard <jhubbard@...dia.com>
Subject: Re: [HMM 14/15] mm/migrate: support un-addressable ZONE_DEVICE page
in migration v2
On Wed, 24 May 2017 13:20:23 -0400
Jérôme Glisse <jglisse@...hat.com> wrote:
> Allow to unmap and restore special swap entry of un-addressable
> ZONE_DEVICE memory.
>
> Changed since v1:
> - s/device unaddressable/device private/
>
> Signed-off-by: Jérôme Glisse <jglisse@...hat.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
> include/linux/migrate.h | 10 +++-
> mm/migrate.c | 134 ++++++++++++++++++++++++++++++++++++++----------
> mm/page_vma_mapped.c | 10 ++++
> mm/rmap.c | 25 +++++++++
> 4 files changed, 150 insertions(+), 29 deletions(-)
>
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 576b3f5..7dd875a 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -130,12 +130,18 @@ static inline int migrate_misplaced_transhuge_page(struct mm_struct *mm,
>
> #ifdef CONFIG_MIGRATION
>
> +/*
> + * Watch out for PAE architecture, which has an unsigned long, and might not
> + * have enough bits to store all physical address and flags. So far we have
> + * enough room for all our flags.
> + */
> #define MIGRATE_PFN_VALID (1UL << 0)
> #define MIGRATE_PFN_MIGRATE (1UL << 1)
> #define MIGRATE_PFN_LOCKED (1UL << 2)
> #define MIGRATE_PFN_WRITE (1UL << 3)
> -#define MIGRATE_PFN_ERROR (1UL << 4)
> -#define MIGRATE_PFN_SHIFT 5
> +#define MIGRATE_PFN_DEVICE (1UL << 4)
> +#define MIGRATE_PFN_ERROR (1UL << 5)
> +#define MIGRATE_PFN_SHIFT 6
>
> static inline struct page *migrate_pfn_to_page(unsigned long mpfn)
> {
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 1f2bc61..9e68399 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -36,6 +36,7 @@
> #include <linux/hugetlb.h>
> #include <linux/hugetlb_cgroup.h>
> #include <linux/gfp.h>
> +#include <linux/memremap.h>
> #include <linux/balloon_compaction.h>
> #include <linux/mmu_notifier.h>
> #include <linux/page_idle.h>
> @@ -227,7 +228,15 @@ static bool remove_migration_pte(struct page *page, struct vm_area_struct *vma,
> if (is_write_migration_entry(entry))
> pte = maybe_mkwrite(pte, vma);
>
> - flush_dcache_page(new);
> + if (unlikely(is_zone_device_page(new)) &&
> + is_device_private_page(new)) {
I would expect HMM-CDM to never hit this pattern, given that
we should not be creating migration entries for CDM memory.
Is that a fair assumption?
> + entry = make_device_private_entry(new, pte_write(pte));
> + pte = swp_entry_to_pte(entry);
> + if (pte_swp_soft_dirty(*pvmw.pte))
> + pte = pte_mksoft_dirty(pte);
> + } else
> + flush_dcache_page(new);
> +
> #ifdef CONFIG_HUGETLB_PAGE
> if (PageHuge(new)) {
> pte = pte_mkhuge(pte);
> @@ -2140,17 +2149,40 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
> pte = *ptep;
> pfn = pte_pfn(pte);
>
> - if (!pte_present(pte)) {
> + if (pte_none(pte)) {
> mpfn = pfn = 0;
> goto next;
> }
>
> + if (!pte_present(pte)) {
> + mpfn = pfn = 0;
> +
> + /*
> + * Only care about unaddressable device page special
> + * page table entry. Other special swap entries are not
> + * migratable, and we ignore regular swapped page.
> + */
> + entry = pte_to_swp_entry(pte);
> + if (!is_device_private_entry(entry))
> + goto next;
> +
> + page = device_private_entry_to_page(entry);
> + mpfn = migrate_pfn(page_to_pfn(page))|
> + MIGRATE_PFN_DEVICE | MIGRATE_PFN_MIGRATE;
> + if (is_write_device_private_entry(entry))
> + mpfn |= MIGRATE_PFN_WRITE;
> + } else {
> + page = vm_normal_page(migrate->vma, addr, pte);
> + mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
> + mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
> + }
> +
> /* FIXME support THP */
> - page = vm_normal_page(migrate->vma, addr, pte);
> if (!page || !page->mapping || PageTransCompound(page)) {
> mpfn = pfn = 0;
> goto next;
> }
> + pfn = page_to_pfn(page);
>
> /*
> * By getting a reference on the page we pin it and that blocks
> @@ -2163,8 +2195,6 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
> */
> get_page(page);
> migrate->cpages++;
> - mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
> - mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
>
> /*
> * Optimize for the common case where page is only mapped once
> @@ -2195,6 +2225,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
> }
>
> next:
> + migrate->dst[migrate->npages] = 0;
> migrate->src[migrate->npages++] = mpfn;
> }
> arch_leave_lazy_mmu_mode();
> @@ -2264,6 +2295,15 @@ static bool migrate_vma_check_page(struct page *page)
> if (PageCompound(page))
> return false;
>
> + /* Page from ZONE_DEVICE have one extra reference */
> + if (is_zone_device_page(page)) {
> + if (is_device_private_page(page)) {
> + extra++;
> + } else
> + /* Other ZONE_DEVICE memory type are not supported */
> + return false;
> + }
> +
> if ((page_count(page) - extra) > page_mapcount(page))
> return false;
>
> @@ -2301,24 +2341,30 @@ static void migrate_vma_prepare(struct migrate_vma *migrate)
> migrate->src[i] |= MIGRATE_PFN_LOCKED;
> }
>
> - if (!PageLRU(page) && allow_drain) {
> - /* Drain CPU's pagevec */
> - lru_add_drain_all();
> - allow_drain = false;
> - }
> + /* ZONE_DEVICE pages are not on LRU */
> + if (!is_zone_device_page(page)) {
> + if (!PageLRU(page) && allow_drain) {
> + /* Drain CPU's pagevec */
> + lru_add_drain_all();
> + allow_drain = false;
> + }
>
> - if (isolate_lru_page(page)) {
> - if (remap) {
> - migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
> - migrate->cpages--;
> - restore++;
> - } else {
> - migrate->src[i] = 0;
> - unlock_page(page);
> - migrate->cpages--;
> - put_page(page);
> + if (isolate_lru_page(page)) {
> + if (remap) {
> + migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
> + migrate->cpages--;
> + restore++;
> + } else {
> + migrate->src[i] = 0;
> + unlock_page(page);
> + migrate->cpages--;
> + put_page(page);
> + }
> + continue;
> }
> - continue;
> +
> + /* Drop the reference we took in collect */
> + put_page(page);
> }
>
> if (!migrate_vma_check_page(page)) {
> @@ -2327,14 +2373,19 @@ static void migrate_vma_prepare(struct migrate_vma *migrate)
> migrate->cpages--;
> restore++;
>
> - get_page(page);
> - putback_lru_page(page);
> + if (!is_zone_device_page(page)) {
> + get_page(page);
> + putback_lru_page(page);
> + }
> } else {
> migrate->src[i] = 0;
> unlock_page(page);
> migrate->cpages--;
>
> - putback_lru_page(page);
> + if (!is_zone_device_page(page))
> + putback_lru_page(page);
> + else
> + put_page(page);
> }
> }
> }
> @@ -2405,7 +2456,10 @@ static void migrate_vma_unmap(struct migrate_vma *migrate)
> unlock_page(page);
> restore--;
>
> - putback_lru_page(page);
> + if (is_zone_device_page(page))
> + put_page(page);
> + else
> + putback_lru_page(page);
> }
> }
>
> @@ -2436,6 +2490,26 @@ static void migrate_vma_pages(struct migrate_vma *migrate)
>
> mapping = page_mapping(page);
>
> + if (is_zone_device_page(newpage)) {
> + if (is_device_private_page(newpage)) {
> + /*
> + * For now only support private anonymous when
> + * migrating to un-addressable device memory.
> + */
> + if (mapping) {
> + migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
> + continue;
> + }
> + } else {
> + /*
> + * Other types of ZONE_DEVICE page are not
> + * supported.
> + */
> + migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
> + continue;
> + }
> + }
> +
> r = migrate_page(mapping, newpage, page, MIGRATE_SYNC_NO_COPY);
> if (r != MIGRATEPAGE_SUCCESS)
> migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
> @@ -2476,11 +2550,17 @@ static void migrate_vma_finalize(struct migrate_vma *migrate)
> unlock_page(page);
> migrate->cpages--;
>
> - putback_lru_page(page);
> + if (is_zone_device_page(page))
> + put_page(page);
> + else
> + putback_lru_page(page);
>
> if (newpage != page) {
> unlock_page(newpage);
> - putback_lru_page(newpage);
> + if (is_zone_device_page(newpage))
> + put_page(newpage);
> + else
> + putback_lru_page(newpage);
> }
> }
> }
> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> index de9c40d..f95765c 100644
> --- a/mm/page_vma_mapped.c
> +++ b/mm/page_vma_mapped.c
> @@ -48,6 +48,7 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw)
> if (!is_swap_pte(*pvmw->pte))
> return false;
> entry = pte_to_swp_entry(*pvmw->pte);
> +
> if (!is_migration_entry(entry))
> return false;
> if (migration_entry_to_page(entry) - pvmw->page >=
> @@ -60,6 +61,15 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw)
> WARN_ON_ONCE(1);
> #endif
> } else {
> + if (is_swap_pte(*pvmw->pte)) {
> + swp_entry_t entry;
> +
> + entry = pte_to_swp_entry(*pvmw->pte);
> + if (is_device_private_entry(entry) &&
> + device_private_entry_to_page(entry) == pvmw->page)
> + return true;
> + }
> +
> if (!pte_present(*pvmw->pte))
> return false;
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index d405f0e..515cea6 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -63,6 +63,7 @@
> #include <linux/hugetlb.h>
> #include <linux/backing-dev.h>
> #include <linux/page_idle.h>
> +#include <linux/memremap.h>
>
> #include <asm/tlbflush.h>
>
> @@ -1308,6 +1309,10 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> if ((flags & TTU_MUNLOCK) && !(vma->vm_flags & VM_LOCKED))
> return true;
>
> + if (IS_ENABLED(CONFIG_MIGRATION) && (flags & TTU_MIGRATION) &&
> + is_zone_device_page(page) && !is_device_private_page(page))
> + return true;
> +
I wonder how CDM would ever work with this?
> if (flags & TTU_SPLIT_HUGE_PMD) {
> split_huge_pmd_address(vma, address,
> flags & TTU_MIGRATION, page);
> @@ -1343,6 +1348,26 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
> subpage = page - page_to_pfn(page) + pte_pfn(*pvmw.pte);
> address = pvmw.address;
>
> + if (IS_ENABLED(CONFIG_MIGRATION) &&
> + (flags & TTU_MIGRATION) &&
> + is_zone_device_page(page)) {
> + swp_entry_t entry;
> + pte_t swp_pte;
> +
> + pteval = ptep_get_and_clear(mm, address, pvmw.pte);
> +
> + /*
> + * Store the pfn of the page in a special migration
> + * pte. do_swap_page() will wait until the migration
> + * pte is removed and then restart fault handling.
> + */
> + entry = make_migration_entry(page, 0);
> + swp_pte = swp_entry_to_pte(entry);
> + if (pte_soft_dirty(pteval))
> + swp_pte = pte_swp_mksoft_dirty(swp_pte);
> + set_pte_at(mm, address, pvmw.pte, swp_pte);
> + goto discard;
> + }
>
> if (!(flags & TTU_IGNORE_ACCESS)) {
> if (ptep_clear_flush_young_notify(vma, address,
Balbir Singh
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