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Subject[RFC PATCH v2 21/30] mm: thp: PUD THP support in try_to_unmap().
Date
From: Zi Yan <ziy@nvidia.com>

Unmap different subpages in different sized THPs properly in the
try_to_unmap() function. pvmw.pte, pvmw.pmd, pvmw.pud are used to
identify unmapped page sizes:

1. pvmw.pte != NULL: PTE pages or PageHuge.
2. pvmw.pte == NULL and pvmw.pmd != NULL: PMD pages.
3. pvmw.pte == NULL and pvmw.pmd == NULL and pvmw.pud != NULL: PUD pages.

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
mm/migrate.c | 2 +-
mm/rmap.c | 156 ++++++++++++++++++++++++++++++++++++++-------------
2 files changed, 117 insertions(+), 41 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index a7320e9d859c..d0e6afe682aa 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -225,7 +225,7 @@ static bool remove_migration_pte(struct page *page, struct vm_area_struct *vma,

#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
/* PMD-mapped THP migration entry */
- if (!pvmw.pte) {
+ if (!pvmw.pte && pvmw.pmd) {
VM_BUG_ON_PAGE(PageHuge(page) || !PageTransCompound(page), page);
remove_migration_pmd(&pvmw, new);
continue;
diff --git a/mm/rmap.c b/mm/rmap.c
index 424322807966..32f2e0312e16 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1125,6 +1125,7 @@ void do_page_add_anon_rmap(struct page *page,
{
bool compound = flags & RMAP_COMPOUND;
bool first;
+ struct page *head = compound_head(page);

if (unlikely(PageKsm(page)))
lock_page_memcg(page);
@@ -1134,7 +1135,7 @@ void do_page_add_anon_rmap(struct page *page,
if (compound) {
atomic_t *mapcount = NULL;
VM_BUG_ON_PAGE(!PageLocked(page), page);
- VM_BUG_ON_PAGE(!PageTransHuge(page), page);
+ VM_BUG_ON_PAGE(!PMDPageInPUD(page) && !PageTransHuge(page), page);
if (compound_order(page) == HPAGE_PUD_ORDER) {
if (map_order == HPAGE_PUD_ORDER) {
mapcount = compound_mapcount_ptr(page);
@@ -1143,7 +1144,7 @@ void do_page_add_anon_rmap(struct page *page,
mapcount = sub_compound_mapcount_ptr(page, 1);
} else
VM_BUG_ON(1);
- } else if (compound_order(page) == HPAGE_PMD_ORDER) {
+ } else if (compound_order(head) == HPAGE_PMD_ORDER) {
mapcount = compound_mapcount_ptr(page);
} else
VM_BUG_ON(1);
@@ -1153,7 +1154,7 @@ void do_page_add_anon_rmap(struct page *page,
}

if (first) {
- int nr = compound ? thp_nr_pages(page) : 1;
+ int nr = 1<<map_order;
/*
* We use the irq-unsafe __{inc|mod}_zone_page_stat because
* these counters are not modified in interrupt context, and
@@ -1474,10 +1475,13 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
.address = address,
};
pte_t pteval;
- struct page *subpage;
+ pmd_t pmdval;
+ pud_t pudval;
+ struct page *subpage = NULL;
bool ret = true;
struct mmu_notifier_range range;
enum ttu_flags flags = (enum ttu_flags)(long)arg;
+ int map_order = 0;

/* munlock has nothing to gain from examining un-locked vmas */
if ((flags & TTU_MUNLOCK) && !(vma->vm_flags & VM_LOCKED))
@@ -1487,6 +1491,11 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
is_zone_device_page(page) && !is_device_private_page(page))
return true;

+ if (flags & TTU_SPLIT_HUGE_PUD) {
+ split_huge_pud_address(vma, address,
+ flags & TTU_SPLIT_FREEZE, page);
+ }
+
if (flags & TTU_SPLIT_HUGE_PMD) {
split_huge_pmd_address(vma, address,
flags & TTU_SPLIT_FREEZE, page);
@@ -1519,7 +1528,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
while (page_vma_mapped_walk(&pvmw)) {
#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
/* PMD-mapped THP migration entry */
- if (!pvmw.pte && (flags & TTU_MIGRATION)) {
+ if (!pvmw.pte && pvmw.pmd && (flags & TTU_MIGRATION)) {
VM_BUG_ON_PAGE(PageHuge(page) || !PageTransCompound(page), page);

set_pmd_migration_entry(&pvmw, page);
@@ -1551,9 +1560,25 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
}

/* Unexpected PMD-mapped THP? */
- VM_BUG_ON_PAGE(!pvmw.pte, page);

- subpage = page - page_to_pfn(page) + pte_pfn(*pvmw.pte);
+ if (pvmw.pte) {
+ subpage = page - page_to_pfn(page) + pte_pfn(*pvmw.pte);
+ /*
+ * PageHuge always uses pvmw.pte to store relevant page
+ * table entry
+ */
+ if (PageHuge(page))
+ map_order = compound_order(page);
+ else
+ map_order = 0;
+ } else if (!pvmw.pte && pvmw.pmd) {
+ subpage = page - page_to_pfn(page) + pmd_pfn(*pvmw.pmd);
+ map_order = HPAGE_PMD_ORDER;
+ } else if (!pvmw.pte && !pvmw.pmd && pvmw.pud) {
+ subpage = page - page_to_pfn(page) + pud_pfn(*pvmw.pud);
+ map_order = HPAGE_PUD_ORDER;
+ }
+ VM_BUG_ON(!subpage);
address = pvmw.address;

if (PageHuge(page)) {
@@ -1631,8 +1656,12 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
}

if (!(flags & TTU_IGNORE_ACCESS)) {
- if (ptep_clear_flush_young_notify(vma, address,
- pvmw.pte)) {
+ if ((pvmw.pte &&
+ ptep_clear_flush_young_notify(vma, address, pvmw.pte)) ||
+ ((!pvmw.pte && pvmw.pmd) &&
+ pmdp_clear_flush_young_notify(vma, address, pvmw.pmd)) ||
+ ((!pvmw.pte && !pvmw.pmd && pvmw.pud) &&
+ pudp_clear_flush_young_notify(vma, address, pvmw.pud))) {
ret = false;
page_vma_mapped_walk_done(&pvmw);
break;
@@ -1640,7 +1669,12 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
}

/* Nuke the page table entry. */
- flush_cache_page(vma, address, pte_pfn(*pvmw.pte));
+ if (pvmw.pte)
+ flush_cache_page(vma, address, pte_pfn(*pvmw.pte));
+ else if (!pvmw.pte && pvmw.pmd)
+ flush_cache_page(vma, address, pmd_pfn(*pvmw.pmd));
+ else if (!pvmw.pte && !pvmw.pmd && pvmw.pud)
+ flush_cache_page(vma, address, pud_pfn(*pvmw.pud));
if (should_defer_flush(mm, flags)) {
/*
* We clear the PTE but do not flush so potentially
@@ -1650,16 +1684,34 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
* transition on a cached TLB entry is written through
* and traps if the PTE is unmapped.
*/
- pteval = ptep_get_and_clear(mm, address, pvmw.pte);
+ if (pvmw.pte) {
+ pteval = ptep_get_and_clear(mm, address, pvmw.pte);
+
+ set_tlb_ubc_flush_pending(mm, pte_dirty(pteval));
+ } else if (!pvmw.pte && pvmw.pmd) {
+ pmdval = pmdp_huge_get_and_clear(mm, address, pvmw.pmd);

- set_tlb_ubc_flush_pending(mm, pte_dirty(pteval));
+ set_tlb_ubc_flush_pending(mm, pmd_dirty(pmdval));
+ } else if (!pvmw.pte && !pvmw.pmd && pvmw.pud) {
+ pudval = pudp_huge_get_and_clear(mm, address, pvmw.pud);
+
+ set_tlb_ubc_flush_pending(mm, pud_dirty(pudval));
+ }
} else {
- pteval = ptep_clear_flush(vma, address, pvmw.pte);
+ if (pvmw.pte)
+ pteval = ptep_clear_flush(vma, address, pvmw.pte);
+ else if (!pvmw.pte && pvmw.pmd)
+ pmdval = pmdp_huge_clear_flush(vma, address, pvmw.pmd);
+ else if (!pvmw.pte && !pvmw.pmd && pvmw.pud)
+ pudval = pudp_huge_clear_flush(vma, address, pvmw.pud);
}

/* Move the dirty bit to the page. Now the pte is gone. */
- if (pte_dirty(pteval))
- set_page_dirty(page);
+ if ((pvmw.pte && pte_dirty(pteval)) ||
+ ((!pvmw.pte && pvmw.pmd) && pmd_dirty(pmdval)) ||
+ ((!pvmw.pte && !pvmw.pmd && pvmw.pud) && pud_dirty(pudval))
+ )
+ set_page_dirty(page);

/* Update high watermark before we lower rss */
update_hiwater_rss(mm);
@@ -1694,35 +1746,59 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
} else if (IS_ENABLED(CONFIG_MIGRATION) &&
(flags & (TTU_MIGRATION|TTU_SPLIT_FREEZE))) {
swp_entry_t entry;
- pte_t swp_pte;

- if (arch_unmap_one(mm, vma, address, pteval) < 0) {
- set_pte_at(mm, address, pvmw.pte, pteval);
- ret = false;
- page_vma_mapped_walk_done(&pvmw);
- break;
- }
+ if (pvmw.pte) {
+ pte_t swp_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(subpage,
- pte_write(pteval));
- swp_pte = swp_entry_to_pte(entry);
- if (pte_soft_dirty(pteval))
- swp_pte = pte_swp_mksoft_dirty(swp_pte);
- if (pte_uffd_wp(pteval))
- swp_pte = pte_swp_mkuffd_wp(swp_pte);
- set_pte_at(mm, address, pvmw.pte, swp_pte);
- /*
- * No need to invalidate here it will synchronize on
- * against the special swap migration pte.
- */
+ if (arch_unmap_one(mm, vma, address, pteval) < 0) {
+ set_pte_at(mm, address, pvmw.pte, pteval);
+ ret = false;
+ page_vma_mapped_walk_done(&pvmw);
+ break;
+ }
+
+ /*
+ * 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(subpage,
+ pte_write(pteval));
+ swp_pte = swp_entry_to_pte(entry);
+ if (pte_soft_dirty(pteval))
+ swp_pte = pte_swp_mksoft_dirty(swp_pte);
+ if (pte_uffd_wp(pteval))
+ swp_pte = pte_swp_mkuffd_wp(swp_pte);
+ set_pte_at(mm, address, pvmw.pte, swp_pte);
+ /*
+ * No need to invalidate here it will synchronize on
+ * against the special swap migration pte.
+ */
+ } else if (!pvmw.pte && pvmw.pmd) {
+ pmd_t swp_pmd;
+ /*
+ * 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(subpage,
+ pmd_write(pmdval));
+ swp_pmd = swp_entry_to_pmd(entry);
+ if (pmd_soft_dirty(pmdval))
+ swp_pmd = pmd_swp_mksoft_dirty(swp_pmd);
+ set_pmd_at(mm, address, pvmw.pmd, swp_pmd);
+ /*
+ * No need to invalidate here it will synchronize on
+ * against the special swap migration pte.
+ */
+ } else if (!pvmw.pte && !pvmw.pmd && pvmw.pud) {
+ VM_BUG_ON(1);
+ }
} else if (PageAnon(page)) {
swp_entry_t entry = { .val = page_private(subpage) };
pte_t swp_pte;
+
+ VM_BUG_ON(!pvmw.pte);
/*
* Store the swap location in the pte.
* See handle_pte_fault() ...
@@ -1808,7 +1884,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
*
* See Documentation/vm/mmu_notifier.rst
*/
- page_remove_rmap(subpage, compound_order(page));
+ page_remove_rmap(subpage, map_order);
put_page(page);
}

--
2.28.0
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