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Message-Id: <20240911065600.1002644-3-dev.jain@arm.com>
Date: Wed, 11 Sep 2024 12:26:00 +0530
From: Dev Jain <dev.jain@....com>
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Dev Jain <dev.jain@....com>
Subject: [PATCH v3 2/2] mm: Allocate THP on hugezeropage wp-fault
Introduce do_huge_zero_wp_pmd() to handle wp-fault on a hugezeropage and
replace it with a PMD-mapped THP. Change the helper introduced in the
previous patch to flush TLB entry corresponding to the hugezeropage.
In case of failure, fallback to splitting the PMD.
Signed-off-by: Dev Jain <dev.jain@....com>
---
mm/huge_memory.c | 52 +++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 49 insertions(+), 3 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b96a1ff2bf40..3e28946a805f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -987,16 +987,20 @@ static void __pmd_thp_fault_success_stats(struct vm_area_struct *vma)
static void map_pmd_thp(struct folio *folio, struct vm_fault *vmf,
struct vm_area_struct *vma, unsigned long haddr)
{
- pmd_t entry;
+ pmd_t entry, old_pmd;
+ bool is_pmd_none = pmd_none(*vmf->pmd);
entry = mk_huge_pmd(&folio->page, vma->vm_page_prot);
entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
folio_add_new_anon_rmap(folio, vma, haddr, RMAP_EXCLUSIVE);
folio_add_lru_vma(folio, vma);
+ if (!is_pmd_none)
+ old_pmd = pmdp_huge_clear_flush(vma, haddr, vmf->pmd);
set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
- mm_inc_nr_ptes(vma->vm_mm);
+ if (is_pmd_none)
+ mm_inc_nr_ptes(vma->vm_mm);
}
static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf)
@@ -1576,6 +1580,41 @@ void huge_pmd_set_accessed(struct vm_fault *vmf)
spin_unlock(vmf->ptl);
}
+static vm_fault_t do_huge_zero_wp_pmd(struct vm_fault *vmf, unsigned long haddr)
+{
+ struct vm_area_struct *vma = vmf->vma;
+ gfp_t gfp = vma_thp_gfp_mask(vma);
+ struct mmu_notifier_range range;
+ struct folio *folio;
+ vm_fault_t ret = 0;
+
+ folio = pmd_thp_fault_alloc(gfp, vma, haddr, vmf->address);
+ if (unlikely(!folio)) {
+ ret = VM_FAULT_FALLBACK;
+ goto out;
+ }
+
+ mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma->vm_mm, haddr,
+ haddr + HPAGE_PMD_SIZE);
+ mmu_notifier_invalidate_range_start(&range);
+ vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
+ if (unlikely(!pmd_same(pmdp_get(vmf->pmd), vmf->orig_pmd)))
+ goto release;
+ ret = check_stable_address_space(vma->vm_mm);
+ if (ret)
+ goto release;
+ map_pmd_thp(folio, vmf, vma, haddr);
+ __pmd_thp_fault_success_stats(vma);
+ goto unlock;
+release:
+ folio_put(folio);
+unlock:
+ spin_unlock(vmf->ptl);
+ mmu_notifier_invalidate_range_end(&range);
+out:
+ return ret;
+}
+
vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf)
{
const bool unshare = vmf->flags & FAULT_FLAG_UNSHARE;
@@ -1588,8 +1627,15 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf)
vmf->ptl = pmd_lockptr(vma->vm_mm, vmf->pmd);
VM_BUG_ON_VMA(!vma->anon_vma, vma);
- if (is_huge_zero_pmd(orig_pmd))
+ if (is_huge_zero_pmd(orig_pmd)) {
+ vm_fault_t ret = do_huge_zero_wp_pmd(vmf, haddr);
+
+ if (!(ret & VM_FAULT_FALLBACK))
+ return ret;
+
+ /* Fallback to splitting PMD if THP cannot be allocated */
goto fallback;
+ }
spin_lock(vmf->ptl);
--
2.30.2
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