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Message-ID: <9411b518-2505-40ca-bd81-7127dc638521@arm.com>
Date: Thu, 5 Sep 2024 14:22:21 +0530
From: Dev Jain <dev.jain@....com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: akpm@...ux-foundation.org, david@...hat.com, willy@...radead.org,
ryan.roberts@....com, anshuman.khandual@....com, catalin.marinas@....com,
cl@...two.org, vbabka@...e.cz, mhocko@...e.com, apopple@...dia.com,
dave.hansen@...ux.intel.com, will@...nel.org, baohua@...nel.org,
jack@...e.cz, mark.rutland@....com, hughd@...gle.com,
aneesh.kumar@...nel.org, yang@...amperecomputing.com, peterx@...hat.com,
ioworker0@...il.com, jglisse@...gle.com,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [PATCH v2 2/2] mm: Allocate THP on hugezeropage wp-fault
On 9/5/24 13:56, Kirill A. Shutemov wrote:
> On Wed, Sep 04, 2024 at 03:39:23PM +0530, Dev Jain wrote:
>> Introduce do_huge_zero_wp_pmd() to handle wp-fault on a hugezeropage and
>> replace it with a PMD-mapped THP. Change the helpers introduced in the
>> previous patch to flush TLB entry corresponding to the hugezeropage,
>> and preserve PMD uffd-wp marker. In case of failure, fallback to
>> splitting the PMD.
>>
>> Signed-off-by: Dev Jain <dev.jain@....com>
>> ---
>> include/linux/huge_mm.h | 6 ++++
>> mm/huge_memory.c | 79 +++++++++++++++++++++++++++++++++++------
>> mm/memory.c | 5 +--
>> 3 files changed, 78 insertions(+), 12 deletions(-)
>>
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index e25d9ebfdf89..fdd2cf473a3c 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -9,6 +9,12 @@
>> #include <linux/kobject.h>
>>
>> vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf);
>> +vm_fault_t thp_fault_alloc(gfp_t gfp, int order, struct vm_area_struct *vma,
>> + unsigned long haddr, struct folio **foliop,
>> + unsigned long addr);
>> +void map_pmd_thp(struct folio *folio, struct vm_fault *vmf,
>> + struct vm_area_struct *vma, unsigned long haddr,
>> + pgtable_t pgtable);
> Why? I don't see users outside huge_memory.c.
Ah sorry! When I started out on this I may have planned to use
it in mm/memory.c, but then completely forgot to drop this.
>
>> int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
>> pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
>> struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma);
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 58125fbcc532..150163ad77d3 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -943,9 +943,9 @@ unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr,
>> }
>> EXPORT_SYMBOL_GPL(thp_get_unmapped_area);
>>
>> -static vm_fault_t thp_fault_alloc(gfp_t gfp, int order, struct vm_area_struct *vma,
>> - unsigned long haddr, struct folio **foliop,
>> - unsigned long addr)
>> +vm_fault_t thp_fault_alloc(gfp_t gfp, int order, struct vm_area_struct *vma,
>> + unsigned long haddr, struct folio **foliop,
>> + unsigned long addr)
>> {
>> struct folio *folio = vma_alloc_folio(gfp, order, vma, haddr, true);
>>
>> @@ -984,21 +984,29 @@ static void __thp_fault_success_stats(struct vm_area_struct *vma, int order)
>> count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC);
>> }
>>
>> -static void map_pmd_thp(struct folio *folio, struct vm_fault *vmf,
>> - struct vm_area_struct *vma, unsigned long haddr,
>> - pgtable_t pgtable)
>> +void map_pmd_thp(struct folio *folio, struct vm_fault *vmf,
>> + struct vm_area_struct *vma, unsigned long haddr,
>> + pgtable_t pgtable)
>> {
>> - 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);
>> - pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
>> + if (!is_pmd_none) {
>> + old_pmd = pmdp_huge_clear_flush(vma, haddr, vmf->pmd);
>> + if (pmd_uffd_wp(old_pmd))
>> + entry = pmd_mkuffd_wp(entry);
>> + }
>> + if (pgtable)
>> + pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
>> 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 +1584,50 @@ void huge_pmd_set_accessed(struct vm_fault *vmf)
>> spin_unlock(vmf->ptl);
>> }
>>
>> +static vm_fault_t do_huge_zero_wp_pmd_locked(struct vm_fault *vmf,
>> + unsigned long haddr,
>> + struct folio *folio)
> Why the helper is needed? Cannot it be just opencodded in
> do_huge_zero_wp_pmd()?
I was taking inspiration from split_huge_pud_locked() and the like.
Although I guess I should open code it, since do_huge_zero_wp_pmd_locked()
is small anyways.
>
>> +{
>> + struct vm_area_struct *vma = vmf->vma;
>> + vm_fault_t ret = 0;
>> +
>> + ret = check_stable_address_space(vma->vm_mm);
>> + if (ret)
>> + goto out;
>> + map_pmd_thp(folio, vmf, vma, haddr, NULL);
>> +out:
>> + return ret;
>> +}
>> +
>> +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 = NULL;
>> + vm_fault_t ret = 0;
>> +
>> + ret = thp_fault_alloc(gfp, HPAGE_PMD_ORDER, vma, haddr, &folio,
>> + vmf->address);
>> + if (ret)
>> + 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 unlock;
>> + ret = do_huge_zero_wp_pmd_locked(vmf, haddr, folio);
>> + if (!ret)
>> + __thp_fault_success_stats(vma, HPAGE_PMD_ORDER);
>> +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 +1640,15 @@ 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);
>>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index 3c01d68065be..c081a25f5173 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -5409,9 +5409,10 @@ static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf)
>> if (vma_is_anonymous(vma)) {
>> if (likely(!unshare) &&
>> userfaultfd_huge_pmd_wp(vma, vmf->orig_pmd)) {
>> - if (userfaultfd_wp_async(vmf->vma))
>> + if (!userfaultfd_wp_async(vmf->vma))
>> + return handle_userfault(vmf, VM_UFFD_WP);
>> + if (!is_huge_zero_pmd(vmf->orig_pmd))
>> goto split;
>> - return handle_userfault(vmf, VM_UFFD_WP);
>> }
>> return do_huge_pmd_wp_page(vmf);
>> }
>> --
>> 2.30.2
>>
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