linux-kernel - Re: [PATCH v5 1/6] mm: memory: extend finish

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Date: Thu, 13 Jun 2024 08:51:43 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Kefeng Wang <wangkefeng.wang@...wei.com>, akpm@...ux-foundation.org,
 hughd@...gle.com
Cc: willy@...radead.org, david@...hat.com, ying.huang@...el.com,
 21cnbao@...il.com, ryan.roberts@....com, shy828301@...il.com,
 ziy@...dia.com, ioworker0@...il.com, da.gomez@...sung.com,
 p.raghav@...sung.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/6] mm: memory: extend finish_fault() to support large
 folio



On 2024/6/12 21:40, Kefeng Wang wrote:
> 
> 
> On 2024/6/11 18:11, Baolin Wang wrote:
>> Add large folio mapping establishment support for finish_fault() as a
>> preparation, to support multi-size THP allocation of anonymous shmem 
>> pages
>> in the following patches.
>>
>> Keep the same behavior (per-page fault) for non-anon shmem to avoid 
>> inflating
>> the RSS unintentionally, and we can discuss what size of mapping to build
>> when extending mTHP to control non-anon shmem in the future.
>>
>> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
>> ---
>>   mm/memory.c | 57 +++++++++++++++++++++++++++++++++++++++++++----------
>>   1 file changed, 47 insertions(+), 10 deletions(-)
>>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index eef4e482c0c2..72775ee99ff3 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -4831,9 +4831,12 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
>>   {
>>       struct vm_area_struct *vma = vmf->vma;
>>       struct page *page;
>> +    struct folio *folio;
>>       vm_fault_t ret;
>>       bool is_cow = (vmf->flags & FAULT_FLAG_WRITE) &&
>>                 !(vma->vm_flags & VM_SHARED);
>> +    int type, nr_pages;
>> +    unsigned long addr = vmf->address;
>>       /* Did we COW the page? */
>>       if (is_cow)
>> @@ -4864,24 +4867,58 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
>>               return VM_FAULT_OOM;
>>       }
>> +    folio = page_folio(page);
>> +    nr_pages = folio_nr_pages(folio);
>> +
>> +    /*
>> +     * Using per-page fault to maintain the uffd semantics, and same
>> +     * approach also applies to non-anonymous-shmem faults to avoid
>> +     * inflating the RSS of the process.
>> +     */
>> +    if (!vma_is_anon_shmem(vma) || unlikely(userfaultfd_armed(vma))) {
>> +        nr_pages = 1;
>> +    } else if (nr_pages > 1) {
>> +        pgoff_t idx = folio_page_idx(folio, page);
>> +        /* The page offset of vmf->address within the VMA. */
>> +        pgoff_t vma_off = vmf->pgoff - vmf->vma->vm_pgoff;
>> +
>                          vma->vm_pgoff
> 
>> +        /*
>> +         * Fallback to per-page fault in case the folio size in page
>> +         * cache beyond the VMA limits.
>> +         */
>> +        if (unlikely(vma_off < idx ||
>> +                 vma_off + (nr_pages - idx) > vma_pages(vma))) {
>> +            nr_pages = 1;
>> +        } else {
>> +            /* Now we can set mappings for the whole large folio. */
>> +            addr = vmf->address - idx * PAGE_SIZE;
> 
>              addr -= idx * PAGE_SIZE;
> 
>> +            page = &folio->page;
>> +        }
>> +    }
>> +
>>       vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
>> -                      vmf->address, &vmf->ptl);
>> +                       addr, &vmf->ptl);
> 
> no newline now,
> 
>>       if (!vmf->pte)
>>           return VM_FAULT_NOPAGE;
>>       /* Re-check under ptl */
>> -    if (likely(!vmf_pte_changed(vmf))) {
>> -        struct folio *folio = page_folio(page);
>> -        int type = is_cow ? MM_ANONPAGES : mm_counter_file(folio);
>> -
>> -        set_pte_range(vmf, folio, page, 1, vmf->address);
>> -        add_mm_counter(vma->vm_mm, type, 1);
>> -        ret = 0;
>> -    } else {
>> -        update_mmu_tlb(vma, vmf->address, vmf->pte);
>> +    if (nr_pages == 1 && unlikely(vmf_pte_changed(vmf))) {
>> +        update_mmu_tlb(vma, addr, vmf->pte);
>> +        ret = VM_FAULT_NOPAGE;
>> +        goto unlock;
>> +    } else if (nr_pages > 1 && !pte_range_none(vmf->pte, nr_pages)) {
>> +        update_mmu_tlb_range(vma, addr, vmf->pte, nr_pages);
>>           ret = VM_FAULT_NOPAGE;
>> +        goto unlock;
>>       }
> 
> We may add a vmf_pte_range_changed(), but separate it.
> 
> Some very small nits, up to you,
> 
> Reviewed-by: Kefeng Wang <wangkefeng.wang@...wei.com>

Thanks for reviewing. If a new version is needed, then I will clean up 
these coding style issues.