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Message-ID: <86e8c75b-1717-4335-9a1f-c663192dbf84@linux.alibaba.com>
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.
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