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Thu, 4 Sep 2025 09:05:33 +0800 Content-Type: multipart/alternative; boundary="------------A492Ru4Vmeb1KvsDwdS9HbYp" Message-ID: Date: Thu, 4 Sep 2025 09:05:32 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] filemap: optimize order0 folio in filemap_map_pages To: David Hildenbrand , , , CC: References: <20250903084223.1653192-1-tujinjiang@huawei.com> <3c283054-b14e-4f36-966f-78cf3bc0f3af@redhat.com> From: Jinjiang Tu In-Reply-To: <3c283054-b14e-4f36-966f-78cf3bc0f3af@redhat.com> X-Originating-IP: [10.174.178.49] X-ClientProxiedBy: kwepems200002.china.huawei.com (7.221.188.68) To kwepemr500001.china.huawei.com (7.202.194.229) X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: E5DE640013 X-Stat-Signature: 8u7x9b9pbwoqtidb3gnpqwmutom3taua X-HE-Tag: 1756947959-378747 X-HE-Meta: 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 +293Tnqc KE3+2QfS+VcV+9uraFkiU6P7AWkS+1P+7UrqeiGDjuPFLc3S0K4MktpwkQNJQmb8W1I0Z/GW+CaIfjOH4NVehCBckl6JmvWBHqs4PXT7uPF214AJs+ra0t/3+PHJMupGmvbj7jL15C1DWXZF+6HICgy49oKJ/YRLnwuuL4Es36/1qy+wWPjPMNeYuX1Qp+t2sYSsUgvH1FoMeiw8awj/iYP5kBfYa934Hccw9seOE6YFN1RKVxNDEbJQs9zmkeNuKHfB75cVF/VVdQb/qFAeJoI0QxU/DryJGVx3Og7yB0tOCW8VBL2DqZ3ePsq+V0F91ADAw+sK2mjRVzs/L05nMIMiMm0zXBVQw8zdJWiOkprwWLWlhMnlV3hJHJKjSXXAaJpFFufF23zIDABh4hUq8VsneuwJXeXpgZMS6 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: --------------A492Ru4Vmeb1KvsDwdS9HbYp Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit 在 2025/9/3 17:16, David Hildenbrand 写道: >> +++ b/mm/filemap.c >> @@ -3693,6 +3693,7 @@ static vm_fault_t >> filemap_map_folio_range(struct vm_fault *vmf, >>       } >>         vmf->pte = old_ptep; >> +    folio_put(folio); >>         return ret; >>   } >> @@ -3705,7 +3706,7 @@ static vm_fault_t >> filemap_map_order0_folio(struct vm_fault *vmf, >>       struct page *page = &folio->page; >>         if (PageHWPoison(page)) >> -        return ret; >> +        goto out; >>         /* See comment of filemap_map_folio_range() */ >>       if (!folio_test_workingset(folio)) >> @@ -3717,15 +3718,17 @@ static vm_fault_t >> filemap_map_order0_folio(struct vm_fault *vmf, >>        * the fault-around logic. >>        */ >>       if (!pte_none(ptep_get(vmf->pte))) >> -        return ret; >> +        goto out; >>         if (vmf->address == addr) >>           ret = VM_FAULT_NOPAGE; >>         set_pte_range(vmf, folio, page, 1, addr); >>       (*rss)++; >> -    folio_ref_inc(folio); >> +    return ret; >>   +out: >> +    folio_put(folio); > > We can use a folio_ref_dec() here > >     /* Locked folios cannot get truncated. */ >     folio_ref_dec(folio); > >>       return ret; >>   } >>   @@ -3785,7 +3788,6 @@ vm_fault_t filemap_map_pages(struct vm_fault >> *vmf, >>                       nr_pages, &rss, &mmap_miss); >>             folio_unlock(folio); >> -        folio_put(folio); >>       } while ((folio = next_uptodate_folio(&xas, mapping, >> end_pgoff)) != NULL); >>       add_mm_counter(vma->vm_mm, folio_type, rss); >>       pte_unmap_unlock(vmf->pte, vmf->ptl); > > > I think we can optimize filemap_map_folio_range() as well: > > diff --git a/mm/filemap.c b/mm/filemap.c > index b101405b770ae..d1fcddc72c5f6 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -3646,6 +3646,7 @@ static vm_fault_t filemap_map_folio_range(struct > vm_fault *vmf, >                         unsigned long addr, unsigned int nr_pages, >                         unsigned long *rss, unsigned short *mmap_miss) >  { > +       bool ref_from_caller = true; >         vm_fault_t ret = 0; >         struct page *page = folio_page(folio, start); >         unsigned int count = 0; > @@ -3679,7 +3680,9 @@ static vm_fault_t filemap_map_folio_range(struct > vm_fault *vmf, >                 if (count) { >                         set_pte_range(vmf, folio, page, count, addr); >                         *rss += count; > -                       folio_ref_add(folio, count); > +                       if (count - ref_from_caller) > +                               folio_ref_add(folio, count - > ref_from_caller); > +                       ref_from_caller = false; >                         if (in_range(vmf->address, addr, count * > PAGE_SIZE)) >                                 ret = VM_FAULT_NOPAGE; >                 } > @@ -3694,13 +3697,19 @@ static vm_fault_t > filemap_map_folio_range(struct vm_fault *vmf, >         if (count) { >                 set_pte_range(vmf, folio, page, count, addr); >                 *rss += count; > -               folio_ref_add(folio, count); > +               if (count - ref_from_caller) > +                       folio_ref_add(folio, count - ref_from_caller); > +               ref_from_caller = false; >                 if (in_range(vmf->address, addr, count * PAGE_SIZE)) >                         ret = VM_FAULT_NOPAGE; >         } > >         vmf->pte = old_ptep; > > +       if (ref_from_caller) > +               /* Locked folios cannot get truncated. */ > +               folio_ref_dec(folio); > + >         return ret; >  } > > > It would save at least a folio_ref_dec(), and in corner cases (only > map a single page) > also a folio_ref_add(). > Maybe We can first count the refcount to add, and only call folio_ref_{add, sub} once before return --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3643,6 +3643,7 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,         struct page *page = folio_page(folio, start);         unsigned int count = 0;         pte_t *old_ptep = vmf->pte; +       int ref_to_add = -1;         do {                 if (PageHWPoison(page + count)) @@ -3672,7 +3673,7 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,                 if (count) {                         set_pte_range(vmf, folio, page, count, addr);                         *rss += count; -                       folio_ref_add(folio, count); +                       ref_to_add += count;                         if (in_range(vmf->address, addr, count * PAGE_SIZE))                                 ret = VM_FAULT_NOPAGE;                 } @@ -3687,12 +3688,17 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,         if (count) {                 set_pte_range(vmf, folio, page, count, addr);                 *rss += count; -               folio_ref_add(folio, count); +               ref_to_add += count;                 if (in_range(vmf->address, addr, count * PAGE_SIZE))                         ret = VM_FAULT_NOPAGE;         }         vmf->pte = old_ptep; +       /* Locked folios cannot get truncated. */ +       if (ref_to_add > 0) +               folio_ref_add(folio, ref_to_add); +       else if (ref_to_add < 0) +               folio_ref_sub(folio, ref_to_add);         return ret;  } --------------A492Ru4Vmeb1KvsDwdS9HbYp Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: 8bit


在 2025/9/3 17:16, David Hildenbrand 写道:
+++ b/mm/filemap.c
@@ -3693,6 +3693,7 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
      }
        vmf->pte = old_ptep;
+    folio_put(folio);
        return ret;
  }
@@ -3705,7 +3706,7 @@ static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
      struct page *page = &folio->page;
        if (PageHWPoison(page))
-        return ret;
+        goto out;
        /* See comment of filemap_map_folio_range() */
      if (!folio_test_workingset(folio))
@@ -3717,15 +3718,17 @@ static vm_fault_t filemap_map_order0_folio(struct vm_fault *vmf,
       * the fault-around logic.
       */
      if (!pte_none(ptep_get(vmf->pte)))
-        return ret;
+        goto out;
        if (vmf->address == addr)
          ret = VM_FAULT_NOPAGE;
        set_pte_range(vmf, folio, page, 1, addr);
      (*rss)++;
-    folio_ref_inc(folio);
+    return ret;
  +out:
+    folio_put(folio);

We can use a folio_ref_dec() here

    /* Locked folios cannot get truncated. */
    folio_ref_dec(folio);

      return ret;
  }
  @@ -3785,7 +3788,6 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
                      nr_pages, &rss, &mmap_miss);
            folio_unlock(folio);
-        folio_put(folio);
      } while ((folio = next_uptodate_folio(&xas, mapping, end_pgoff)) != NULL);
      add_mm_counter(vma->vm_mm, folio_type, rss);
      pte_unmap_unlock(vmf->pte, vmf->ptl);


I think we can optimize filemap_map_folio_range() as well:

diff --git a/mm/filemap.c b/mm/filemap.c
index b101405b770ae..d1fcddc72c5f6 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3646,6 +3646,7 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
                        unsigned long addr, unsigned int nr_pages,
                        unsigned long *rss, unsigned short *mmap_miss)
 {
+       bool ref_from_caller = true;
        vm_fault_t ret = 0;
        struct page *page = folio_page(folio, start);
        unsigned int count = 0;
@@ -3679,7 +3680,9 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
                if (count) {
                        set_pte_range(vmf, folio, page, count, addr);
                        *rss += count;
-                       folio_ref_add(folio, count);
+                       if (count - ref_from_caller)
+                               folio_ref_add(folio, count - ref_from_caller);
+                       ref_from_caller = false;
                        if (in_range(vmf->address, addr, count * PAGE_SIZE))
                                ret = VM_FAULT_NOPAGE;
                }
@@ -3694,13 +3697,19 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
        if (count) {
                set_pte_range(vmf, folio, page, count, addr);
                *rss += count;
-               folio_ref_add(folio, count);
+               if (count - ref_from_caller)
+                       folio_ref_add(folio, count - ref_from_caller);
+               ref_from_caller = false;
                if (in_range(vmf->address, addr, count * PAGE_SIZE))
                        ret = VM_FAULT_NOPAGE;
        }
 
        vmf->pte = old_ptep;
 
+       if (ref_from_caller)
+               /* Locked folios cannot get truncated. */
+               folio_ref_dec(folio);
+
        return ret;
 }


It would save at least a folio_ref_dec(), and in corner cases (only map a single page)
also a folio_ref_add(). 

Maybe We can first count the refcount to add, and only call folio_ref_{add, sub} once before return


--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3643,6 +3643,7 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
        struct page *page = folio_page(folio, start);
        unsigned int count = 0;
        pte_t *old_ptep = vmf->pte;
+       int ref_to_add = -1;
 
        do {
                if (PageHWPoison(page + count))
@@ -3672,7 +3673,7 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
                if (count) {
                        set_pte_range(vmf, folio, page, count, addr);
                        *rss += count;
-                       folio_ref_add(folio, count);
+                       ref_to_add += count;
                        if (in_range(vmf->address, addr, count * PAGE_SIZE))
                                ret = VM_FAULT_NOPAGE;
                }
@@ -3687,12 +3688,17 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf,
        if (count) {
                set_pte_range(vmf, folio, page, count, addr);
                *rss += count;
-               folio_ref_add(folio, count);
+               ref_to_add += count;
                if (in_range(vmf->address, addr, count * PAGE_SIZE))
                        ret = VM_FAULT_NOPAGE;
        }
 
        vmf->pte = old_ptep;
+       /* Locked folios cannot get truncated. */
+       if (ref_to_add > 0)
+               folio_ref_add(folio, ref_to_add);
+       else if (ref_to_add < 0)
+               folio_ref_sub(folio, ref_to_add);
 
        return ret;
 }


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