Re: [PATCH v1 1/2] mm: thp: move pmd check inside ptl for freeze_page()

[Kirill A. Shutemov]

On Mon, Jun 20, 2016 at 12:32:01PM +0300, Kirill A. Shutemov wrote:
> > +void split_huge_pmd_address_freeze(struct vm_area_struct *vma,
> > +                           unsigned long address, struct page *page)
> > +{
> > +   pgd_t *pgd;
> > +   pud_t *pud;
> > +   pmd_t *pmd;
> > +
> > +   pgd = pgd_offset(vma->vm_mm, address);
> > +   if (!pgd_present(*pgd))
> > +           return;
> > +
> > +   pud = pud_offset(pgd, address);
> > +   if (!pud_present(*pud))
> > +           return;
> > +
> > +   pmd = pmd_offset(pud, address);
> > +   __split_huge_pmd(vma, pmd, address, page, true);
> >  }
> 
> I don't see a reason to introduce new function. Just move the page
> check under ptl from split_huge_pmd_address() and that should be enough.
> 
> Or am I missing something?

I'm talking about something like patch below. Could you test it?

If it works fine to you, feel free to submit with my Signed-off-by.

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index eb810816bbc6..92ce91c03cd0 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -98,7 +98,7 @@ static inline int split_huge_page(struct page *page)
 void deferred_split_huge_page(struct page *page);
 
 void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
-               unsigned long address, bool freeze);
+               unsigned long address, bool freeze, struct page *page);
 
 #define split_huge_pmd(__vma, __pmd, __address)                                
\
        do {                                                            \
@@ -106,7 +106,7 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t 
*pmd,
                if (pmd_trans_huge(*____pmd)                            \
                                        || pmd_devmap(*____pmd))        \
                        __split_huge_pmd(__vma, __pmd, __address,       \
-                                               false);                 \
+                                               false, NULL);           \
        }  while (0)
 
 
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index eaf3a4a655a6..2297aa41581e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1638,7 +1638,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct 
*vma, pmd_t *pmd,
 }
 
 void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
-               unsigned long address, bool freeze)
+               unsigned long address, bool freeze, struct page *page)
 {
        spinlock_t *ptl;
        struct mm_struct *mm = vma->vm_mm;
@@ -1646,8 +1646,17 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t 
*pmd,
 
        mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE);
        ptl = pmd_lock(mm, pmd);
+
+       /*
+        * If caller asks to setup a migration entries, we need a page to check
+        * pmd against. Otherwise we can end up replacing wrong page.
+        */
+       VM_BUG_ON(freeze && !page);
+       if (page && page != pmd_page(*pmd))
+               goto out;
+
        if (pmd_trans_huge(*pmd)) {
-               struct page *page = pmd_page(*pmd);
+               page = pmd_page(*pmd);
                if (PageMlocked(page))
                        clear_page_mlock(page);
        } else if (!pmd_devmap(*pmd))
@@ -1678,20 +1687,12 @@ void split_huge_pmd_address(struct vm_area_struct *vma, 
unsigned long address,
                return;
 
        /*
-        * If caller asks to setup a migration entries, we need a page to check
-        * pmd against. Otherwise we can end up replacing wrong page.
-        */
-       VM_BUG_ON(freeze && !page);
-       if (page && page != pmd_page(*pmd))
-               return;
-
-       /*
         * Caller holds the mmap_sem write mode or the anon_vma lock,
         * so a huge pmd cannot materialize from under us (khugepaged
         * holds both the mmap_sem write mode and the anon_vma lock
         * write mode).
         */
-       __split_huge_pmd(vma, pmd, address, freeze);
+       __split_huge_pmd(vma, pmd, address, freeze, page);
 }
 
 void vma_adjust_trans_huge(struct vm_area_struct *vma,
-- 
 Kirill A. Shutemov