Messages in this thread | | | Date | Thu, 1 Aug 2019 14:43:52 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v2 1/2] khugepaged: enable collapse pmd for pte-mapped THP |
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On 07/31, Song Liu wrote: > > +void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long haddr) > +{ > + struct vm_area_struct *vma = find_vma(mm, haddr); > + pmd_t *pmd = mm_find_pmd(mm, haddr); > + struct page *hpage = NULL; > + unsigned long addr; > + spinlock_t *ptl; > + int count = 0; > + pmd_t _pmd; > + int i; > + > + VM_BUG_ON(haddr & ~HPAGE_PMD_MASK); > + > + if (!vma || !pmd || pmd_trans_huge(*pmd)) ^^^^^^^^^^^^^^^^^^^^
mm_find_pmd() returns NULL if pmd_trans_huge()
> + /* step 1: check all mapped PTEs are to the right huge page */ > + for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) { > + pte_t *pte = pte_offset_map(pmd, addr); > + struct page *page; > + > + if (pte_none(*pte)) > + continue; > + > + page = vm_normal_page(vma, addr, *pte); > + > + if (!PageCompound(page)) > + return; > + > + if (!hpage) { > + hpage = compound_head(page); > + if (hpage->mapping != vma->vm_file->f_mapping)
Hmm. But how can we know this is still the same vma ?
If nothing else, why vma->vm_file can't be NULL?
Say, a process unmaps this memory after khugepaged_add_pte_mapped_thp() was called, then it does mmap(haddr, MAP_PRIVATE|MAP_ANONYMOUS), then do_huge_pmd_anonymous_page() installs a huge page at the same address, then split_huge_pmd() is called by any reason.
No?
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