> On Aug 1, 2019, at 5:43 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>
> 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()
Good catch! I will simplify this one in v3.
>
>> + /* 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?
Good point. We should confirm vma->vm_file is not NULL.
Thanks,
Song
