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SubjectRe: [PATCH 2/6] thp: optimize away unnecessary page table locking
Hi Hillf,

(1/13/2012 7:04), Hillf Danton wrote:
[...]
>> +/*
>> + * Returns 1 if a given pmd is mapping a thp and stable (not under splitting.)
>> + * Returns 0 otherwise. Note that if it returns 1, this routine returns without
>> + * unlocking page table locks. So callers must unlock them.
>> + */
>> +int pmd_trans_huge_stable(pmd_t *pmd, struct vm_area_struct *vma)
>> +{
>> + VM_BUG_ON(!rwsem_is_locked(&vma->vm_mm->mmap_sem));
>> +
>> + if (!pmd_trans_huge(*pmd))
>> + return 0;
>> +
>> + spin_lock(&vma->vm_mm->page_table_lock);
>> + if (likely(pmd_trans_huge(*pmd))) {
>> + if (pmd_trans_splitting(*pmd)) {
>> + spin_unlock(&vma->vm_mm->page_table_lock);
>> + wait_split_huge_page(vma->anon_vma, pmd);
>> + return 0;
>> + } else {
>
> spin_unlock(&vma->vm_mm->page_table_lock); yes?

No. Unlocking is supposed to be done by the caller as commented.

Thanks,
Naoya

>
>> + /* Thp mapped by 'pmd' is stable, so we can
>> + * handle it as it is. */
>> + return 1;
>> + }
>> + }
>> + spin_unlock(&vma->vm_mm->page_table_lock);
>> + return 0;
>> +}
>> +



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