> On Aug 9, 2019, at 9:35 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>
> On 08/08, Song Liu wrote:
>>
>>> On Aug 8, 2019, at 9:37 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>>>
>>> On 08/07, Song Liu wrote:
>>>>
>>>> @@ -399,7 +399,7 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
>>>> spin_unlock(ptl);
>>>> return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap);
>>>> }
>>>> - if (flags & FOLL_SPLIT) {
>>>> + if (flags & (FOLL_SPLIT | FOLL_SPLIT_PMD)) {
>>>> int ret;
>>>> page = pmd_page(*pmd);
>>>> if (is_huge_zero_page(page)) {
>>>> @@ -408,7 +408,7 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
>>>> split_huge_pmd(vma, pmd, address);
>>>> if (pmd_trans_unstable(pmd))
>>>> ret = -EBUSY;
>>>> - } else {
>>>> + } else if (flags & FOLL_SPLIT) {
>>>> if (unlikely(!try_get_page(page))) {
>>>> spin_unlock(ptl);
>>>> return ERR_PTR(-ENOMEM);
>>>> @@ -420,6 +420,10 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma,
>>>> put_page(page);
>>>> if (pmd_none(*pmd))
>>>> return no_page_table(vma, flags);
>>>> + } else { /* flags & FOLL_SPLIT_PMD */
>>>> + spin_unlock(ptl);
>>>> + split_huge_pmd(vma, pmd, address);
>>>> + ret = pte_alloc(mm, pmd) ? -ENOMEM : 0;
>>>> }
>>>
>>> Can't resist, let me repeat that I do not like this patch because imo
>>> it complicates this code for no reason.
>>
>> Personally, I don't think this is more complicated than your version.
>
> I do, but of course this is subjective.
>
>> Also, if some code calls follow_pmd_mask() with flags contains both
>> FOLL_SPLIT and FOLL_SPLIT_PMD, we should honor FOLL_SPLIT and split the
>> huge page.
>
> Heh. why not other way around?
Because FOLL_SPLIT splits both the page and the pmd. FOLL_SPLIT_PMD
only splits the pmd, so it is a subset of FOLL_SPLIT. When the user
sets both, we should split both the page and the pmd.
Thanks,
Song
