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?
> Of course, there is no code that sets both flags.
and of course, nobody should ever pass both FOLL_SPLIT and FOLL_SPLIT_PMD,
perhaps this deserves a warning.
Not to mention that it would be nice to kill FOLL_SPLIT which has a single
user, but this is another story.
Oleg.
