On 08/08, Song Liu wrote: > > > On Aug 8, 2019, at 9:37 AM, Oleg Nesterov <[email protected]> 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.
