| Message ID | 59fd15dd-4d39-5ec-2043-1d5117f7f85@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: allow pte_offset_map[_lock]() to fail | expand |
On Thu, Jun 8, 2023 at 6:40 PM Hugh Dickins <hughd@google.com> wrote: > > There is now no reason for follow_pmd_mask()'s FOLL_SPLIT_PMD block to > distinguish huge_zero_page from a normal THP: follow_page_pte() handles > any instability, and here it's a good idea to replace any pmd_none(*pmd) > by a page table a.s.a.p, in the huge_zero_page case as for a normal THP; > and this removes an unnecessary possibility of -EBUSY failure. > > (Hmm, couldn't the normal THP case have hit an unstably refaulted THP > before? But there are only two, exceptional, users of FOLL_SPLIT_PMD.) > > Signed-off-by: Hugh Dickins <hughd@google.com> Reviewed-by: Yang Shi <shy828301@gmail.com> > --- > mm/gup.c | 19 ++++--------------- > 1 file changed, 4 insertions(+), 15 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index bb67193c5460..4ad50a59897f 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -681,21 +681,10 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma, > return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap); > } > if (flags & FOLL_SPLIT_PMD) { > - int ret; > - page = pmd_page(*pmd); > - if (is_huge_zero_page(page)) { > - spin_unlock(ptl); > - ret = 0; > - split_huge_pmd(vma, pmd, address); > - if (pmd_trans_unstable(pmd)) > - ret = -EBUSY; > - } else { > - spin_unlock(ptl); > - split_huge_pmd(vma, pmd, address); > - ret = pte_alloc(mm, pmd) ? -ENOMEM : 0; > - } > - > - return ret ? ERR_PTR(ret) : > + spin_unlock(ptl); > + split_huge_pmd(vma, pmd, address); > + /* If pmd was left empty, stuff a page table in there quickly */ > + return pte_alloc(mm, pmd) ? ERR_PTR(-ENOMEM) : > follow_page_pte(vma, address, pmd, flags, &ctx->pgmap); > } > page = follow_trans_huge_pmd(vma, address, pmd, flags); > -- > 2.35.3 >
diff --git a/mm/gup.c b/mm/gup.c index bb67193c5460..4ad50a59897f 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -681,21 +681,10 @@ static struct page *follow_pmd_mask(struct vm_area_struct *vma, return follow_page_pte(vma, address, pmd, flags, &ctx->pgmap); } if (flags & FOLL_SPLIT_PMD) { - int ret; - page = pmd_page(*pmd); - if (is_huge_zero_page(page)) { - spin_unlock(ptl); - ret = 0; - split_huge_pmd(vma, pmd, address); - if (pmd_trans_unstable(pmd)) - ret = -EBUSY; - } else { - spin_unlock(ptl); - split_huge_pmd(vma, pmd, address); - ret = pte_alloc(mm, pmd) ? -ENOMEM : 0; - } - - return ret ? ERR_PTR(ret) : + spin_unlock(ptl); + split_huge_pmd(vma, pmd, address); + /* If pmd was left empty, stuff a page table in there quickly */ + return pte_alloc(mm, pmd) ? ERR_PTR(-ENOMEM) : follow_page_pte(vma, address, pmd, flags, &ctx->pgmap); } page = follow_trans_huge_pmd(vma, address, pmd, flags);
There is now no reason for follow_pmd_mask()'s FOLL_SPLIT_PMD block to distinguish huge_zero_page from a normal THP: follow_page_pte() handles any instability, and here it's a good idea to replace any pmd_none(*pmd) by a page table a.s.a.p, in the huge_zero_page case as for a normal THP; and this removes an unnecessary possibility of -EBUSY failure. (Hmm, couldn't the normal THP case have hit an unstably refaulted THP before? But there are only two, exceptional, users of FOLL_SPLIT_PMD.) Signed-off-by: Hugh Dickins <hughd@google.com> --- mm/gup.c | 19 ++++--------------- 1 file changed, 4 insertions(+), 15 deletions(-)