Re: [PATCH 05/11] mm: page_vma_mapped_walk(): prettify PVMW_MIGRATION block

Peter Xu
2021-06-10T14:48:38Z

On Wed, Jun 09, 2021 at 11:42:12PM -0700, Hugh Dickins wrote:
> page_vma_mapped_walk() cleanup: rearrange the !pmd_present() block to
> follow the same "return not_found, return not_found, return true" pattern
> as the block above it (note: returning not_found there is never premature,
> since existence or prior existence of huge pmd guarantees good alignment).
>
> Signed-off-by: Hugh Dickins <hughd@google.com>
> Cc: <stable@vger.kernel.org>
> ---
> mm/page_vma_mapped.c | 30 ++++++++++++++----------------
> 1 file changed, 14 insertions(+), 16 deletions(-)
>
> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
> index 81000dd0b5da..b96fae568bc2 100644
> --- a/mm/page_vma_mapped.c
> +++ b/mm/page_vma_mapped.c
> @@ -201,24 +201,22 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
> if (pmd_page(pmde) != page)
> return not_found(pvmw);
> return true;
> - } else if (!pmd_present(pmde)) {
> - if (thp_migration_supported()) {
> - if (!(pvmw->flags & PVMW_MIGRATION))
> - return not_found(pvmw);
> - if (is_migration_entry(pmd_to_swp_entry(pmde))) {
> - swp_entry_t entry = pmd_to_swp_entry(pmde);
> + }
> + if (!pmd_present(pmde)) {
> + swp_entry_t entry;
>
> - if (migration_entry_to_page(entry) != page)
> - return not_found(pvmw);
> - return true;
> - }
> - }
> - return not_found(pvmw);
> - } else {
> - /* THP pmd was split under us: handle on pte level */
> - spin_unlock(pvmw->ptl);
> - pvmw->ptl = NULL;
> + if (!thp_migration_supported() ||
> + !(pvmw->flags & PVMW_MIGRATION))
> + return not_found(pvmw);
> + entry = pmd_to_swp_entry(pmde);
> + if (!is_migration_entry(entry) ||
> + migration_entry_to_page(entry) != page)

We'll need to do s/migration_entry_to_page/pfn_swap_entry_to_page/, depending
on whether Alistair's series lands first or not I guess (as you mentioned in
the cover letter).

Thanks for the change, it does look much better.

Reviewed-by: Peter Xu <peterx@redhat.com>

> + return not_found(pvmw);
> + return true;
> }
> + /* THP pmd was split under us: handle on pte level */
> + spin_unlock(pvmw->ptl);
> + pvmw->ptl = NULL;
> } else if (!pmd_present(pmde)) {
> /*
> * If PVMW_SYNC, take and drop THP pmd lock so that we
> --
> 2.26.2
>

--
Peter Xu