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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-1.fc44) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sun, 2026-10-11 at 03:52 +0800, Yuan-Hao Hsu wrote: > On Wed, 07 Oct 2026 06:47:06 -0400, Rik van Riel wrote: > > Since this is lockless, the PTEs could change under > > us between when we walk them in folio_pte_batch_flags() > > and the batched try_grab_folio(). > >=20 > > Is that race condition safe, or do we need to re-check > > afterward that: > > 1) the ptes still point at the same folio, and/or > > 2) the folio still spans the entire range, and was > > =C2=A0=C2=A0 not split before we grabbed the refcount? >=20 > It is safe, because the batch only runs after the first page of the > run has gone through the unchanged per-page path: the folio reference > is already held (and for FOLL_PIN the _pincount already raised, with > the smp_mb__after_atomic() in try_grab_folio_fast()) before any of > the other ptes is read. >=20 > 2) With that reference held the folio cannot be split: You are right. The page tables can still be remapped to point at something else after gup_fast_pte_range() grabs a reference to the folio, but that can happen no matter what precautions we take inside gup_fast, because it can happen after gup_fast has returned. I have no other concerns, so feel free to add my: Reviewed-by: Rik van Riel Could I convince you to take a look through my earlier series to make regular GUP go faster? If there are any issues left in that, I would like to fix them before the maintainers get around to reviewing that series: https://lore.kernel.org/r/20260811025157.1632867-1-riel@surriel.com/ --=20 All Rights Reversed.