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identity=mailfrom; envelope-from=""; helo=NAM11-CO1-obe.outbound.protection.outlook.com; client-ip=52.100.173.231 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616676128-423790 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000052, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Mar 25, 2021 at 01:09:14PM +0100, Christian K=C3=B6nig wrote: > Am 25.03.21 um 13:01 schrieb Jason Gunthorpe: > > On Thu, Mar 25, 2021 at 12:53:15PM +0100, Thomas Hellstr=C3=B6m (Inte= l) wrote: > >=20 > > > Nope. The point here was that in this case, to make sure mmap uses = the > > > correct VA to give us a reasonable chance of alignement, the driver= might > > > need to be aware of and do trickery with the huge page-table-entry = sizes > > > anyway, although I think in most cases a standard helper for this c= an be > > > supplied. > > Of course the driver needs some way to influence the VA mmap uses, > > gernally it should align to the natural page size of the device >=20 > Well a mmap() needs to be aligned to the page size of the CPU, but not > necessarily to the one of the device. >=20 > So I'm pretty sure the device driver should not be involved in any way = the > choosing of the VA for the CPU mapping. No, if the device wants to use huge pages it must influence the mmap VA or it can't form huge pgaes. It is the same reason why mmap returns 2M stuff these days to make THP possible Jason