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 sIC3068g e6/5v9hFlonGWT4LVgm8xLNGckeTWQYX7+UfU4KRoEgHknZUY0EqbZFwA+oGXm7bFvZbgds6ukISE4UoO1uj9xxCPjPv5zUFeoC+8btzH/COtlQcCHlbTsJT880/mioSytk09rl0v3Wocr36LO926edt8LuiNkKyQwHlxIvF6ACZ2LmJJ2Ss/LdhrK1z5dx3Kn6mU/hM8o7y9Hf/IHzAMn0i4lj2s9hN6hDZekHc4pBeC37h7kJRE2wT0LxMxsu/fg/cfQnI05DJFEsZ9wvMNfcptiqB9Lcl5QHpb0pzWM1rX3mIcLHOPRSeTqaRlmdvwzHczKd9Ld1NQZfEM7c4aQYVD/n88YPSE8QyIyAT83q/8mhhBYrobKxXafl3EaeeTcFkiEhwI4nEVIR5EdzZc6g1MUwgweKQ00HKuLJdYxpwOsLI8Njf4R1MgZ+vveU4YrpnaC1hgLngXRe5MLv0zwFeAyUuFVSPHjqwv X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 1/14/25 7:06 AM, David Hildenbrand wrote: > On 14.01.25 15:52, Lorenzo Stoakes wrote: >> On Tue, Jan 14, 2025 at 02:01:32PM +0100, David Hildenbrand wrote: >>> On 13.01.25 23:30, Yang Shi wrote: >>>> When creating private mapping for /dev/zero, the driver makes it an >>>> anonymous mapping by calling set_vma_anonymous().  But it just sets >>>> vm_ops to NULL, vm_file is still valid and vm_pgoff is also file >>>> offset. >>>> >>>> This is a special case and the VMA doesn't look like either >>>> anonymous VMA >>>> or file VMA.  It confused other kernel subsystem, for example, >>>> khugepaged [1]. >>>> >>>> It seems pointless to keep such special case.  Making private >>>> /dev/zero> >>> mapping a full anonymous mapping doesn't change the semantic of >>>> /dev/zero either. >>>> >>>> The user visible effect is the mapping entry shown in >>>> /proc//smaps >>>> and /proc//maps. >>>> >>>> Before the change: >>>> ffffb7190000-ffffb7590000 rw-p 00001000 00:06 >>>> 8                          /dev/zero >>>> >>>> After the change: >>>> ffffb6130000-ffffb6530000 rw-p 00000000 00:00 0 >>>> >>> >>> Hm, not sure about this. It's actually quite consistent to have that >>> output >>> in smaps the way it is. You mapped a file at an offset, and it >>> behaves like >>> an anonymous mapping apart from that. >>> >>> Not sure if the buggy khugepaged thing is a good indicator to >>> warrant this >>> change. I admit this may be a concern, but I doubt who really care about it... >> >> Yeah, this is a user-facing fundamental change that hides information >> and >> defies expectation so I mean - it's a no go really isn't it? >> >> I'd rather we _not_ make this anon though, because isn't life confusing >> enough David? I thought it was bad enough with 'anon, file and lol >> shmem' >> but 'lol lol also /dev/zero' is enough to make me want to frolick in the >> fields... > > I recall there are users that rely on this memory to get the shared > zeropage on reads etc (in comparison to shmem!), so I better not ... > mess with this *at all* :) The behavior won't be changed.