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 06Y0xwyI 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 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 9:23 AM, David Hildenbrand wrote: > On 14.01.25 18:01, Yang Shi wrote: >> >> >> >> 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... >> > > There is an example in the man page [1] about /proc/self/map_files/. > > I assume that will also change here. IIUC, that example is specific to "anonymous shared memory" created by shared mapping of /dev/zero. > > It's always hard to tell who that could affect, but I'm not convinced > this is worth it to find it out :) > >>>> >>>> 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. > > Yes, I know. And that's good ;) > > > [1] https://man7.org/linux/man-pages/man5/proc_pid_map_files.5.html >