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 iT7bJ8id 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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 9:46 AM, David Hildenbrand wrote: > On 14.01.25 18:38, Yang Shi wrote: >> >> >> >> 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. > > Note that MAP_PRIVATE of /dev/zero will also make it appear in the > same way right now (I just tried). Yes, I will add this in the commit log as another user visible change. > > The example is about MAP_FILE in general, not just MAP_SHARED IIUC. MAP_FILE is actually ignored on Linux per https://man7.org/linux/man-pages/man2/mmap.2.html. It also says "(regions created with the MAP_ANON | MAP_SHARED flags)". Anyway it looks like this man page may be a little bit outdated. We can clean it up later.