Re: [PATCH v10 3/3] mm: add anonymous vma name refcounting

[Rasmus Villemoes]

On 07/10/2021 21.02, John Hubbard wrote:
> On 10/7/21 11:50, Suren Baghdasaryan wrote:
> ...

>>>> The desire is for one of these two parties to be a human who can get
>>>> the data and use it as is without additional conversions.
>>>> /proc/$pid/maps could report FD numbers instead of pathnames, which
>>>> could be converted to pathnames in userspace. However we do not do
>>>> that because pathnames are more convenient for humans to identify a
>>>> specific resource. Same logic applies here IMHO.
>>>
>>> Yes, please. It really seems like the folks that are interested in this
>>> feature want strings. (I certainly do.) For those not interested in the
>>> feature, it sounds like a CONFIG to keep it away would be sufficient.
>>> Can we just move forward with that?
>>
>> Would love to if others are ok with this.
>>
> 
> If this doesn't get accepted, then another way forward would to continue
> the ideas above to their logical conclusion, and create a new file system:
> vma-fs. 

Or: Why can't the library/application that wants a VMA backed by memory
to have some associated name not just

  fd = open("/run/named-vmas/foobar#24", O_CLOEXEC|O_RDWR|O_EXCL|O_CREAT);
  unlink("/run/named-vmas/foobar#24");
  ftruncate(fd, ...);
  mmap(fd);

where /run/named-vmas is a tmpfs (probably with some per-user/per-app
subdirs). That requires no changes in the kernel at all. Yes, it lacks
the automatic cleanup of using real anon mmap in case there's a crash
between open and unlink, but in an environment like Android that should
be solvable.

Rasmus