Re: [PATCH v16 07/11] secretmem: use PMD-size pages to amortize direct map fragmentation

Mike Rapoport
2021-02-04T09:59:30Z

On Wed, Feb 03, 2021 at 10:12:22AM +0100, Michal Hocko wrote:
> On Tue 02-02-21 21:10:40, Mike Rapoport wrote:
> >
> > Let me reiterate to make sure I don't misread your suggestion.
> >
> > If we make secretmem an opt-in feature with, e.g. kernel parameter, the
> > pooling of large pages is unnecessary. In this case there is no limited
> > resource we need to protect because secretmem will allocate page by page.
>
> Yes.
>
> > Since there is no limited resource, we don't need special permissions
> > to access secretmem so we can move forward with a system call that creates
> > a mmapable file descriptor and save the hassle of a chardev.
>
> Yes, I assume you implicitly assume mlock rlimit here.

Yes.

> Also memcg accounting should be in place.

Right, without pools memcg accounting is no different from other
unevictable files.

> Wrt to the specific syscall, please document why existing interfaces are
> not a good fit as well. It would be also great to describe interaction
> with mlock itself (I assume the two to be incompatible - mlock will fail
> on and mlockall will ignore it).

The interaction with mlock() belongs more to the man page, but I don't mind
adding this to changelog as well.

--
Sincerely yours,
Mike.