Re: [PATCH] Increase default MLOCK_LIMIT to 8 MiB

On Wed, Nov 24, 2021 at 03:14:00PM +0100, David Hildenbrand wrote:

I'm not aware of any where you can fragment 50% of all pageblocks in the
system as an unprivileged user essentially consuming almost no memory
and essentially staying inside well-defined memlock limits. But sure if
there are "many" people will be able to come up with at least one
comparable thing. I'll be happy to learn.

If the concern is that THP's can be DOS'd then any avenue that renders
the system out of THPs is a DOS attack vector. Including all the
normal workloads that people run and already complain that THPs get
exhausted.

A hostile userspace can only quicken this process.

My position that FOLL_LONGTERM for unprivileged users is a strong no-go
stands as it is.

As this basically excludes long standing pre-existing things like
RDMA, XDP, io_uring, and more I don't think this can be the general
answer for mm, sorry.

Sure, lets stop now since I don't think we can agree.

Jason