Re: [PATCH v8 1/2] mm: introduce process_mrelease system call

[Suren Baghdasaryan <surenb@google.com>]

On Mon, Aug 9, 2021 at 9:23 AM Suren Baghdasaryan <surenb@google.com> wrote:
>
> On Mon, Aug 9, 2021 at 8:23 AM Shakeel Butt <shakeelb@google.com> wrote:
> >
> > On Sun, Aug 8, 2021 at 9:08 AM Suren Baghdasaryan <surenb@google.com> wrote:
> > >
> > > In modern systems it's not unusual to have a system component monitoring
> > > memory conditions of the system and tasked with keeping system memory
> > > pressure under control. One way to accomplish that is to kill
> > > non-essential processes to free up memory for more important ones.
> > > Examples of this are Facebook's OOM killer daemon called oomd and
> > > Android's low memory killer daemon called lmkd.
> > > For such system component it's important to be able to free memory
> > > quickly and efficiently. Unfortunately the time process takes to free
> > > up its memory after receiving a SIGKILL might vary based on the state
> > > of the process (uninterruptible sleep), size and OPP level of the core
> > > the process is running. A mechanism to free resources of the target
> > > process in a more predictable way would improve system's ability to
> > > control its memory pressure.
> > > Introduce process_mrelease system call that releases memory of a dying
> > > process from the context of the caller. This way the memory is freed in
> > > a more controllable way with CPU affinity and priority of the caller.
> > > The workload of freeing the memory will also be charged to the caller.
> > > The operation is allowed only on a dying process.
> > >
> > > After previous discussions [1, 2, 3] the decision was made [4] to introduce
> > > a dedicated system call to cover this use case.
> > >
> > > The API is as follows,
> > >
> > >           int process_mrelease(int pidfd, unsigned int flags);
> > >
> > >         DESCRIPTION
> > >           The process_mrelease() system call is used to free the memory of
> > >           an exiting process.
> > >
> > >           The pidfd selects the process referred to by the PID file
> > >           descriptor.
> > >           (See pidfd_open(2) for further information)
> > >
> > >           The flags argument is reserved for future use; currently, this
> > >           argument must be specified as 0.
> > >
> > >         RETURN VALUE
> > >           On success, process_mrelease() returns 0. On error, -1 is
> > >           returned and errno is set to indicate the error.
> > >
> > >         ERRORS
> > >           EBADF  pidfd is not a valid PID file descriptor.
> > >
> > >           EAGAIN Failed to release part of the address space.
> > >
> > >           EINTR  The call was interrupted by a signal; see signal(7).
> > >
> > >           EINVAL flags is not 0.
> > >
> > >           EINVAL The memory of the task cannot be released because the
> > >                  process is not exiting, the address space is shared
> > >                  with another live process or there is a core dump in
> > >                  progress.
> > >
> > >           ENOSYS This system call is not supported, for example, without
> > >                  MMU support built into Linux.
> > >
> > >           ESRCH  The target process does not exist (i.e., it has terminated
> > >                  and been waited on).
> > >
> > > [1] https://lore.kernel.org/lkml/20190411014353.113252-3-surenb@google.com/
> > > [2] https://lore.kernel.org/linux-api/20201113173448.1863419-1-surenb@google.com/
> > > [3] https://lore.kernel.org/linux-api/20201124053943.1684874-3-surenb@google.com/
> > > [4] https://lore.kernel.org/linux-api/20201223075712.GA4719@lst.de/
> > >
> > > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> >
> > Reviewed-by: Shakeel Butt <shakeelb@google.com>
>
> Thanks folks! I'll make the change Christian suggested and will push
> the next version carrying Acks along, including the one from David
> which I forgot to carry in this one.

v9 posted at: https://lore.kernel.org/linux-mm/20210809185259.405936-1-surenb@google.com