Re: [PATCH v8 1/2] mm: introduce process_mrelease system call
From: Suren Baghdasaryan
Date: Mon Aug 09 2021 - 12:23:44 EST
On Mon, Aug 9, 2021 at 8:23 AM Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
> On Sun, Aug 8, 2021 at 9:08 AM Suren Baghdasaryan <surenb@xxxxxxxxxx> 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  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).
> >  https://lore.kernel.org/lkml/20190411014353.113252-3-surenb@xxxxxxxxxx/
> >  https://lore.kernel.org/linux-api/20201113173448.1863419-1-surenb@xxxxxxxxxx/
> >  https://lore.kernel.org/linux-api/20201124053943.1684874-3-surenb@xxxxxxxxxx/
> >  https://lore.kernel.org/linux-api/20201223075712.GA4719@xxxxxx/
> > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
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.