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 [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@xxxxxxxxxx/ > > [2] https://lore.kernel.org/linux-api/20201113173448.1863419-1-surenb@xxxxxxxxxx/ > > [3] https://lore.kernel.org/linux-api/20201124053943.1684874-3-surenb@xxxxxxxxxx/ > > [4] 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.
