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Subject: Re: [PATCH v6 1/2] mm: introduce process_mrelease system call
To:     Suren Baghdasaryan <surenb@google.com>, akpm@linux-foundation.org
Cc:     mhocko@kernel.org, mhocko@suse.com, rientjes@google.com,
        willy@infradead.org, hannes@cmpxchg.org, guro@fb.com,
        riel@surriel.com, minchan@kernel.org, christian@brauner.io,
        hch@infradead.org, oleg@redhat.com, jannh@google.com,
        shakeelb@google.com, luto@kernel.org, christian.brauner@ubuntu.com,
        fweimer@redhat.com, jengelh@inai.de, timmurray@google.com,
        linux-api@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, kernel-team@android.com
References: <20210804185004.1304692-1-surenb@google.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <9e218f0a-460f-cc49-f495-848ebaff8b6f@redhat.com>
Date:   Wed, 4 Aug 2021 20:58:25 +0200
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On 04.08.21 20:50, Suren Baghdasaryan 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 pidofd_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/
> 

Acked-by: David Hildenbrand <david@redhat.com>


-- 
Thanks,

David / dhildenb