LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: David Hildenbrand <david@redhat.com>
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
Subject: Re: [PATCH v4 1/2] mm: introduce process_mrelease system call
Date: Tue, 3 Aug 2021 09:48:06 +0200	[thread overview]
Message-ID: <95eff329-a7b1-dc2d-026c-fd61e476c846@redhat.com> (raw)
In-Reply-To: <20210802221431.2251210-1-surenb@google.com>

[...]

> Previously I proposed a number of alternatives to accomplish this:
> - https://lore.kernel.org/patchwork/patch/1060407 extending

I have no idea how stable these links are. Referencing via message id is 
the common practice. For this link, we'd use

https://lkml.kernel.org/r/20190411014353.113252-3-surenb@google.com/

instead.

> pidfd_send_signal to allow memory reaping using oom_reaper thread;
> - https://lore.kernel.org/patchwork/patch/1338196 extending
> pidfd_send_signal to reap memory of the target process synchronously from
> the context of the caller;
> - https://lore.kernel.org/patchwork/patch/1344419/ to add MADV_DONTNEED
> support for process_madvise implementing synchronous memory reaping.
> 
> The end of the last discussion culminated with suggestion to introduce a
> dedicated system call (https://lore.kernel.org/patchwork/patch/1344418/#1553875)
> The reasoning was that the new variant of process_madvise
>    a) does not work on an address range
>    b) is destructive
>    c) doesn't share much code at all with the rest of process_madvise
>  From the userspace point of view it was awkward and inconvenient to provide
> memory range for this operation that operates on the entire address space.
> Using special flags or address values to specify the entire address space
> was too hacky.

I'd condense this description and only reference previous discussions to 
put a main focus on what this patch actually does. Like

"
After previous discussions [1, 2, 3] the decision was made to introduce 
a dedicated system call to cover this use case.

...

[1] https://lkml.kernel.org/r/20190411014353.113252-3-surenb@google.com/
"

> 
> 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
>            a process which was sent a SIGKILL signal.
> 
>            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 task does not have a pending SIGKILL or its memory is
>                   shared with another process with no pending SIGKILL.

Hm, I do wonder if it would make sense to have a mode (e.g., via a flag) 
to reap all but shared memory from a dying process. Future work.

> 
>            ENOSYS This system call is not supported by kernels built with no
>                   MMU support (CONFIG_MMU=n).

Maybe "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).
> 
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
> changes in v4:
> - Replaced mmap_read_lock() with mmap_read_lock_killable(), per Michal Hocko
> - Added EINTR error in the manual pages documentation
> 
>   mm/oom_kill.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 58 insertions(+)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index c729a4c4a1ac..86727794b0a8 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -28,6 +28,7 @@
>   #include <linux/sched/task.h>
>   #include <linux/sched/debug.h>
>   #include <linux/swap.h>
> +#include <linux/syscalls.h>
>   #include <linux/timex.h>
>   #include <linux/jiffies.h>
>   #include <linux/cpuset.h>
> @@ -1141,3 +1142,60 @@ void pagefault_out_of_memory(void)
>   	out_of_memory(&oc);
>   	mutex_unlock(&oom_lock);
>   }
> +
> +SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags)
> +{
> +#ifdef CONFIG_MMU
> +	struct mm_struct *mm = NULL;
> +	struct task_struct *task;
> +	unsigned int f_flags;
> +	struct pid *pid;
> +	long ret = 0;
> +
> +	if (flags != 0)

if (flags)

> +		return -EINVAL;
> +
> +	pid = pidfd_get_pid(pidfd, &f_flags);
> +	if (IS_ERR(pid))
> +		return PTR_ERR(pid);
> +
> +	task = get_pid_task(pid, PIDTYPE_PID);
> +	if (!task) {
> +		ret = -ESRCH;
> +		goto put_pid;
> +	}
> +
> +	/*
> +	 * If the task is dying and in the process of releasing its memory
> +	 * then get its mm.
> +	 */
> +	task_lock(task);
> +	if (task_will_free_mem(task) && (task->flags & PF_KTHREAD) == 0) {
> +		mm = task->mm;
> +		mmget(mm);
> +	}
> +	task_unlock(task);
> +	if (!mm) {
> +		ret = -EINVAL;
> +		goto put_task;
> +	}
> +
> +	if (mmap_read_lock_killable(mm)) {
> +		ret = -EINTR;
> +		goto put_mm;
> +	}
> +	if (!__oom_reap_task_mm(mm))
> +		ret = -EAGAIN;

I'm not an expert on __oom_reap_task_mm(), but the whole approach makes 
sense to. So feel free to add my

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

-- 
Thanks,

David / dhildenb


  parent reply	other threads:[~2021-08-03  7:48 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-02 22:14 Suren Baghdasaryan
2021-08-02 22:14 ` [PATCH v4 2/2] mm: wire up syscall process_mrelease Suren Baghdasaryan
2021-08-03  7:48 ` David Hildenbrand [this message]
2021-08-03 17:19   ` [PATCH v4 1/2] mm: introduce process_mrelease system call Suren Baghdasaryan
2021-08-03  8:39 ` Michal Hocko
2021-08-03 17:27   ` Suren Baghdasaryan
2021-08-03 22:09     ` Suren Baghdasaryan
2021-08-04  6:21       ` Michal Hocko
2021-08-04 16:54         ` Suren Baghdasaryan

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=95eff329-a7b1-dc2d-026c-fd61e476c846@redhat.com \
    --to=david@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=christian.brauner@ubuntu.com \
    --cc=christian@brauner.io \
    --cc=fweimer@redhat.com \
    --cc=guro@fb.com \
    --cc=hannes@cmpxchg.org \
    --cc=hch@infradead.org \
    --cc=jannh@google.com \
    --cc=jengelh@inai.de \
    --cc=kernel-team@android.com \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=luto@kernel.org \
    --cc=mhocko@kernel.org \
    --cc=mhocko@suse.com \
    --cc=minchan@kernel.org \
    --cc=oleg@redhat.com \
    --cc=riel@surriel.com \
    --cc=rientjes@google.com \
    --cc=shakeelb@google.com \
    --cc=surenb@google.com \
    --cc=timmurray@google.com \
    --cc=willy@infradead.org \
    --subject='Re: [PATCH v4 1/2] mm: introduce process_mrelease system call' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).