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    Subject[patch -mm v2] mm: introduce oom_adj_child
    It's helpful to be able to specify an oom_adj value for newly forked
    children that do not share memory with the parent.

    Before making oom_adj values a characteristic of a task's mm in
    2ff05b2b4eac2e63d345fc731ea151a060247f53, it was possible to change the
    oom_adj value of a vfork() child prior to execve() without implicitly
    changing the oom_adj value of the parent. With the new behavior, the
    oom_adj values of both threads would change since they represent the same
    memory.

    That change was necessary to fix an oom killer livelock which would occur
    when a child would be selected for oom kill prior to execve() and the
    task could not be killed because it shared memory with an OOM_DISABLE
    parent. In fact, only the most negative (most immune) oom_adj value for
    all threads sharing the same memory would actually be used by the oom
    killer, leaving inconsistencies amongst all other threads having
    different oom_adj values (and, thus, incorrectly exported
    /proc/pid/oom_score values).

    This patch adds a new per-process parameter: /proc/pid/oom_adj_child.
    This defaults to mirror the value of /proc/pid/oom_adj but may be changed
    so that mm's initialized by their children are preferred over the parent
    by the oom killer. Setting oom_adj_child to be less (i.e. more immune)
    than the task's oom_adj value itself is governed by the CAP_SYS_RESOURCE
    capability.

    When a mm is initialized, the initial oom_adj value will be set to the
    parent's oom_adj_child. This allows tasks to elevate the oom_adj value
    of a vfork'd child prior to execve() before the execution actually takes
    place.

    Furthermore, /proc/pid/oom_adj_child is inherited from the task that
    forked it.

    Cc: Rik van Riel <riel@redhat.com>
    Cc: Paul Menage <menage@google.com>
    Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Signed-off-by: David Rientjes <rientjes@google.com>
    ---
    Documentation/filesystems/proc.txt | 38 ++++++++++++++++----
    fs/proc/base.c | 68 ++++++++++++++++++++++++++++++++++++
    include/linux/sched.h | 1 +
    kernel/fork.c | 3 +-
    4 files changed, 101 insertions(+), 9 deletions(-)

    diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
    --- a/Documentation/filesystems/proc.txt
    +++ b/Documentation/filesystems/proc.txt
    @@ -34,10 +34,11 @@ Table of Contents

    3 Per-Process Parameters
    3.1 /proc/<pid>/oom_adj - Adjust the oom-killer score
    - 3.2 /proc/<pid>/oom_score - Display current oom-killer score
    - 3.3 /proc/<pid>/io - Display the IO accounting fields
    - 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
    - 3.5 /proc/<pid>/mountinfo - Information about mounts
    + 3.2 /proc/<pid>/oom_adj_child - Change default oom_adj for children
    + 3.3 /proc/<pid>/oom_score - Display current oom-killer score
    + 3.4 /proc/<pid>/io - Display the IO accounting fields
    + 3.5 /proc/<pid>/coredump_filter - Core dump filtering settings
    + 3.6 /proc/<pid>/mountinfo - Information about mounts


    ------------------------------------------------------------------------------
    @@ -1206,7 +1207,28 @@ The task with the highest badness score is then selected and its children
    are killed, process itself will be killed in an OOM situation when it does
    not have children or some of them disabled oom like described above.

    -3.2 /proc/<pid>/oom_score - Display current oom-killer score
    +
    +3.2 /proc/<pid>/oom_adj_child - Change default oom_adj for children
    +-------------------------------------------------------------------
    +
    +This file can be used to change the default oom_adj value for children when a
    +new mm is initialized. The oom_adj value for a child's mm is typically the
    +task's oom_adj value itself, however this value can be altered by writing to
    +this file.
    +
    +This is particularly helpful when a child is vfork'd and its mm following exec
    +should have a higher priority oom_adj value than its parent. The new mm will
    +default to oom_adj_child of the parent task.
    +
    +oom_adj_child will mirror oom_adj whenever the latter changes for all tasks
    +that share its memory. This avoids having to set both values when simply
    +tuning oom_adj and that value should be inherited by all children.
    +
    +Setting oom_adj_child to be more immune than the task's mm itself (i.e. less
    +than oom_adj) is governed by the CAP_SYS_RESOURCE capability.
    +
    +
    +3.3 /proc/<pid>/oom_score - Display current oom-killer score
    -------------------------------------------------------------

    This file can be used to check the current score used by the oom-killer is for
    @@ -1214,7 +1236,7 @@ any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which
    process should be killed in an out-of-memory situation.


    -3.3 /proc/<pid>/io - Display the IO accounting fields
    +3.4 /proc/<pid>/io - Display the IO accounting fields
    -------------------------------------------------------

    This file contains IO statistics for each running process
    @@ -1316,7 +1338,7 @@ those 64-bit counters, process A could see an intermediate result.
    More information about this can be found within the taskstats documentation in
    Documentation/accounting.

    -3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
    +3.5 /proc/<pid>/coredump_filter - Core dump filtering settings
    ---------------------------------------------------------------
    When a process is dumped, all anonymous memory is written to a core file as
    long as the size of the core file isn't limited. But sometimes we don't want
    @@ -1360,7 +1382,7 @@ For example:
    $ echo 0x7 > /proc/self/coredump_filter
    $ ./some_program

    -3.5 /proc/<pid>/mountinfo - Information about mounts
    +3.6 /proc/<pid>/mountinfo - Information about mounts
    --------------------------------------------------------

    This file contains lines of the form:
    diff --git a/fs/proc/base.c b/fs/proc/base.c
    --- a/fs/proc/base.c
    +++ b/fs/proc/base.c
    @@ -1023,6 +1023,7 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
    size_t count, loff_t *ppos)
    {
    struct task_struct *task;
    + struct task_struct *g, *p;
    char buffer[PROC_NUMBUF], *end;
    int oom_adjust;

    @@ -1051,6 +1052,12 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
    put_task_struct(task);
    return -EACCES;
    }
    + read_lock(&tasklist_lock);
    + do_each_thread(g, p) {
    + if (p->mm && p->mm == task->mm)
    + p->oom_adj_child = oom_adjust;
    + } while_each_thread(g, p);
    + read_unlock(&tasklist_lock);
    task->mm->oom_adj = oom_adjust;
    task_unlock(task);
    put_task_struct(task);
    @@ -1064,6 +1071,65 @@ static const struct file_operations proc_oom_adjust_operations = {
    .write = oom_adjust_write,
    };

    +static ssize_t oom_adj_child_read(struct file *file, char __user *buf,
    + size_t count, loff_t *ppos)
    +{
    + struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
    + char buffer[PROC_NUMBUF];
    + size_t len;
    + int oom_adj_child;
    +
    + if (!task)
    + return -ESRCH;
    + oom_adj_child = task->oom_adj_child;
    + put_task_struct(task);
    +
    + len = snprintf(buffer, sizeof(buffer), "%i\n", oom_adj_child);
    +
    + return simple_read_from_buffer(buf, count, ppos, buffer, len);
    +}
    +
    +static ssize_t oom_adj_child_write(struct file *file, const char __user *buf,
    + size_t count, loff_t *ppos)
    +{
    + struct task_struct *task;
    + char buffer[PROC_NUMBUF], *end;
    + int oom_adj_child;
    +
    + memset(buffer, 0, sizeof(buffer));
    + if (count > sizeof(buffer) - 1)
    + count = sizeof(buffer) - 1;
    + if (copy_from_user(buffer, buf, count))
    + return -EFAULT;
    + oom_adj_child = simple_strtol(buffer, &end, 0);
    + if ((oom_adj_child < OOM_ADJUST_MIN ||
    + oom_adj_child > OOM_ADJUST_MAX) && oom_adj_child != OOM_DISABLE)
    + return -EINVAL;
    + if (*end == '\n')
    + end++;
    + task = get_proc_task(file->f_path.dentry->d_inode);
    + if (!task)
    + return -ESRCH;
    + task_lock(task);
    + if (task->mm && oom_adj_child < task->mm->oom_adj &&
    + !capable(CAP_SYS_RESOURCE)) {
    + task_unlock(task);
    + put_task_struct(task);
    + return -EINVAL;
    + }
    + task_unlock(task);
    + task->oom_adj_child = oom_adj_child;
    + put_task_struct(task);
    + if (end - buffer == 0)
    + return -EIO;
    + return end - buffer;
    +}
    +
    +static const struct file_operations proc_oom_adj_child_operations = {
    + .read = oom_adj_child_read,
    + .write = oom_adj_child_write,
    +};
    +
    #ifdef CONFIG_AUDITSYSCALL
    #define TMPBUFLEN 21
    static ssize_t proc_loginuid_read(struct file * file, char __user * buf,
    @@ -2548,6 +2614,7 @@ static const struct pid_entry tgid_base_stuff[] = {
    #endif
    INF("oom_score", S_IRUGO, proc_oom_score),
    REG("oom_adj", S_IRUGO|S_IWUSR, proc_oom_adjust_operations),
    + REG("oom_adj_child", S_IRUGO|S_IWUSR, proc_oom_adj_child_operations),
    #ifdef CONFIG_AUDITSYSCALL
    REG("loginuid", S_IWUSR|S_IRUGO, proc_loginuid_operations),
    REG("sessionid", S_IRUGO, proc_sessionid_operations),
    @@ -2886,6 +2953,7 @@ static const struct pid_entry tid_base_stuff[] = {
    #endif
    INF("oom_score", S_IRUGO, proc_oom_score),
    REG("oom_adj", S_IRUGO|S_IWUSR, proc_oom_adjust_operations),
    + REG("oom_adj_child", S_IRUGO|S_IWUSR, proc_oom_adj_child_operations),
    #ifdef CONFIG_AUDITSYSCALL
    REG("loginuid", S_IWUSR|S_IRUGO, proc_loginuid_operations),
    REG("sessionid", S_IRUSR, proc_sessionid_operations),
    diff --git a/include/linux/sched.h b/include/linux/sched.h
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -1198,6 +1198,7 @@ struct task_struct {
    * a short time
    */
    unsigned char fpu_counter;
    + s8 oom_adj_child; /* Default child OOM-kill score adjustment */
    #ifdef CONFIG_BLK_DEV_IO_TRACE
    unsigned int btrace_seq;
    #endif
    diff --git a/kernel/fork.c b/kernel/fork.c
    --- a/kernel/fork.c
    +++ b/kernel/fork.c
    @@ -426,7 +426,7 @@ static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)
    init_rwsem(&mm->mmap_sem);
    INIT_LIST_HEAD(&mm->mmlist);
    mm->flags = (current->mm) ? current->mm->flags : default_dump_filter;
    - mm->oom_adj = (current->mm) ? current->mm->oom_adj : 0;
    + mm->oom_adj = p->oom_adj_child;
    mm->core_state = NULL;
    mm->nr_ptes = 0;
    set_mm_counter(mm, file_rss, 0);
    @@ -679,6 +679,7 @@ good_mm:

    tsk->mm = mm;
    tsk->active_mm = mm;
    + tsk->oom_adj_child = mm->oom_adj;
    return 0;

    fail_nomem:

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