[patch] oom: print triggering task's cpuset and mems allowed - Kernel

This is a discussion on [patch] oom: print triggering task's cpuset and mems allowed - Kernel ; When cpusets are enabled, it's necessary to print the triggering task's set of allowable nodes so the subsequently printed meminfo can be interpreted correctly. We also print the task's cpuset name for informational purposes. Cc: Paul Menage Signed-off-by: David Rientjes ...

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Thread: [patch] oom: print triggering task's cpuset and mems allowed

  1. [patch] oom: print triggering task's cpuset and mems allowed

    When cpusets are enabled, it's necessary to print the triggering task's
    set of allowable nodes so the subsequently printed meminfo can be
    interpreted correctly.

    We also print the task's cpuset name for informational purposes.

    Cc: Paul Menage
    Signed-off-by: David Rientjes
    ---
    include/linux/cpuset.h | 7 +++++++
    kernel/cpuset.c | 15 +++++++++++++++
    mm/oom_kill.c | 22 ++++++++++++++++++++++
    3 files changed, 44 insertions(+), 0 deletions(-)

    diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
    --- a/include/linux/cpuset.h
    +++ b/include/linux/cpuset.h
    @@ -79,6 +79,7 @@ extern void cpuset_track_online_nodes(void);
    extern int current_cpuset_is_being_rebound(void);

    extern void rebuild_sched_domains(void);
    +extern int cpuset_get_name(struct task_struct *p, size_t len, char *buffer);

    #else /* !CONFIG_CPUSETS */

    @@ -163,6 +164,12 @@ static inline void rebuild_sched_domains(void)
    partition_sched_domains(1, NULL, NULL);
    }

    +static inline int cpuset_get_name(struct task_struct *p, size_t len,
    + char *buffer)
    +{
    + return 0;
    +}
    +
    #endif /* !CONFIG_CPUSETS */

    #endif /* _LINUX_CPUSET_H */
    diff --git a/kernel/cpuset.c b/kernel/cpuset.c
    --- a/kernel/cpuset.c
    +++ b/kernel/cpuset.c
    @@ -2339,6 +2339,21 @@ int cpuset_mems_allowed_intersects(const struct task_struct *tsk1,
    return nodes_intersects(tsk1->mems_allowed, tsk2->mems_allowed);
    }

    +/**
    + * cpuset_get_name - grabs the name of @task's cpuset
    + * @task: pointer to task_struct of some task.
    + *
    + * Description: Place @task's cpuset name in @buffer and return the
    + * number of characters copied. Must hold task_lock(task).
    + */
    +int cpuset_get_name(struct task_struct *task, size_t len, char *buffer)
    +{
    + struct dentry *dentry;
    + dentry = task_cs(task)->css.cgroup->dentry;
    + return snprintf(buffer, len,
    + dentry ? (const char *)dentry->d_name.name : "/");
    +}
    +
    /*
    * Collection of memory_pressure is suppressed unless
    * this flag is enabled by writing "1" to the special
    diff --git a/mm/oom_kill.c b/mm/oom_kill.c
    --- a/mm/oom_kill.c
    +++ b/mm/oom_kill.c
    @@ -305,6 +305,27 @@ static void dump_tasks(const struct mem_cgroup *mem)
    } while_each_thread(g, p);
    }

    +#ifdef CONFIG_CPUSETS
    +#define BUFFER_LEN (256)
    +
    +static void print_task_cpuset(struct task_struct *p)
    +{
    + char buffer[BUFFER_LEN];
    +
    + if (cpuset_get_name(current, BUFFER_LEN, buffer) > 0) {
    + char nodelist[BUFFER_LEN];
    +
    + nodelist_scnprintf(nodelist, BUFFER_LEN, current->mems_allowed);
    + printk(KERN_ERR "%s cpuset=%s mems_allowed=%s\n",
    + current->comm, buffer, nodelist);
    + }
    +}
    +#else
    +static inline void print_task_cpuset(struct task_struct *p)
    +{
    +}
    +#endif
    +
    /*
    * Send SIGKILL to the selected process irrespective of CAP_SYS_RAW_IO
    * flag though it's unlikely that we select a process with CAP_SYS_RAW_IO
    @@ -391,6 +412,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
    printk(KERN_WARNING "%s invoked oom-killer: "
    "gfp_mask=0x%x, order=%d, oomkilladj=%d\n",
    current->comm, gfp_mask, order, current->oomkilladj);
    + print_task_cpuset(current);
    dump_stack();
    show_mem();
    if (sysctl_oom_dump_tasks)
    --
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  2. Re: [patch] oom: print triggering task's cpuset and mems allowed

    On Fri, 24 Oct 2008 17:15:32 -0700 (PDT)
    David Rientjes wrote:

    > +#ifdef CONFIG_CPUSETS
    > +#define BUFFER_LEN (256)
    > +
    > +static void print_task_cpuset(struct task_struct *p)
    > +{
    > + char buffer[BUFFER_LEN];
    > +
    > + if (cpuset_get_name(p, BUFFER_LEN, buffer) > 0) {
    > + char nodelist[BUFFER_LEN];
    > +
    > + nodelist_scnprintf(nodelist, BUFFER_LEN, p->mems_allowed);
    > + printk(KERN_ERR "%s cpuset=%s mems_allowed=%s\n",
    > + p->comm, buffer, nodelist);
    > + }
    > +}
    > +#else
    > +static inline void print_task_cpuset(struct task_struct *p)
    > +{
    > +}
    > +#endif
    > +
    > /*
    > * Send SIGKILL to the selected process irrespective of CAP_SYS_RAW_IO
    > * flag though it's unlikely that we select a process with CAP_SYS_RAW_IO
    > @@ -391,6 +412,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
    > printk(KERN_WARNING "%s invoked oom-killer: "
    > "gfp_mask=0x%x, order=%d, oomkilladj=%d\n",
    > current->comm, gfp_mask, order, current->oomkilladj);
    > + print_task_cpuset(current);
    > dump_stack();
    > show_mem();
    > if (sysctl_oom_dump_tasks)


    We can call the oom-killer at very very deep nesting levels, and adding
    another 512 bytes of stack consuption to that call path is really
    risky. Perhaps use statically allocated buffers protected by a local
    spinlock?

    Also, 256 bytes might be overkill for storing the cpuset's name?

    Also, it's Just Wrong that this code has to hardwire private knowledge
    of the max possible length of a cpuset name and of the
    nodelist_scnprintf() return string. These things should be controlled
    by a single #define in a shared header file.


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  3. Re: [patch] oom: print triggering task's cpuset and mems allowed

    On Tue, 28 Oct 2008 09:08:15 -0700 (PDT)
    David Rientjes wrote:

    > +#define CPUSET_NAME_LEN (128)
    > +#define CPUSET_NODELIST_LEN (256)
    > +static char cpuset_name[CPUSET_NAME_LEN];
    > +static char cpuset_nodelist[CPUSET_NODELIST_LEN];
    >
    > ...
    >
    > + snprintf(cpuset_name, CPUSET_NAME_LEN,
    > + dentry ? (const char *)dentry->d_name.name : "/");


    nit: this requires that the reviewer (and the maintainer) ensure that
    CPUSET_NAME_LEN=sizeof(cpuset_name). This must be done manually and
    introduces risk.

    Better would be:


    static char cpuset_name[128];

    ....

    snprintf(cpuset_name, sizeof(cpuset_name), ...);

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