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Date: Mon, 11 May 2009 09:17:58 +0900 (JST)
From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To: David Rientjes <rientjes@...gle.com>
Cc: kosaki.motohiro@...fujitsu.com,
Andrew Morton <akpm@...ux-foundation.org>,
Greg Kroah-Hartman <gregkh@...e.de>,
Nick Piggin <npiggin@...e.de>, Mel Gorman <mel@....ul.ie>,
Peter Ziljstra <a.p.ziljstra@...llo.nl>,
Christoph Lameter <cl@...ux-foundation.org>,
Dave Hansen <dave@...ux.vnet.ibm.com>,
San Mehat <san@...roid.com>, Arve Hjonnevag <arve@...roid.com>,
linux-kernel@...r.kernel.org
Subject: Re: [patch 06/11 -mmotm] oom: move oom_adj value from task_struct to mm_struct
> The per-task oom_adj value is a characteristic of its mm more than the
> task itself since it's not possible to oom kill any thread that shares
> the mm. If a task were to be killed while attached to an mm that could
> not be freed because another thread were set to OOM_DISABLE, it would
> have needlessly been terminated since there is no potential for future
> memory freeing.
>
> This patch moves oomkilladj (now more appropriately named oom_adj) from
> struct task_struct to struct mm_struct. This requires task_lock() on a
> task to check its oom_adj value to protect against exec, but it's already
> necessary to take the lock when dereferencing the mm to find the total VM
> size for the badness heuristic.
>
> This fixes a livelock if the oom killer chooses a task and another thread
> sharing the same memory has an oom_adj value of OOM_DISABLE. This occurs
> because oom_kill_task() repeatedly returns 1 and refuses to kill the
> chosen task while select_bad_process() will repeatedly choose the same
> task during the next retry.
>
> Taking task_lock() in select_bad_process() to check for OOM_DISABLE and
> in oom_kill_task() to check for threads sharing the same memory will be
> removed in the next patch in this series where it will no longer be
> necessary.
>
> Writing to /proc/pid/oom_adj for a kthread will now return -EINVAL since
> these threads are immune from oom killing already. They simply report an
> oom_adj value of OOM_DISABLE.
David, staging driver shold be standalone.
Please don't change core kernel for staging.
if you merge it into mainline, I suggest to you help the driver graduate
staging.
Thanks.
>
> Cc: Nick Piggin <npiggin@...e.de>
> Cc: San Mehat <san@...roid.com>
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
> Documentation/filesystems/proc.txt | 15 +++++++++----
> drivers/staging/android/lowmemorykiller.c | 2 +-
> fs/proc/base.c | 19 ++++++++++++++--
> include/linux/mm_types.h | 2 +
> include/linux/sched.h | 1 -
> mm/oom_kill.c | 32 ++++++++++++++++++----------
> 6 files changed, 49 insertions(+), 22 deletions(-)
>
> diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
> --- a/Documentation/filesystems/proc.txt
> +++ b/Documentation/filesystems/proc.txt
> @@ -1003,11 +1003,13 @@ CHAPTER 3: PER-PROCESS PARAMETERS
> 3.1 /proc/<pid>/oom_adj - Adjust the oom-killer score
> ------------------------------------------------------
>
> -This file can be used to adjust the score used to select which processes
> -should be killed in an out-of-memory situation. Giving it a high score will
> -increase the likelihood of this process being killed by the oom-killer. Valid
> -values are in the range -16 to +15, plus the special value -17, which disables
> -oom-killing altogether for this process.
> +This file can be used to adjust the score used to select which processes should
> +be killed in an out-of-memory situation. The oom_adj value is a characteristic
> +of the task's mm, so all threads that share an mm with pid will have the same
> +oom_adj value. A high value will increase the liklihood of this process being
> +killed by the oom-killer. Valid values are in the range -16 to +15 as
> +explained below and a special value of -17, which disables oom-killing
> +altogether for threads sharing pid's mm.
>
> The process to be killed in an out-of-memory situation is selected among all others
> based on its badness score. This value equals the original memory size of the process
> @@ -1021,6 +1023,9 @@ the parent's score if they do not share the same memory. Thus forking servers
> are the prime candidates to be killed. Having only one 'hungry' child will make
> parent less preferable than the child.
>
> +/proc/<pid>/oom_adj cannot be changed for kthreads since they are immune from
> +oom-killing already.
> +
> /proc/<pid>/oom_score shows process' current badness score.
>
> The following heuristics are then applied:
> diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
> --- a/drivers/staging/android/lowmemorykiller.c
> +++ b/drivers/staging/android/lowmemorykiller.c
> @@ -97,7 +97,7 @@ static int lowmem_shrink(int nr_to_scan, gfp_t gfp_mask)
> task_unlock(p);
> continue;
> }
> - oom_adj = p->oomkilladj;
> + oom_adj = p->mm->oom_adj;
> if (oom_adj < min_adj) {
> task_unlock(p);
> continue;
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1003,7 +1003,12 @@ static ssize_t oom_adjust_read(struct file *file, char __user *buf,
>
> if (!task)
> return -ESRCH;
> - oom_adjust = task->oomkilladj;
> + task_lock(task);
> + if (task->mm)
> + oom_adjust = task->mm->oom_adj;
> + else
> + oom_adjust = OOM_DISABLE;
> + task_unlock(task);
> put_task_struct(task);
>
> len = snprintf(buffer, sizeof(buffer), "%i\n", oom_adjust);
> @@ -1032,11 +1037,19 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
> task = get_proc_task(file->f_path.dentry->d_inode);
> if (!task)
> return -ESRCH;
> - if (oom_adjust < task->oomkilladj && !capable(CAP_SYS_RESOURCE)) {
> + task_lock(task);
> + if (!task->mm) {
> + task_unlock(task);
> + put_task_struct(task);
> + return -EINVAL;
> + }
> + if (oom_adjust < task->mm->oom_adj && !capable(CAP_SYS_RESOURCE)) {
> + task_unlock(task);
> put_task_struct(task);
> return -EACCES;
> }
> - task->oomkilladj = oom_adjust;
> + task->mm->oom_adj = oom_adjust;
> + task_unlock(task);
> put_task_struct(task);
> if (end - buffer == 0)
> return -EIO;
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -232,6 +232,8 @@ struct mm_struct {
>
> unsigned long saved_auxv[AT_VECTOR_SIZE]; /* for /proc/PID/auxv */
>
> + s8 oom_adj; /* OOM kill score adjustment (bit shift) */
> +
> cpumask_t cpu_vm_mask;
>
> /* Architecture-specific MM context */
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1149,7 +1149,6 @@ struct task_struct {
> * a short time
> */
> unsigned char fpu_counter;
> - s8 oomkilladj; /* OOM kill score adjustment (bit shift). */
> #ifdef CONFIG_BLK_DEV_IO_TRACE
> unsigned int btrace_seq;
> #endif
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -58,6 +58,7 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
> unsigned long points, cpu_time, run_time;
> struct mm_struct *mm;
> struct task_struct *child;
> + int oom_adj;
>
> task_lock(p);
> mm = p->mm;
> @@ -65,6 +66,7 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
> task_unlock(p);
> return 0;
> }
> + oom_adj = mm->oom_adj;
>
> /*
> * The memory size of the process is the basis for the badness.
> @@ -148,15 +150,15 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
> points /= 8;
>
> /*
> - * Adjust the score by oomkilladj.
> + * Adjust the score by oom_adj.
> */
> - if (p->oomkilladj) {
> - if (p->oomkilladj > 0) {
> + if (oom_adj) {
> + if (oom_adj > 0) {
> if (!points)
> points = 1;
> - points <<= p->oomkilladj;
> + points <<= oom_adj;
> } else
> - points >>= -(p->oomkilladj);
> + points >>= -(oom_adj);
> }
>
> #ifdef DEBUG
> @@ -251,8 +253,10 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
> *ppoints = ULONG_MAX;
> }
>
> - if (p->oomkilladj == OOM_DISABLE)
> + task_lock(p);
> + if (p->mm && p->mm->oom_adj == OOM_DISABLE)
> continue;
> + task_unlock(p);
>
> points = badness(p, uptime.tv_sec);
> if (points > *ppoints || !chosen) {
> @@ -304,8 +308,7 @@ static void dump_tasks(const struct mem_cgroup *mem)
> }
> printk(KERN_INFO "[%5d] %5d %5d %8lu %8lu %3d %3d %s\n",
> p->pid, __task_cred(p)->uid, p->tgid, mm->total_vm,
> - get_mm_rss(mm), (int)task_cpu(p), p->oomkilladj,
> - p->comm);
> + get_mm_rss(mm), (int)task_cpu(p), mm->oom_adj, p->comm);
> task_unlock(p);
> } while_each_thread(g, p);
> }
> @@ -367,8 +370,12 @@ static int oom_kill_task(struct task_struct *p)
> * Don't kill the process if any threads are set to OOM_DISABLE
> */
> do_each_thread(g, q) {
> - if (q->mm == mm && q->oomkilladj == OOM_DISABLE)
> + task_lock(q);
> + if (q->mm == mm && q->mm && q->mm->oom_adj == OOM_DISABLE) {
> + task_unlock(q);
> return 1;
> + }
> + task_unlock(q);
> } while_each_thread(g, q);
>
> __oom_kill_task(p, 1);
> @@ -393,10 +400,11 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
> struct task_struct *c;
>
> if (printk_ratelimit()) {
> - printk(KERN_WARNING "%s invoked oom-killer: "
> - "gfp_mask=0x%x, order=%d, oomkilladj=%d\n",
> - current->comm, gfp_mask, order, current->oomkilladj);
> task_lock(current);
> + printk(KERN_WARNING "%s invoked oom-killer: "
> + "gfp_mask=0x%x, order=%d, oom_adj=%d\n",
> + current->comm, gfp_mask, order,
> + current->mm ? current->mm->oom_adj : OOM_DISABLE);
> cpuset_print_task_mems_allowed(current);
> task_unlock(current);
> dump_stack();
> --
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