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Subject[patch 7/7 -mm] oom: remove unnecessary code and cleanup
Remove the redundancy in __oom_kill_task() since:

- init can never be passed to this function: it will never be PF_EXITING
or selectable from select_bad_process(), and

- it will never be passed a task from oom_kill_task() without an ->mm
and we're unconcerned about detachment from exiting tasks, there's no
reason to protect them against SIGKILL or access to memory reserves.

Also moves the kernel log message to a higher level since the verbosity
is not always emitted here; we need not print an error message if an
exiting task is given a longer timeslice.

Signed-off-by: David Rientjes <rientjes@google.com>
---
mm/oom_kill.c | 64 ++++++++++++++------------------------------------------
1 files changed, 16 insertions(+), 48 deletions(-)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -400,67 +400,35 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
dump_tasks(mem);
}

-#define K(x) ((x) << (PAGE_SHIFT-10))
-
/*
- * 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
- * set.
+ * Give the oom killed task high priority and access to memory reserves so that
+ * it may quickly exit and free its memory.
*/
-static void __oom_kill_task(struct task_struct *p, int verbose)
+static void __oom_kill_task(struct task_struct *p)
{
- if (is_global_init(p)) {
- WARN_ON(1);
- printk(KERN_WARNING "tried to kill init!\n");
- return;
- }
-
- task_lock(p);
- if (!p->mm) {
- WARN_ON(1);
- printk(KERN_WARNING "tried to kill an mm-less task %d (%s)!\n",
- task_pid_nr(p), p->comm);
- task_unlock(p);
- return;
- }
-
- if (verbose)
- printk(KERN_ERR "Killed process %d (%s) "
- "vsz:%lukB, anon-rss:%lukB, file-rss:%lukB\n",
- task_pid_nr(p), p->comm,
- K(p->mm->total_vm),
- K(get_mm_counter(p->mm, MM_ANONPAGES)),
- K(get_mm_counter(p->mm, MM_FILEPAGES)));
- task_unlock(p);
-
- /*
- * We give our sacrificial lamb high priority and access to
- * all the memory it needs. That way it should be able to
- * exit() and clear out its resources quickly...
- */
p->rt.time_slice = HZ;
set_tsk_thread_flag(p, TIF_MEMDIE);
-
force_sig(SIGKILL, p);
}

+#define K(x) ((x) << (PAGE_SHIFT-10))
static int oom_kill_task(struct task_struct *p)
{
- /* WARNING: mm may not be dereferenced since we did not obtain its
- * value from get_task_mm(p). This is OK since all we need to do is
- * compare mm to q->mm below.
- *
- * Furthermore, even if mm contains a non-NULL value, p->mm may
- * change to NULL at any time since we do not hold task_lock(p).
- * However, this is of no concern to us.
- */
- if (!p->mm || p->signal->oom_adj == OOM_DISABLE)
+ task_lock(p);
+ if (!p->mm || p->signal->oom_adj == OOM_DISABLE) {
+ task_unlock(p);
return 1;
+ }
+ pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB\n",
+ task_pid_nr(p), p->comm, K(p->mm->total_vm),
+ K(get_mm_counter(p->mm, MM_ANONPAGES)),
+ K(get_mm_counter(p->mm, MM_FILEPAGES)));
+ task_unlock(p);

- __oom_kill_task(p, 1);
-
+ __oom_kill_task(p);
return 0;
}
+#undef K

static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
unsigned int points, unsigned long totalpages,
@@ -479,7 +447,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
* its children or threads, just set TIF_MEMDIE so it can die quickly
*/
if (p->flags & PF_EXITING) {
- __oom_kill_task(p, 0);
+ __oom_kill_task(p);
return 0;
}


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