Re: [patch 7/7 -mm] oom: remove unnecessary code and cleanup

KAMEZAWA Hiroyuki
2010-02-12T00:16:12Z

On Wed, 10 Feb 2010 08:32:24 -0800 (PST)
David Rientjes <rientjes@google.com> wrote:

> 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>

If you say "never", it's better to add BUG_ON() rather than
if (!p->mm)...

But yes, this patch seesm to remove unnecessary codes.
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.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;
> }
>
>