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Date: Mon, 15 Feb 2010 17:09:52 +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>,
Rik van Riel <riel@...hat.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Nick Piggin <npiggin@...e.de>,
Andrea Arcangeli <aarcange@...hat.com>,
Balbir Singh <balbir@...ux.vnet.ibm.com>,
Lubos Lunak <l.lunak@...e.cz>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [patch 5/7 -mm] oom: replace sysctls with quick mode
> Two VM sysctls, oom dump_tasks and oom_kill_allocating_task, were
> implemented for very large systems to avoid excessively long tasklist
> scans. The former suppresses helpful diagnostic messages that are
> emitted for each thread group leader that are candidates for oom kill
> including their pid, uid, vm size, rss, oom_adj value, and name; this
> information is very helpful to users in understanding why a particular
> task was chosen for kill over others. The latter simply kills current,
> the task triggering the oom condition, instead of iterating through the
> tasklist looking for the worst offender.
>
> Both of these sysctls are combined into one for use on the aforementioned
> large systems: oom_kill_quick. This disables the now-default
> oom_dump_tasks and kills current whenever the oom killer is called.
>
> The oom killer rewrite is the perfect opportunity to combine both sysctls
> into one instead of carrying around the others for years to come for
> nothing else than legacy purposes.
"_quick" is always bad sysctl name. instead, turnning oom_dump_tasks on
by default is better.
plus, this patch makes unnecessary compatibility issue.
>
> Signed-off-by: David Rientjes <rientjes@...gle.com>
> ---
> Documentation/sysctl/vm.txt | 44 +++++-------------------------------------
> include/linux/oom.h | 3 +-
> kernel/sysctl.c | 13 ++---------
> mm/oom_kill.c | 9 +++----
> 4 files changed, 14 insertions(+), 55 deletions(-)
>
> diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
> --- a/Documentation/sysctl/vm.txt
> +++ b/Documentation/sysctl/vm.txt
> @@ -43,9 +43,8 @@ Currently, these files are in /proc/sys/vm:
> - nr_pdflush_threads
> - nr_trim_pages (only if CONFIG_MMU=n)
> - numa_zonelist_order
> -- oom_dump_tasks
> - oom_forkbomb_thres
> -- oom_kill_allocating_task
> +- oom_kill_quick
> - overcommit_memory
> - overcommit_ratio
> - page-cluster
> @@ -470,27 +469,6 @@ this is causing problems for your system/application.
>
> ==============================================================
>
> -oom_dump_tasks
> -
> -Enables a system-wide task dump (excluding kernel threads) to be
> -produced when the kernel performs an OOM-killing and includes such
> -information as pid, uid, tgid, vm size, rss, cpu, oom_adj score, and
> -name. This is helpful to determine why the OOM killer was invoked
> -and to identify the rogue task that caused it.
> -
> -If this is set to zero, this information is suppressed. On very
> -large systems with thousands of tasks it may not be feasible to dump
> -the memory state information for each one. Such systems should not
> -be forced to incur a performance penalty in OOM conditions when the
> -information may not be desired.
> -
> -If this is set to non-zero, this information is shown whenever the
> -OOM killer actually kills a memory-hogging task.
> -
> -The default value is 0.
> -
> -==============================================================
> -
> oom_forkbomb_thres
>
> This value defines how many children with a seperate address space a specific
> @@ -511,22 +489,12 @@ The default value is 1000.
>
> ==============================================================
>
> -oom_kill_allocating_task
> -
> -This enables or disables killing the OOM-triggering task in
> -out-of-memory situations.
> -
> -If this is set to zero, the OOM killer will scan through the entire
> -tasklist and select a task based on heuristics to kill. This normally
> -selects a rogue memory-hogging task that frees up a large amount of
> -memory when killed.
> -
> -If this is set to non-zero, the OOM killer simply kills the task that
> -triggered the out-of-memory condition. This avoids the expensive
> -tasklist scan.
> +oom_kill_quick
>
> -If panic_on_oom is selected, it takes precedence over whatever value
> -is used in oom_kill_allocating_task.
> +When enabled, this will always kill the task that triggered the oom killer, i.e.
> +the task that attempted to allocate memory that could not be found. It also
> +suppresses the tasklist dump to the kernel log whenever the oom killer is
> +called. Typically set on systems with an extremely large number of tasks.
>
> The default value is 0.
>
> diff --git a/include/linux/oom.h b/include/linux/oom.h
> --- a/include/linux/oom.h
> +++ b/include/linux/oom.h
> @@ -51,8 +51,7 @@ static inline void oom_killer_enable(void)
> }
> /* for sysctl */
> extern int sysctl_panic_on_oom;
> -extern int sysctl_oom_kill_allocating_task;
> -extern int sysctl_oom_dump_tasks;
> +extern int sysctl_oom_kill_quick;
> extern int sysctl_oom_forkbomb_thres;
>
> #endif /* __KERNEL__*/
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -949,16 +949,9 @@ static struct ctl_table vm_table[] = {
> .proc_handler = proc_dointvec,
> },
> {
> - .procname = "oom_kill_allocating_task",
> - .data = &sysctl_oom_kill_allocating_task,
> - .maxlen = sizeof(sysctl_oom_kill_allocating_task),
> - .mode = 0644,
> - .proc_handler = proc_dointvec,
> - },
> - {
> - .procname = "oom_dump_tasks",
> - .data = &sysctl_oom_dump_tasks,
> - .maxlen = sizeof(sysctl_oom_dump_tasks),
> + .procname = "oom_kill_quick",
> + .data = &sysctl_oom_kill_quick,
> + .maxlen = sizeof(sysctl_oom_kill_quick),
> .mode = 0644,
> .proc_handler = proc_dointvec,
> },
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -32,9 +32,8 @@
> #include <linux/security.h>
>
> int sysctl_panic_on_oom;
> -int sysctl_oom_kill_allocating_task;
> -int sysctl_oom_dump_tasks;
> int sysctl_oom_forkbomb_thres = DEFAULT_OOM_FORKBOMB_THRES;
> +int sysctl_oom_kill_quick;
> static DEFINE_SPINLOCK(zone_scan_lock);
>
> /*
> @@ -397,7 +396,7 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
> dump_stack();
> mem_cgroup_print_oom_info(mem, p);
> show_mem();
> - if (sysctl_oom_dump_tasks)
> + if (!sysctl_oom_kill_quick)
> dump_tasks(mem);
> }
>
> @@ -604,9 +603,9 @@ static void __out_of_memory(gfp_t gfp_mask, int order, unsigned long totalpages,
> struct task_struct *p;
> unsigned int points;
>
> - if (sysctl_oom_kill_allocating_task)
> + if (sysctl_oom_kill_quick)
> if (!oom_kill_process(current, gfp_mask, order, 0, totalpages,
> - NULL, "Out of memory (oom_kill_allocating_task)"))
> + NULL, "Out of memory (quick mode)"))
> return;
> retry:
> /*
>
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