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Date: Thu, 3 Jun 2010 15:06:19 +0900
From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Subject: Re: [PATCH 1/2] memcg clean up try_charge main loop
On Thu, 3 Jun 2010 11:48:37 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
> mem_cgroup_try_charge() has a big loop in it and seems to be hard to read.
> Most of routines are for slow path. This patch moves codes out from the
> loop and make it clear what's done.
>
> Summary:
> - refactoring a function to detect a memcg is under acccount move or not.
> - refactoring a function to wait for the end of moving task acct.
> - refactoring a main loop('s slow path) as a function and make it clear
> why we retry or quit by return code.
> - add fatal_signal_pending() check for bypassing charge loops.
>
> Changelog 2010-06-01
> - added fatal_signal_pending() to bypass charge loop. This is useful
> and valid to do because if signal is fatal, charging against it
> isn't very necessary and the user can see smooth kill even under
> heavy workload on a memcg.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
> mm/memcontrol.c | 247 +++++++++++++++++++++++++++++++++-----------------------
> 1 file changed, 148 insertions(+), 99 deletions(-)
>
> Index: mmotm-2.6.34-May21/mm/memcontrol.c
> ===================================================================
> --- mmotm-2.6.34-May21.orig/mm/memcontrol.c
> +++ mmotm-2.6.34-May21/mm/memcontrol.c
> @@ -1072,6 +1072,49 @@ static unsigned int get_swappiness(struc
> return swappiness;
> }
>
> +/* A routine for testing mem is not under move_account */
> +
> +static bool mem_cgroup_under_move(struct mem_cgroup *mem)
> +{
> + struct mem_cgroup *from = mc.from;
> + struct mem_cgroup *to = mc.to;
> + bool ret = false;
> +
> + if (from == mem || to == mem)
> + return true;
> +
> + if (!from || !to || !mem->use_hierarchy)
> + return false;
> +
> + rcu_read_lock();
> + if (css_tryget(&from->css)) {
> + ret = css_is_ancestor(&from->css, &mem->css);
> + css_put(&from->css);
> + }
> + if (!ret && css_tryget(&to->css)) {
> + ret = css_is_ancestor(&to->css, &mem->css);
> + css_put(&to->css);
> + }
> + rcu_read_unlock();
> + return ret;
> +}
> +
> +static bool mem_cgroup_wait_acct_move(struct mem_cgroup *mem)
> +{
> + if (mc.moving_task && current != mc.moving_task) {
> + if (mem_cgroup_under_move(mem)) {
> + DEFINE_WAIT(wait);
> + prepare_to_wait(&mc.waitq, &wait, TASK_INTERRUPTIBLE);
> + /* moving charge context might have finished. */
> + if (mc.moving_task)
> + schedule();
> + finish_wait(&mc.waitq, &wait);
> + return true;
> + }
> + }
> + return false;
> +}
> +
> static int mem_cgroup_count_children_cb(struct mem_cgroup *mem, void *data)
> {
> int *val = data;
> @@ -1582,16 +1625,83 @@ static int __cpuinit memcg_stock_cpu_cal
> return NOTIFY_OK;
> }
>
> +
> +/* See __mem_cgroup_try_charge() for details */
> +enum {
> + CHARGE_OK, /* success */
> + CHARGE_RETRY, /* need to retry but retry is not bad */
> + CHARGE_NOMEM, /* we can't do more. return -ENOMEM */
> + CHARGE_WOULDBLOCK, /* GFP_WAIT wasn't set and no enough res. */
> + CHARGE_OOM_DIE, /* the current is killed because of OOM */
> +};
> +
> +static int __mem_cgroup_do_charge(struct mem_cgroup *mem, gfp_t gfp_mask,
> + int csize, bool oom_check)
> +{
> + struct mem_cgroup *mem_over_limit;
> + struct res_counter *fail_res;
> + unsigned long flags = 0;
> + int ret;
> +
> + ret = res_counter_charge(&mem->res, csize, &fail_res);
> +
> + if (likely(!ret)) {
> + if (!do_swap_account)
> + return CHARGE_OK;
> + ret = res_counter_charge(&mem->memsw, csize, &fail_res);
> + if (likely(!ret))
> + return CHARGE_OK;
> +
> + mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
> + flags |= MEM_CGROUP_RECLAIM_NOSWAP;
> + } else
> + mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
> +
> + if (csize > PAGE_SIZE) /* change csize and retry */
> + return CHARGE_RETRY;
> +
> + if (!(gfp_mask & __GFP_WAIT))
> + return CHARGE_WOULDBLOCK;
> +
> + ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, NULL,
> + gfp_mask, flags);
> + /*
> + * try_to_free_mem_cgroup_pages() might not give us a full
> + * picture of reclaim. Some pages are reclaimed and might be
> + * moved to swap cache or just unmapped from the cgroup.
> + * Check the limit again to see if the reclaim reduced the
> + * current usage of the cgroup before giving up
> + */
> + if (ret || mem_cgroup_check_under_limit(mem_over_limit))
> + return CHARGE_RETRY;
> +
> + /*
> + * At task move, charge accounts can be doubly counted. So, it's
> + * better to wait until the end of task_move if something is going on.
> + */
> + if (mem_cgroup_wait_acct_move(mem_over_limit))
> + return CHARGE_RETRY;
> +
> + /* If we don't need to call oom-killer at el, return immediately */
> + if (!oom_check)
> + return CHARGE_NOMEM;
> + /* check OOM */
> + if (!mem_cgroup_handle_oom(mem_over_limit, gfp_mask))
> + return CHARGE_OOM_DIE;
> +
> + return CHARGE_RETRY;
> +}
> +
> /*
> * Unlike exported interface, "oom" parameter is added. if oom==true,
> * oom-killer can be invoked.
> */
> +
> static int __mem_cgroup_try_charge(struct mm_struct *mm,
> - gfp_t gfp_mask, struct mem_cgroup **memcg, bool oom)
> + gfp_t gfp_mask, struct mem_cgroup **memcg, bool oom)
> {
> - struct mem_cgroup *mem, *mem_over_limit;
> - int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> - struct res_counter *fail_res;
> + struct mem_cgroup *mem = NULL;
> + int ret = CHARGE_RETRY;
> int csize = CHARGE_SIZE;
>
it would be a nitpick, but how about:
int ret;
...
do {
...
} while (ret != CHARGE_OK);
?
> /*
> @@ -1609,120 +1719,57 @@ static int __mem_cgroup_try_charge(struc
> * thread group leader migrates. It's possible that mm is not
> * set, if so charge the init_mm (happens for pagecache usage).
> */
> - mem = *memcg;
> - if (likely(!mem)) {
> + if (*memcg) {
> + mem = *memcg;
> + css_get(&mem->css);
> + } else {
> mem = try_get_mem_cgroup_from_mm(mm);
> + if (unlikely(!mem))
> + return 0;
> *memcg = mem;
> - } else {
> - css_get(&mem->css);
> }
> - if (unlikely(!mem))
> - return 0;
>
> VM_BUG_ON(css_is_removed(&mem->css));
> if (mem_cgroup_is_root(mem))
> goto done;
>
> - while (1) {
> - int ret = 0;
> - unsigned long flags = 0;
> + while (ret != CHARGE_OK) {
> + int nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
> + bool oom_check;
>
> if (consume_stock(mem))
> - goto done;
> -
> - ret = res_counter_charge(&mem->res, csize, &fail_res);
> - if (likely(!ret)) {
> - if (!do_swap_account)
> - break;
> - ret = res_counter_charge(&mem->memsw, csize, &fail_res);
> - if (likely(!ret))
> - break;
> - /* mem+swap counter fails */
> - res_counter_uncharge(&mem->res, csize);
> - flags |= MEM_CGROUP_RECLAIM_NOSWAP;
> - mem_over_limit = mem_cgroup_from_res_counter(fail_res,
> - memsw);
> - } else
> - /* mem counter fails */
> - mem_over_limit = mem_cgroup_from_res_counter(fail_res,
> - res);
> + goto done; /* don't need to fill stock */
> + /* If killed, bypass charge */
> + if (fatal_signal_pending(current))
> + goto bypass;
>
> - /* reduce request size and retry */
> - if (csize > PAGE_SIZE) {
> - csize = PAGE_SIZE;
> - continue;
> + oom_check = false;
> + if (oom && !nr_oom_retries) {
> + oom_check = true;
> + nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
> }
Well, as I said before, nr_oom_retries seems to be reset at the begining of
this loop every time. Actually, I cannot cause oom even when I set a value
to limit_in_bytes and run a program which uses more memory than the limit,
because we never meet !nr_oom_retries here and oom_check will never be set to true.
Thanks,
Daisuke Nishimura.
> - if (!(gfp_mask & __GFP_WAIT))
> - goto nomem;
>
> - ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, NULL,
> - gfp_mask, flags);
> - if (ret)
> - continue;
> + ret = __mem_cgroup_do_charge(mem, gfp_mask, csize, oom_check);
>
> - /*
> - * try_to_free_mem_cgroup_pages() might not give us a full
> - * picture of reclaim. Some pages are reclaimed and might be
> - * moved to swap cache or just unmapped from the cgroup.
> - * Check the limit again to see if the reclaim reduced the
> - * current usage of the cgroup before giving up
> - *
> - */
> - if (mem_cgroup_check_under_limit(mem_over_limit))
> - continue;
> -
> - /* try to avoid oom while someone is moving charge */
> - if (mc.moving_task && current != mc.moving_task) {
> - struct mem_cgroup *from, *to;
> - bool do_continue = false;
> - /*
> - * There is a small race that "from" or "to" can be
> - * freed by rmdir, so we use css_tryget().
> - */
> - from = mc.from;
> - to = mc.to;
> - if (from && css_tryget(&from->css)) {
> - if (mem_over_limit->use_hierarchy)
> - do_continue = css_is_ancestor(
> - &from->css,
> - &mem_over_limit->css);
> - else
> - do_continue = (from == mem_over_limit);
> - css_put(&from->css);
> - }
> - if (!do_continue && to && css_tryget(&to->css)) {
> - if (mem_over_limit->use_hierarchy)
> - do_continue = css_is_ancestor(
> - &to->css,
> - &mem_over_limit->css);
> - else
> - do_continue = (to == mem_over_limit);
> - css_put(&to->css);
> - }
> - if (do_continue) {
> - DEFINE_WAIT(wait);
> - prepare_to_wait(&mc.waitq, &wait,
> - TASK_INTERRUPTIBLE);
> - /* moving charge context might have finished. */
> - if (mc.moving_task)
> - schedule();
> - finish_wait(&mc.waitq, &wait);
> - continue;
> - }
> - }
> -
> - if (!nr_retries--) {
> + switch (ret) {
> + case CHARGE_OK:
> + break;
> + case CHARGE_RETRY: /* not in OOM situation but retry */
> + csize = PAGE_SIZE;
> + break;
> + case CHARGE_WOULDBLOCK: /* !__GFP_WAIT */
> + goto nomem;
> + case CHARGE_NOMEM: /* OOM routine works */
> if (!oom)
> goto nomem;
> - if (mem_cgroup_handle_oom(mem_over_limit, gfp_mask)) {
> - nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> - continue;
> - }
> - /* When we reach here, current task is dying .*/
> - css_put(&mem->css);
> + /* If oom, we never return -ENOMEM */
> + nr_oom_retries--;
> + break;
> + case CHARGE_OOM_DIE: /* Killed by OOM Killer */
> goto bypass;
> }
> }
> +
> if (csize > PAGE_SIZE)
> refill_stock(mem, csize - PAGE_SIZE);
> done:
> @@ -1731,6 +1778,8 @@ nomem:
> css_put(&mem->css);
> return -ENOMEM;
> bypass:
> + if (mem)
> + css_put(&mem->css);
> *memcg = NULL;
> return 0;
> }
>
--
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