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Date: Wed, 2 Sep 2009 12:56:57 +0900
From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: nishimura@....nes.nec.co.jp,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [mmotm][PATCH 1/2] memcg: softlimit clean up
On Wed, 2 Sep 2009 09:34:38 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> This patch clean up/fixes for memcg's uncharge soft limit path.
> This is also a preparation for batched uncharge. When batched uncharge is
> introduced, calls for res_counter_uncharge() will be reduced and event
> counter will not work correctly. This tries to fix it.
>
> Problems:
> Now, res_counter_charge()/uncharge() handles softlimit information at
> charge/uncharge. Its softlimit-check is done when event counter per memcg
> goes over limit. But event counter per memcg is updated only when
> when res_counter tells it's over soft limit. And ancerstors of memcg are
> handled in "charge" path but not in "uncharge" path.
>
> Prolems:
> 1. memcg's event counter incremented only when softlimit hits. That's bad.
> It makes event counter hard to be reused for other purpose.
> 2. At uncharge, only the lowest level rescounter is handled. This is bug.
> Because ancesotor's event counter is not incremented, children should
> take care of them.
> 3. res_counter_uncharge()'s 3rd argument is NULL in most case.
> ops under res_counter->lock should be small.
> No "if" in res_counter is better.
>
> Fixes:
> 1. make event-counter of memcg checked at every charge/uncharge.
> (per-cpu area is not slow, no problem.)
>
> 2.All ancestors are checked at soft-limit-check. This is necessary because
> ancesotor's event counter may never be modified. Then, they should be
> checked at the same time. This fixes uncharge path.
>
> 2. Removed soft_limit_xx poitner and from charge and uncharge calls.
> Do-check-only-when-event counter expires scheme works well without them.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
Nice cleanups and fixes.
IMHO, softlimit codes become easier to understand.
Reviewed-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Thanks,
Daisuke Nishimura.
> ---
> include/linux/res_counter.h | 6 --
> kernel/res_counter.c | 18 ------
> mm/memcontrol.c | 115 +++++++++++++++++++-------------------------
> 3 files changed, 55 insertions(+), 84 deletions(-)
>
> Index: mmotm-2.6.31-Aug27/kernel/res_counter.c
> ===================================================================
> --- mmotm-2.6.31-Aug27.orig/kernel/res_counter.c
> +++ mmotm-2.6.31-Aug27/kernel/res_counter.c
> @@ -37,27 +37,17 @@ int res_counter_charge_locked(struct res
> }
>
> int res_counter_charge(struct res_counter *counter, unsigned long val,
> - struct res_counter **limit_fail_at,
> - struct res_counter **soft_limit_fail_at)
> + struct res_counter **limit_fail_at)
> {
> int ret;
> unsigned long flags;
> struct res_counter *c, *u;
>
> *limit_fail_at = NULL;
> - if (soft_limit_fail_at)
> - *soft_limit_fail_at = NULL;
> local_irq_save(flags);
> for (c = counter; c != NULL; c = c->parent) {
> spin_lock(&c->lock);
> ret = res_counter_charge_locked(c, val);
> - /*
> - * With soft limits, we return the highest ancestor
> - * that exceeds its soft limit
> - */
> - if (soft_limit_fail_at &&
> - !res_counter_soft_limit_check_locked(c))
> - *soft_limit_fail_at = c;
> spin_unlock(&c->lock);
> if (ret < 0) {
> *limit_fail_at = c;
> @@ -85,8 +75,7 @@ void res_counter_uncharge_locked(struct
> counter->usage -= val;
> }
>
> -void res_counter_uncharge(struct res_counter *counter, unsigned long val,
> - bool *was_soft_limit_excess)
> +void res_counter_uncharge(struct res_counter *counter, unsigned long val)
> {
> unsigned long flags;
> struct res_counter *c;
> @@ -94,9 +83,6 @@ void res_counter_uncharge(struct res_cou
> local_irq_save(flags);
> for (c = counter; c != NULL; c = c->parent) {
> spin_lock(&c->lock);
> - if (was_soft_limit_excess)
> - *was_soft_limit_excess =
> - !res_counter_soft_limit_check_locked(c);
> res_counter_uncharge_locked(c, val);
> spin_unlock(&c->lock);
> }
> Index: mmotm-2.6.31-Aug27/include/linux/res_counter.h
> ===================================================================
> --- mmotm-2.6.31-Aug27.orig/include/linux/res_counter.h
> +++ mmotm-2.6.31-Aug27/include/linux/res_counter.h
> @@ -114,8 +114,7 @@ void res_counter_init(struct res_counter
> int __must_check res_counter_charge_locked(struct res_counter *counter,
> unsigned long val);
> int __must_check res_counter_charge(struct res_counter *counter,
> - unsigned long val, struct res_counter **limit_fail_at,
> - struct res_counter **soft_limit_at);
> + unsigned long val, struct res_counter **limit_fail_at);
>
> /*
> * uncharge - tell that some portion of the resource is released
> @@ -128,8 +127,7 @@ int __must_check res_counter_charge(stru
> */
>
> void res_counter_uncharge_locked(struct res_counter *counter, unsigned long val);
> -void res_counter_uncharge(struct res_counter *counter, unsigned long val,
> - bool *was_soft_limit_excess);
> +void res_counter_uncharge(struct res_counter *counter, unsigned long val);
>
> static inline bool res_counter_limit_check_locked(struct res_counter *cnt)
> {
> Index: mmotm-2.6.31-Aug27/mm/memcontrol.c
> ===================================================================
> --- mmotm-2.6.31-Aug27.orig/mm/memcontrol.c
> +++ mmotm-2.6.31-Aug27/mm/memcontrol.c
> @@ -353,16 +353,6 @@ __mem_cgroup_remove_exceeded(struct mem_
> }
>
> static void
> -mem_cgroup_insert_exceeded(struct mem_cgroup *mem,
> - struct mem_cgroup_per_zone *mz,
> - struct mem_cgroup_tree_per_zone *mctz)
> -{
> - spin_lock(&mctz->lock);
> - __mem_cgroup_insert_exceeded(mem, mz, mctz);
> - spin_unlock(&mctz->lock);
> -}
> -
> -static void
> mem_cgroup_remove_exceeded(struct mem_cgroup *mem,
> struct mem_cgroup_per_zone *mz,
> struct mem_cgroup_tree_per_zone *mctz)
> @@ -392,34 +382,40 @@ static bool mem_cgroup_soft_limit_check(
>
> static void mem_cgroup_update_tree(struct mem_cgroup *mem, struct page *page)
> {
> - unsigned long long prev_usage_in_excess, new_usage_in_excess;
> - bool updated_tree = false;
> + unsigned long long new_usage_in_excess;
> struct mem_cgroup_per_zone *mz;
> struct mem_cgroup_tree_per_zone *mctz;
> -
> - mz = mem_cgroup_zoneinfo(mem, page_to_nid(page), page_zonenum(page));
> + int nid = page_to_nid(page);
> + int zid = page_zonenum(page);
> mctz = soft_limit_tree_from_page(page);
>
> /*
> - * We do updates in lazy mode, mem's are removed
> - * lazily from the per-zone, per-node rb tree
> + * Necessary to update all ancestors when hierarchy is used.
> + * because their event counter is not touched.
> */
> - prev_usage_in_excess = mz->usage_in_excess;
> -
> - new_usage_in_excess = res_counter_soft_limit_excess(&mem->res);
> - if (prev_usage_in_excess) {
> - mem_cgroup_remove_exceeded(mem, mz, mctz);
> - updated_tree = true;
> - }
> - if (!new_usage_in_excess)
> - goto done;
> - mem_cgroup_insert_exceeded(mem, mz, mctz);
> -
> -done:
> - if (updated_tree) {
> - spin_lock(&mctz->lock);
> - mz->usage_in_excess = new_usage_in_excess;
> - spin_unlock(&mctz->lock);
> + for (; mem; mem = parent_mem_cgroup(mem)) {
> + mz = mem_cgroup_zoneinfo(mem, nid, zid);
> + new_usage_in_excess =
> + res_counter_soft_limit_excess(&mem->res);
> + /*
> + * We have to update the tree if mz is on RB-tree or
> + * mem is over its softlimit.
> + */
> + if (new_usage_in_excess || mz->on_tree) {
> + spin_lock(&mctz->lock);
> + /* if on-tree, remove it */
> + if (mz->on_tree)
> + __mem_cgroup_remove_exceeded(mem, mz, mctz);
> + /*
> + * if over soft limit, insert again. mz->usage_in_excess
> + * will be updated properly.
> + */
> + if (new_usage_in_excess)
> + __mem_cgroup_insert_exceeded(mem, mz, mctz);
> + else
> + mz->usage_in_excess = 0;
> + spin_unlock(&mctz->lock);
> + }
> }
> }
>
> @@ -1266,9 +1262,9 @@ static int __mem_cgroup_try_charge(struc
> gfp_t gfp_mask, struct mem_cgroup **memcg,
> bool oom, struct page *page)
> {
> - struct mem_cgroup *mem, *mem_over_limit, *mem_over_soft_limit;
> + struct mem_cgroup *mem, *mem_over_limit;
> int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> - struct res_counter *fail_res, *soft_fail_res = NULL;
> + struct res_counter *fail_res;
>
> if (unlikely(test_thread_flag(TIF_MEMDIE))) {
> /* Don't account this! */
> @@ -1300,17 +1296,16 @@ static int __mem_cgroup_try_charge(struc
>
> if (mem_cgroup_is_root(mem))
> goto done;
> - ret = res_counter_charge(&mem->res, PAGE_SIZE, &fail_res,
> - &soft_fail_res);
> + ret = res_counter_charge(&mem->res, PAGE_SIZE, &fail_res);
> if (likely(!ret)) {
> if (!do_swap_account)
> break;
> ret = res_counter_charge(&mem->memsw, PAGE_SIZE,
> - &fail_res, NULL);
> + &fail_res);
> if (likely(!ret))
> break;
> /* mem+swap counter fails */
> - res_counter_uncharge(&mem->res, PAGE_SIZE, NULL);
> + res_counter_uncharge(&mem->res, PAGE_SIZE);
> flags |= MEM_CGROUP_RECLAIM_NOSWAP;
> mem_over_limit = mem_cgroup_from_res_counter(fail_res,
> memsw);
> @@ -1349,16 +1344,11 @@ static int __mem_cgroup_try_charge(struc
> }
> }
> /*
> - * Insert just the ancestor, we should trickle down to the correct
> - * cgroup for reclaim, since the other nodes will be below their
> - * soft limit
> - */
> - if (soft_fail_res) {
> - mem_over_soft_limit =
> - mem_cgroup_from_res_counter(soft_fail_res, res);
> - if (mem_cgroup_soft_limit_check(mem_over_soft_limit))
> - mem_cgroup_update_tree(mem_over_soft_limit, page);
> - }
> + * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.
> + * if they exceeds softlimit.
> + */
> + if (mem_cgroup_soft_limit_check(mem))
> + mem_cgroup_update_tree(mem, page);
> done:
> return 0;
> nomem:
> @@ -1433,10 +1423,9 @@ static void __mem_cgroup_commit_charge(s
> if (unlikely(PageCgroupUsed(pc))) {
> unlock_page_cgroup(pc);
> if (!mem_cgroup_is_root(mem)) {
> - res_counter_uncharge(&mem->res, PAGE_SIZE, NULL);
> + res_counter_uncharge(&mem->res, PAGE_SIZE);
> if (do_swap_account)
> - res_counter_uncharge(&mem->memsw, PAGE_SIZE,
> - NULL);
> + res_counter_uncharge(&mem->memsw, PAGE_SIZE);
> }
> css_put(&mem->css);
> return;
> @@ -1515,7 +1504,7 @@ static int mem_cgroup_move_account(struc
> goto out;
>
> if (!mem_cgroup_is_root(from))
> - res_counter_uncharge(&from->res, PAGE_SIZE, NULL);
> + res_counter_uncharge(&from->res, PAGE_SIZE);
> mem_cgroup_charge_statistics(from, pc, false);
>
> page = pc->page;
> @@ -1535,7 +1524,7 @@ static int mem_cgroup_move_account(struc
> }
>
> if (do_swap_account && !mem_cgroup_is_root(from))
> - res_counter_uncharge(&from->memsw, PAGE_SIZE, NULL);
> + res_counter_uncharge(&from->memsw, PAGE_SIZE);
> css_put(&from->css);
>
> css_get(&to->css);
> @@ -1606,9 +1595,9 @@ uncharge:
> css_put(&parent->css);
> /* uncharge if move fails */
> if (!mem_cgroup_is_root(parent)) {
> - res_counter_uncharge(&parent->res, PAGE_SIZE, NULL);
> + res_counter_uncharge(&parent->res, PAGE_SIZE);
> if (do_swap_account)
> - res_counter_uncharge(&parent->memsw, PAGE_SIZE, NULL);
> + res_counter_uncharge(&parent->memsw, PAGE_SIZE);
> }
> return ret;
> }
> @@ -1799,8 +1788,7 @@ __mem_cgroup_commit_charge_swapin(struct
> * calling css_tryget
> */
> if (!mem_cgroup_is_root(memcg))
> - res_counter_uncharge(&memcg->memsw, PAGE_SIZE,
> - NULL);
> + res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
> mem_cgroup_swap_statistics(memcg, false);
> mem_cgroup_put(memcg);
> }
> @@ -1827,9 +1815,9 @@ void mem_cgroup_cancel_charge_swapin(str
> if (!mem)
> return;
> if (!mem_cgroup_is_root(mem)) {
> - res_counter_uncharge(&mem->res, PAGE_SIZE, NULL);
> + res_counter_uncharge(&mem->res, PAGE_SIZE);
> if (do_swap_account)
> - res_counter_uncharge(&mem->memsw, PAGE_SIZE, NULL);
> + res_counter_uncharge(&mem->memsw, PAGE_SIZE);
> }
> css_put(&mem->css);
> }
> @@ -1844,7 +1832,6 @@ __mem_cgroup_uncharge_common(struct page
> struct page_cgroup *pc;
> struct mem_cgroup *mem = NULL;
> struct mem_cgroup_per_zone *mz;
> - bool soft_limit_excess = false;
>
> if (mem_cgroup_disabled())
> return NULL;
> @@ -1884,10 +1871,10 @@ __mem_cgroup_uncharge_common(struct page
> }
>
> if (!mem_cgroup_is_root(mem)) {
> - res_counter_uncharge(&mem->res, PAGE_SIZE, &soft_limit_excess);
> + res_counter_uncharge(&mem->res, PAGE_SIZE);
> if (do_swap_account &&
> (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT))
> - res_counter_uncharge(&mem->memsw, PAGE_SIZE, NULL);
> + res_counter_uncharge(&mem->memsw, PAGE_SIZE);
> }
> if (ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
> mem_cgroup_swap_statistics(mem, true);
> @@ -1904,7 +1891,7 @@ __mem_cgroup_uncharge_common(struct page
> mz = page_cgroup_zoneinfo(pc);
> unlock_page_cgroup(pc);
>
> - if (soft_limit_excess && mem_cgroup_soft_limit_check(mem))
> + if (mem_cgroup_soft_limit_check(mem))
> mem_cgroup_update_tree(mem, page);
> /* at swapout, this memcg will be accessed to record to swap */
> if (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
> @@ -1982,7 +1969,7 @@ void mem_cgroup_uncharge_swap(swp_entry_
> * This memcg can be obsolete one. We avoid calling css_tryget
> */
> if (!mem_cgroup_is_root(memcg))
> - res_counter_uncharge(&memcg->memsw, PAGE_SIZE, NULL);
> + res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
> mem_cgroup_swap_statistics(memcg, false);
> mem_cgroup_put(memcg);
> }
>
--
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