| Message ID | 20211001190938.14050-2-longman@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm, memcg: Miscellaneous cleanups | expand |
Hi Waiman,
I love your patch! Yet something to improve:
[auto build test ERROR on hnaz-mm/master]
url: https://github.com/0day-ci/linux/commits/Waiman-Long/mm-memcg-Miscellaneous-cleanups/20211002-031125
base: https://github.com/hnaz/linux-mm master
config: nios2-randconfig-r024-20211001 (attached as .config)
compiler: nios2-linux-gcc (GCC) 11.2.0
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# https://github.com/0day-ci/linux/commit/321484dcb4f16ca7bd626adf390222913d188ecc
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Waiman-Long/mm-memcg-Miscellaneous-cleanups/20211002-031125
git checkout 321484dcb4f16ca7bd626adf390222913d188ecc
# save the attached .config to linux build tree
mkdir build_dir
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=nios2 SHELL=/bin/bash
If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>
All errors (new ones prefixed by >>):
In file included from include/asm-generic/percpu.h:5,
from ./arch/nios2/include/generated/asm/percpu.h:1,
from include/linux/irqflags.h:17,
from include/asm-generic/cmpxchg.h:15,
from ./arch/nios2/include/generated/asm/cmpxchg.h:1,
from include/asm-generic/atomic.h:12,
from ./arch/nios2/include/generated/asm/atomic.h:1,
from include/linux/atomic.h:7,
from include/linux/page_counter.h:5,
from mm/memcontrol.c:28:
mm/memcontrol.c: In function 'refill_stock':
>> mm/memcontrol.c:2225:27: error: 'struct mem_cgroup' has no member named 'kmem_state'
2225 | if (unlikely(memcg->kmem_state != KMEM_ONLINE)) {
| ^~
include/linux/compiler.h:78:45: note: in definition of macro 'unlikely'
78 | # define unlikely(x) __builtin_expect(!!(x), 0)
| ^
vim +2225 mm/memcontrol.c
2212
2213 /*
2214 * Cache charges(val) to local per_cpu area.
2215 * This will be consumed by consume_stock() function, later.
2216 */
2217 static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
2218 {
2219 struct memcg_stock_pcp *stock;
2220 unsigned long flags;
2221
2222 /*
2223 * An offlined memcg shouldn't be put into stock.
2224 */
> 2225 if (unlikely(memcg->kmem_state != KMEM_ONLINE)) {
2226 cancel_charge(memcg, nr_pages);
2227 return;
2228 }
2229
2230 local_irq_save(flags);
2231
2232 stock = this_cpu_ptr(&memcg_stock);
2233 if (stock->cached != memcg) { /* reset if necessary */
2234 drain_stock(stock);
2235 css_get(&memcg->css);
2236 stock->cached = memcg;
2237 }
2238 stock->nr_pages += nr_pages;
2239
2240 if (stock->nr_pages > MEMCG_CHARGE_BATCH)
2241 drain_stock(stock);
2242
2243 local_irq_restore(flags);
2244 }
2245
---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
Hi Waiman,
I love your patch! Yet something to improve:
[auto build test ERROR on hnaz-mm/master]
url: https://github.com/0day-ci/linux/commits/Waiman-Long/mm-memcg-Miscellaneous-cleanups/20211002-031125
base: https://github.com/hnaz/linux-mm master
config: x86_64-randconfig-a016-20211001 (attached as .config)
compiler: clang version 14.0.0 (https://github.com/llvm/llvm-project 962e503cc8bc411f7523cc393acae8aae425b1c4)
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# https://github.com/0day-ci/linux/commit/321484dcb4f16ca7bd626adf390222913d188ecc
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Waiman-Long/mm-memcg-Miscellaneous-cleanups/20211002-031125
git checkout 321484dcb4f16ca7bd626adf390222913d188ecc
# save the attached .config to linux build tree
mkdir build_dir
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash
If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>
All errors (new ones prefixed by >>):
>> mm/memcontrol.c:2225:22: error: no member named 'kmem_state' in 'struct mem_cgroup'
if (unlikely(memcg->kmem_state != KMEM_ONLINE)) {
~~~~~ ^
include/linux/compiler.h:78:42: note: expanded from macro 'unlikely'
# define unlikely(x) __builtin_expect(!!(x), 0)
^
1 error generated.
vim +2225 mm/memcontrol.c
2212
2213 /*
2214 * Cache charges(val) to local per_cpu area.
2215 * This will be consumed by consume_stock() function, later.
2216 */
2217 static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
2218 {
2219 struct memcg_stock_pcp *stock;
2220 unsigned long flags;
2221
2222 /*
2223 * An offlined memcg shouldn't be put into stock.
2224 */
> 2225 if (unlikely(memcg->kmem_state != KMEM_ONLINE)) {
2226 cancel_charge(memcg, nr_pages);
2227 return;
2228 }
2229
2230 local_irq_save(flags);
2231
2232 stock = this_cpu_ptr(&memcg_stock);
2233 if (stock->cached != memcg) { /* reset if necessary */
2234 drain_stock(stock);
2235 css_get(&memcg->css);
2236 stock->cached = memcg;
2237 }
2238 stock->nr_pages += nr_pages;
2239
2240 if (stock->nr_pages > MEMCG_CHARGE_BATCH)
2241 drain_stock(stock);
2242
2243 local_irq_restore(flags);
2244 }
2245
---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
On Fri, Oct 01, 2021 at 03:09:36PM -0400, Waiman Long wrote: > When freeing a page associated with an offlined memcg, refill_stock() > will put it into local stock delaying its demise until another memcg > comes in to take its place in the stock. To avoid that, we now check > for offlined memcg and go directly in this case to the slowpath for > the uncharge via the repurposed cancel_charge() function. Hi Waiman! I'm afraid it can make a cleanup of a dying cgroup slower: for every released page we'll potentially traverse the whole cgroup tree and decrease atomic page counters. I'm not sure I understand the benefits we get from this change which do justify the slowdown on the cleanup path. Thanks! > > Signed-off-by: Waiman Long <longman@redhat.com> > --- > mm/memcontrol.c | 16 +++++++++++----- > 1 file changed, 11 insertions(+), 5 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 4b32896d87a2..4568363062c1 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2167,6 +2167,8 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages) > return ret; > } > > +static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages); > + > /* > * Returns stocks cached in percpu and reset cached information. > */ > @@ -2178,9 +2180,7 @@ static void drain_stock(struct memcg_stock_pcp *stock) > return; > > if (stock->nr_pages) { > - page_counter_uncharge(&old->memory, stock->nr_pages); > - if (do_memsw_account()) > - page_counter_uncharge(&old->memsw, stock->nr_pages); > + cancel_charge(old, stock->nr_pages); > stock->nr_pages = 0; > } > > @@ -2219,6 +2219,14 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) > struct memcg_stock_pcp *stock; > unsigned long flags; > > + /* > + * An offlined memcg shouldn't be put into stock. > + */ > + if (unlikely(memcg->kmem_state != KMEM_ONLINE)) { > + cancel_charge(memcg, nr_pages); > + return; > + } > + > local_irq_save(flags); > > stock = this_cpu_ptr(&memcg_stock); > @@ -2732,7 +2740,6 @@ static inline int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, > return try_charge_memcg(memcg, gfp_mask, nr_pages); > } > > -#if defined(CONFIG_MEMCG_KMEM) || defined(CONFIG_MMU) > static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages) > { > if (mem_cgroup_is_root(memcg)) > @@ -2742,7 +2749,6 @@ static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages) > if (do_memsw_account()) > page_counter_uncharge(&memcg->memsw, nr_pages); > } > -#endif > > static void commit_charge(struct folio *folio, struct mem_cgroup *memcg) > { > -- > 2.18.1 >
On 10/1/21 7:51 PM, Roman Gushchin wrote: > On Fri, Oct 01, 2021 at 03:09:36PM -0400, Waiman Long wrote: >> When freeing a page associated with an offlined memcg, refill_stock() >> will put it into local stock delaying its demise until another memcg >> comes in to take its place in the stock. To avoid that, we now check >> for offlined memcg and go directly in this case to the slowpath for >> the uncharge via the repurposed cancel_charge() function. > Hi Waiman! > > I'm afraid it can make a cleanup of a dying cgroup slower: for every > released page we'll potentially traverse the whole cgroup tree and > decrease atomic page counters. > > I'm not sure I understand the benefits we get from this change which > do justify the slowdown on the cleanup path. I am debugging a problem where some dying memcgs somehow stay around for a long time leading to gradual increase in memory consumption over time. I see the per-cpu stock as one of the places where a reference to a dying memcg may be present. Anyway, I agree that it may not help much. I am going to drop it if you think it is not a good idea. Cheers, Longman
On 10/1/21 19:51, Roman Gushchin wrote: > On Fri, Oct 01, 2021 at 03:09:36PM -0400, Waiman Long wrote: >> When freeing a page associated with an offlined memcg, refill_stock() >> will put it into local stock delaying its demise until another memcg >> comes in to take its place in the stock. To avoid that, we now check >> for offlined memcg and go directly in this case to the slowpath for >> the uncharge via the repurposed cancel_charge() function. > Hi Waiman! > > I'm afraid it can make a cleanup of a dying cgroup slower: for every > released page we'll potentially traverse the whole cgroup tree and > decrease atomic page counters. > > I'm not sure I understand the benefits we get from this change which > do justify the slowdown on the cleanup path. > > Thanks! I was notified of a lockdep splat that this patch may help to prevent. [18073.102101] ====================================================== [18073.102101] WARNING: possible circular locking dependency detected [18073.102101] 5.14.0-42.el9.x86_64+debug #1 Not tainted [18073.102101] ------------------------------------------------------ [18073.102101] bz1567074_bin/420270 is trying to acquire lock: [18073.102101] ffffffff9bdfc478 (css_set_lock){..-.}-{2:2}, at: obj_cgroup_release+0x79/0x210 [18073.102101] [18073.102101] but task is already holding lock: [18073.102101] ffff88806ba4ef18 (&sighand->siglock){-...}-{2:2}, at: force_sig_info_to_task+0x6c/0x370 [18073.102101] [18073.102101] which lock already depends on the new lock. [18073.102101] [18073.102101] [18073.102101] the existing dependency chain (in reverse order) is: [18073.102101] [18073.102101] -> #1 (&sighand->siglock){-...}-{2:2}: [18073.102101] __lock_acquire+0xb72/0x1870 [18073.102101] lock_acquire.part.0+0x117/0x340 [18073.102101] _raw_spin_lock_irqsave+0x43/0x90 [18073.102101] __lock_task_sighand+0xa0/0x210 [18073.102101] cgroup_freeze_task+0x6f/0x150 [18073.102101] cgroup_migrate_execute+0x25f/0xf90 [18073.102101] cgroup_update_dfl_csses+0x417/0x4f0 [18073.102101] cgroup_subtree_control_write+0x67b/0xa10 [18073.102101] cgroup_file_write+0x1ef/0x6a0 [18073.102101] kernfs_fop_write_iter+0x2c7/0x460 [18073.102101] new_sync_write+0x36f/0x610 [18073.102101] vfs_write+0x5c6/0x890 [18073.102101] ksys_write+0xf9/0x1d0 [18073.102101] do_syscall_64+0x3b/0x90 [18073.102101] entry_SYSCALL_64_after_hwframe+0x44/0xae [18073.102101] [18073.102101] -> #0 (css_set_lock){..-.}-{2:2}: [18073.102101] check_prev_add+0x15e/0x20f0 [18073.102101] validate_chain+0xac6/0xde0 [18073.102101] __lock_acquire+0xb72/0x1870 [18073.102101] lock_acquire.part.0+0x117/0x340 [18073.102101] _raw_spin_lock_irqsave+0x43/0x90 [18073.102101] obj_cgroup_release+0x79/0x210 [18073.102101] percpu_ref_put_many.constprop.0+0x16b/0x1a0 [18073.102101] drain_obj_stock+0x1a8/0x310 [18073.102101] refill_obj_stock+0xa4/0x480 [18073.102101] obj_cgroup_charge+0x104/0x240 [18073.102101] kmem_cache_alloc+0x94/0x400 [18073.102101] __sigqueue_alloc+0x1b9/0x460 [18073.102101] __send_signal+0x4b2/0xf60 [18073.102101] force_sig_info_to_task+0x226/0x370 [18073.102101] force_sig_fault+0xb0/0xf0 [18073.102101] noist_exc_debug+0xec/0x110 [18073.102101] asm_exc_debug+0x2b/0x30 [18073.102101] [18073.102101] other info that might help us debug this: [18073.102101] [18073.102101] Possible unsafe locking scenario: [18073.102101] [18073.102101] CPU0 CPU1 [18073.102101] ---- ---- [18073.102101] lock(&sighand->siglock); [18073.102101] lock(css_set_lock); [18073.102101] lock(&sighand->siglock); [18073.102101] lock(css_set_lock); [18073.102101] [18073.102101] *** DEADLOCK *** [18073.102101] [18073.102101] 2 locks held by bz1567074_bin/420270: [18073.102101] #0: ffff88806ba4ef18 (&sighand->siglock){-...}-{2:2}, at: force_sig_info_to_task+0x6c/0x370 [18073.102101] #1: ffffffff9bd0ea00 (rcu_read_lock){....}-{1:2}, at: percpu_ref_put_many.constprop.0+0x0/0x1a0 [18073.102101] [18073.102101] stack backtrace: [18073.102101] CPU: 0 PID: 420270 Comm: bz1567074_bin Kdump: loaded Not tainted 5.14.0-42.el9.x86_64+debug #1 [18073.102101] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2007 [18073.102101] Call Trace: [18073.102101] dump_stack_lvl+0x57/0x7d [18073.102101] check_noncircular+0x26a/0x310 [18073.102101] ? pvclock_clocksource_read+0x2b8/0x520 [18073.102101] ? print_circular_bug+0x1f0/0x1f0 [18073.102101] ? alloc_chain_hlocks+0x1de/0x530 [18073.102101] check_prev_add+0x15e/0x20f0 [18073.102101] validate_chain+0xac6/0xde0 [18073.102101] ? check_prev_add+0x20f0/0x20f0 [18073.102101] __lock_acquire+0xb72/0x1870 [18073.102101] ? __lock_acquire+0xb72/0x1870 [18073.102101] lock_acquire.part.0+0x117/0x340 [18073.102101] ? obj_cgroup_release+0x79/0x210 [18073.102101] ? rcu_read_unlock+0x40/0x40 [18073.102101] ? rcu_read_lock_sched_held+0x3f/0x70 [18073.102101] ? lock_acquire+0x224/0x2d0 [18073.102101] ? obj_cgroup_release+0x79/0x210 [18073.102101] _raw_spin_lock_irqsave+0x43/0x90 [18073.102101] ? obj_cgroup_release+0x79/0x210 [18073.102101] obj_cgroup_release+0x79/0x210 [18073.102101] percpu_ref_put_many.constprop.0+0x16b/0x1a0 [18073.102101] drain_obj_stock+0x1a8/0x310 [18073.102101] refill_obj_stock+0xa4/0x480 [18073.102101] obj_cgroup_charge+0x104/0x240 [18073.102101] ? __sigqueue_alloc+0x1b9/0x460 [18073.102101] kmem_cache_alloc+0x94/0x400 [18073.102101] ? __sigqueue_alloc+0x129/0x460 [18073.102101] __sigqueue_alloc+0x1b9/0x460 [18073.102101] __send_signal+0x4b2/0xf60 [18073.102101] ? send_signal+0x9f/0x580 [18073.102101] force_sig_info_to_task+0x226/0x370 [18073.102101] force_sig_fault+0xb0/0xf0 [18073.102101] ? force_sig_fault_to_task+0xe0/0xe0 [18073.102101] ? asm_exc_debug+0x23/0x30 [18073.102101] ? notify_die+0x88/0x100 [18073.102101] ? asm_exc_debug+0x23/0x30 [18073.102101] noist_exc_debug+0xec/0x110 [18073.102101] asm_exc_debug+0x2b/0x30 The &sighand->siglock => css_set_lock locking sequence is caused by a task holding sighand->siglock and call kmem_cache_alloc(GFP_ATOMIC) and the release of the obj_cgroup originally from an offlined memcg in percpu stock leading to the call of obj_cgroup_release() which takes the cs_set_lock. The chance of hitting that is very small, but it can still happen. So do you think addressing this possible deadlock scenario is worth the possible slower release of an offlined memcg? Cheers, Longman >> Signed-off-by: Waiman Long <longman@redhat.com> >> --- >> mm/memcontrol.c | 16 +++++++++++----- >> 1 file changed, 11 insertions(+), 5 deletions(-) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index 4b32896d87a2..4568363062c1 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -2167,6 +2167,8 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages) >> return ret; >> } >> >> +static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages); >> + >> /* >> * Returns stocks cached in percpu and reset cached information. >> */ >> @@ -2178,9 +2180,7 @@ static void drain_stock(struct memcg_stock_pcp *stock) >> return; >> >> if (stock->nr_pages) { >> - page_counter_uncharge(&old->memory, stock->nr_pages); >> - if (do_memsw_account()) >> - page_counter_uncharge(&old->memsw, stock->nr_pages); >> + cancel_charge(old, stock->nr_pages); >> stock->nr_pages = 0; >> } >> >> @@ -2219,6 +2219,14 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) >> struct memcg_stock_pcp *stock; >> unsigned long flags; >> >> + /* >> + * An offlined memcg shouldn't be put into stock. >> + */ >> + if (unlikely(memcg->kmem_state != KMEM_ONLINE)) { >> + cancel_charge(memcg, nr_pages); >> + return; >> + } >> + >> local_irq_save(flags); >> >> stock = this_cpu_ptr(&memcg_stock); >> @@ -2732,7 +2740,6 @@ static inline int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, >> return try_charge_memcg(memcg, gfp_mask, nr_pages); >> } >> >> -#if defined(CONFIG_MEMCG_KMEM) || defined(CONFIG_MMU) >> static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages) >> { >> if (mem_cgroup_is_root(memcg)) >> @@ -2742,7 +2749,6 @@ static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages) >> if (do_memsw_account()) >> page_counter_uncharge(&memcg->memsw, nr_pages); >> } >> -#endif >> >> static void commit_charge(struct folio *folio, struct mem_cgroup *memcg) >> { >> -- >> 2.18.1 >>
On Sun, Jan 30, 2022 at 10:55:56PM -0500, Waiman Long wrote: > On 10/1/21 19:51, Roman Gushchin wrote: > > On Fri, Oct 01, 2021 at 03:09:36PM -0400, Waiman Long wrote: > > > When freeing a page associated with an offlined memcg, refill_stock() > > > will put it into local stock delaying its demise until another memcg > > > comes in to take its place in the stock. To avoid that, we now check > > > for offlined memcg and go directly in this case to the slowpath for > > > the uncharge via the repurposed cancel_charge() function. > > Hi Waiman! > > > > I'm afraid it can make a cleanup of a dying cgroup slower: for every > > released page we'll potentially traverse the whole cgroup tree and > > decrease atomic page counters. > > > > I'm not sure I understand the benefits we get from this change which > > do justify the slowdown on the cleanup path. > > > > Thanks! > > I was notified of a lockdep splat that this patch may help to prevent. Would you mind to test this patch: https://www.spinics.net/lists/cgroups/msg31244.html ? It should address this dependency. Thanks!
On 1/31/22 12:01, Roman Gushchin wrote: > On Sun, Jan 30, 2022 at 10:55:56PM -0500, Waiman Long wrote: >> On 10/1/21 19:51, Roman Gushchin wrote: >>> On Fri, Oct 01, 2021 at 03:09:36PM -0400, Waiman Long wrote: >>>> When freeing a page associated with an offlined memcg, refill_stock() >>>> will put it into local stock delaying its demise until another memcg >>>> comes in to take its place in the stock. To avoid that, we now check >>>> for offlined memcg and go directly in this case to the slowpath for >>>> the uncharge via the repurposed cancel_charge() function. >>> Hi Waiman! >>> >>> I'm afraid it can make a cleanup of a dying cgroup slower: for every >>> released page we'll potentially traverse the whole cgroup tree and >>> decrease atomic page counters. >>> >>> I'm not sure I understand the benefits we get from this change which >>> do justify the slowdown on the cleanup path. >>> >>> Thanks! >> I was notified of a lockdep splat that this patch may help to prevent. > Would you mind to test this patch: > https://www.spinics.net/lists/cgroups/msg31244.html ? > > It should address this dependency. Thanks for the pointer. I believe that your patch should be able to address this circular locking dependency. Feel free to add my Reviewed-by: Waiman Long <longman@redhat.com> Cheers, Longman
On 1/31/22 12:09, Waiman Long wrote: > On 1/31/22 12:01, Roman Gushchin wrote: >> On Sun, Jan 30, 2022 at 10:55:56PM -0500, Waiman Long wrote: >>> On 10/1/21 19:51, Roman Gushchin wrote: >>>> On Fri, Oct 01, 2021 at 03:09:36PM -0400, Waiman Long wrote: >>>>> When freeing a page associated with an offlined memcg, refill_stock() >>>>> will put it into local stock delaying its demise until another memcg >>>>> comes in to take its place in the stock. To avoid that, we now check >>>>> for offlined memcg and go directly in this case to the slowpath for >>>>> the uncharge via the repurposed cancel_charge() function. >>>> Hi Waiman! >>>> >>>> I'm afraid it can make a cleanup of a dying cgroup slower: for every >>>> released page we'll potentially traverse the whole cgroup tree and >>>> decrease atomic page counters. >>>> >>>> I'm not sure I understand the benefits we get from this change which >>>> do justify the slowdown on the cleanup path. >>>> >>>> Thanks! >>> I was notified of a lockdep splat that this patch may help to prevent. >> Would you mind to test this patch: >> https://www.spinics.net/lists/cgroups/msg31244.html ? >> >> It should address this dependency. > > Thanks for the pointer. I believe that your patch should be able to > address this circular locking dependency. > > Feel free to add my > > Reviewed-by: Waiman Long <longman@redhat.com> BTW, have you posted it to lkml? If not, would you mind doing so? Thanks, Longman
On Mon, Jan 31, 2022 at 12:09:09PM -0500, Waiman Long wrote: > On 1/31/22 12:01, Roman Gushchin wrote: > > On Sun, Jan 30, 2022 at 10:55:56PM -0500, Waiman Long wrote: > > > On 10/1/21 19:51, Roman Gushchin wrote: > > > > On Fri, Oct 01, 2021 at 03:09:36PM -0400, Waiman Long wrote: > > > > > When freeing a page associated with an offlined memcg, refill_stock() > > > > > will put it into local stock delaying its demise until another memcg > > > > > comes in to take its place in the stock. To avoid that, we now check > > > > > for offlined memcg and go directly in this case to the slowpath for > > > > > the uncharge via the repurposed cancel_charge() function. > > > > Hi Waiman! > > > > > > > > I'm afraid it can make a cleanup of a dying cgroup slower: for every > > > > released page we'll potentially traverse the whole cgroup tree and > > > > decrease atomic page counters. > > > > > > > > I'm not sure I understand the benefits we get from this change which > > > > do justify the slowdown on the cleanup path. > > > > > > > > Thanks! > > > I was notified of a lockdep splat that this patch may help to prevent. > > Would you mind to test this patch: > > https://www.spinics.net/lists/cgroups/msg31244.html ? > > > > It should address this dependency. > > Thanks for the pointer. I believe that your patch should be able to address > this circular locking dependency. > > Feel free to add my > > Reviewed-by: Waiman Long <longman@redhat.com> Thank you!
On Mon, Jan 31, 2022 at 12:15:19PM -0500, Waiman Long wrote: > On 1/31/22 12:09, Waiman Long wrote: > > On 1/31/22 12:01, Roman Gushchin wrote: > > > On Sun, Jan 30, 2022 at 10:55:56PM -0500, Waiman Long wrote: > > > > On 10/1/21 19:51, Roman Gushchin wrote: > > > > > On Fri, Oct 01, 2021 at 03:09:36PM -0400, Waiman Long wrote: > > > > > > When freeing a page associated with an offlined memcg, refill_stock() > > > > > > will put it into local stock delaying its demise until another memcg > > > > > > comes in to take its place in the stock. To avoid that, we now check > > > > > > for offlined memcg and go directly in this case to the slowpath for > > > > > > the uncharge via the repurposed cancel_charge() function. > > > > > Hi Waiman! > > > > > > > > > > I'm afraid it can make a cleanup of a dying cgroup slower: for every > > > > > released page we'll potentially traverse the whole cgroup tree and > > > > > decrease atomic page counters. > > > > > > > > > > I'm not sure I understand the benefits we get from this change which > > > > > do justify the slowdown on the cleanup path. > > > > > > > > > > Thanks! > > > > I was notified of a lockdep splat that this patch may help to prevent. > > > Would you mind to test this patch: > > > https://www.spinics.net/lists/cgroups/msg31244.html ? > > > > > > It should address this dependency. > > > > Thanks for the pointer. I believe that your patch should be able to > > address this circular locking dependency. > > > > Feel free to add my > > > > Reviewed-by: Waiman Long <longman@redhat.com> > > BTW, have you posted it to lkml? If not, would you mind doing so? Not yet. I was waiting for Alexander to confirm that it resolves the originally reported issue. I just pinged him, will wait for tomorrow and post the patch in any case. Thanks!
On 1/31/22 12:19, Roman Gushchin wrote: > On Mon, Jan 31, 2022 at 12:15:19PM -0500, Waiman Long wrote: >> On 1/31/22 12:09, Waiman Long wrote: >>> On 1/31/22 12:01, Roman Gushchin wrote: >>>> On Sun, Jan 30, 2022 at 10:55:56PM -0500, Waiman Long wrote: >>>>> On 10/1/21 19:51, Roman Gushchin wrote: >>>>>> On Fri, Oct 01, 2021 at 03:09:36PM -0400, Waiman Long wrote: >>>>>>> When freeing a page associated with an offlined memcg, refill_stock() >>>>>>> will put it into local stock delaying its demise until another memcg >>>>>>> comes in to take its place in the stock. To avoid that, we now check >>>>>>> for offlined memcg and go directly in this case to the slowpath for >>>>>>> the uncharge via the repurposed cancel_charge() function. >>>>>> Hi Waiman! >>>>>> >>>>>> I'm afraid it can make a cleanup of a dying cgroup slower: for every >>>>>> released page we'll potentially traverse the whole cgroup tree and >>>>>> decrease atomic page counters. >>>>>> >>>>>> I'm not sure I understand the benefits we get from this change which >>>>>> do justify the slowdown on the cleanup path. >>>>>> >>>>>> Thanks! >>>>> I was notified of a lockdep splat that this patch may help to prevent. >>>> Would you mind to test this patch: >>>> https://www.spinics.net/lists/cgroups/msg31244.html ? >>>> >>>> It should address this dependency. >>> Thanks for the pointer. I believe that your patch should be able to >>> address this circular locking dependency. >>> >>> Feel free to add my >>> >>> Reviewed-by: Waiman Long <longman@redhat.com> >> BTW, have you posted it to lkml? If not, would you mind doing so? > Not yet. > > I was waiting for Alexander to confirm that it resolves the originally reported > issue. I just pinged him, will wait for tomorrow and post the patch in any case. > > Thanks! I see. This is not a problem that is easily reproducible. You need to hit the right timing for the lockdep splat to appear. Regards, Longman
On Mon, Jan 31, 2022 at 9:25 AM Waiman Long <longman@redhat.com> wrote: > > On 1/31/22 12:19, Roman Gushchin wrote: > > On Mon, Jan 31, 2022 at 12:15:19PM -0500, Waiman Long wrote: > >> On 1/31/22 12:09, Waiman Long wrote: > >>> On 1/31/22 12:01, Roman Gushchin wrote: > >>>> On Sun, Jan 30, 2022 at 10:55:56PM -0500, Waiman Long wrote: > >>>>> On 10/1/21 19:51, Roman Gushchin wrote: > >>>>>> On Fri, Oct 01, 2021 at 03:09:36PM -0400, Waiman Long wrote: > >>>>>>> When freeing a page associated with an offlined memcg, refill_stock() > >>>>>>> will put it into local stock delaying its demise until another memcg > >>>>>>> comes in to take its place in the stock. To avoid that, we now check > >>>>>>> for offlined memcg and go directly in this case to the slowpath for > >>>>>>> the uncharge via the repurposed cancel_charge() function. > >>>>>> Hi Waiman! > >>>>>> > >>>>>> I'm afraid it can make a cleanup of a dying cgroup slower: for every > >>>>>> released page we'll potentially traverse the whole cgroup tree and > >>>>>> decrease atomic page counters. > >>>>>> > >>>>>> I'm not sure I understand the benefits we get from this change which > >>>>>> do justify the slowdown on the cleanup path. > >>>>>> > >>>>>> Thanks! > >>>>> I was notified of a lockdep splat that this patch may help to prevent. > >>>> Would you mind to test this patch: > >>>> https://www.spinics.net/lists/cgroups/msg31244.html ? > >>>> > >>>> It should address this dependency. > >>> Thanks for the pointer. I believe that your patch should be able to > >>> address this circular locking dependency. > >>> > >>> Feel free to add my > >>> > >>> Reviewed-by: Waiman Long <longman@redhat.com> > >> BTW, have you posted it to lkml? If not, would you mind doing so? > > Not yet. > > > > I was waiting for Alexander to confirm that it resolves the originally reported > > issue. I just pinged him, will wait for tomorrow and post the patch in any case. > > > > Thanks! > > I see. This is not a problem that is easily reproducible. You need to > hit the right timing for the lockdep splat to appear. I agree here. The patch on its own has merits as it is reducing dependency on an unrelated lock.
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 4b32896d87a2..4568363062c1 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2167,6 +2167,8 @@ static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages) return ret; } +static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages); + /* * Returns stocks cached in percpu and reset cached information. */ @@ -2178,9 +2180,7 @@ static void drain_stock(struct memcg_stock_pcp *stock) return; if (stock->nr_pages) { - page_counter_uncharge(&old->memory, stock->nr_pages); - if (do_memsw_account()) - page_counter_uncharge(&old->memsw, stock->nr_pages); + cancel_charge(old, stock->nr_pages); stock->nr_pages = 0; } @@ -2219,6 +2219,14 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) struct memcg_stock_pcp *stock; unsigned long flags; + /* + * An offlined memcg shouldn't be put into stock. + */ + if (unlikely(memcg->kmem_state != KMEM_ONLINE)) { + cancel_charge(memcg, nr_pages); + return; + } + local_irq_save(flags); stock = this_cpu_ptr(&memcg_stock); @@ -2732,7 +2740,6 @@ static inline int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, return try_charge_memcg(memcg, gfp_mask, nr_pages); } -#if defined(CONFIG_MEMCG_KMEM) || defined(CONFIG_MMU) static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages) { if (mem_cgroup_is_root(memcg)) @@ -2742,7 +2749,6 @@ static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages) if (do_memsw_account()) page_counter_uncharge(&memcg->memsw, nr_pages); } -#endif static void commit_charge(struct folio *folio, struct mem_cgroup *memcg) {
When freeing a page associated with an offlined memcg, refill_stock() will put it into local stock delaying its demise until another memcg comes in to take its place in the stock. To avoid that, we now check for offlined memcg and go directly in this case to the slowpath for the uncharge via the repurposed cancel_charge() function. Signed-off-by: Waiman Long <longman@redhat.com> --- mm/memcontrol.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-)