* [PATCH 0/3] mm, memcg: Miscellaneous cleanups
@ 2021-10-01 19:09 Waiman Long
2021-10-01 19:09 ` [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock Waiman Long
` (2 more replies)
0 siblings, 3 replies; 20+ messages in thread
From: Waiman Long @ 2021-10-01 19:09 UTC (permalink / raw)
To: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton,
Vlastimil Babka, Roman Gushchin
Cc: linux-kernel, cgroups, linux-mm, Shakeel Butt, Muchun Song, Waiman Long
This patch series contains a number of miscellaneous cleanup for memcg. It
is based on the next-20211001 branch.
Waiman Long (3):
mm, memcg: Don't put offlined memcg into local stock
mm, memcg: Remove obsolete memcg_free_kmem()
mm, memcg: Ensure valid memcg from objcg within a RCU critical section
mm/memcontrol.c | 41 +++++++++++++++++++++--------------------
1 file changed, 21 insertions(+), 20 deletions(-)
--
2.18.1
^ permalink raw reply [flat|nested] 20+ messages in thread* [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock 2021-10-01 19:09 [PATCH 0/3] mm, memcg: Miscellaneous cleanups Waiman Long @ 2021-10-01 19:09 ` Waiman Long 2021-10-01 21:17 ` kernel test robot ` (2 more replies) 2021-10-01 19:09 ` [PATCH 2/3] mm, memcg: Remove obsolete memcg_free_kmem() Waiman Long 2021-10-01 19:09 ` [PATCH 3/3] mm, memcg: Ensure valid memcg from objcg within a RCU critical section Waiman Long 2 siblings, 3 replies; 20+ messages in thread From: Waiman Long @ 2021-10-01 19:09 UTC (permalink / raw) To: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, Roman Gushchin Cc: linux-kernel, cgroups, linux-mm, Shakeel Butt, Muchun Song, Waiman Long 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(-) 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 ^ permalink raw reply related [flat|nested] 20+ messages in thread
* Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock 2021-10-01 19:09 ` [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock Waiman Long @ 2021-10-01 21:17 ` kernel test robot 2021-10-01 23:06 ` kernel test robot 2021-10-01 23:51 ` Roman Gushchin 2 siblings, 0 replies; 20+ messages in thread From: kernel test robot @ 2021-10-01 21:17 UTC (permalink / raw) To: Waiman Long, Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, Roman Gushchin Cc: kbuild-all, Linux Memory Management List, linux-kernel, cgroups, Shakeel Butt [-- Attachment #1: Type: text/plain, Size: 3336 bytes --] 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 [-- Attachment #2: .config.gz --] [-- Type: application/gzip, Size: 30314 bytes --] ^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock 2021-10-01 19:09 ` [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock Waiman Long 2021-10-01 21:17 ` kernel test robot @ 2021-10-01 23:06 ` kernel test robot 2021-10-01 23:51 ` Roman Gushchin 2 siblings, 0 replies; 20+ messages in thread From: kernel test robot @ 2021-10-01 23:06 UTC (permalink / raw) To: Waiman Long, Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, Roman Gushchin Cc: llvm, kbuild-all, Linux Memory Management List, linux-kernel, cgroups, Shakeel Butt [-- Attachment #1: Type: text/plain, Size: 2750 bytes --] 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 [-- Attachment #2: .config.gz --] [-- Type: application/gzip, Size: 37965 bytes --] ^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock 2021-10-01 19:09 ` [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock Waiman Long 2021-10-01 21:17 ` kernel test robot 2021-10-01 23:06 ` kernel test robot @ 2021-10-01 23:51 ` Roman Gushchin 2021-10-02 1:54 ` Waiman Long 2022-01-31 3:55 ` Waiman Long 2 siblings, 2 replies; 20+ messages in thread From: Roman Gushchin @ 2021-10-01 23:51 UTC (permalink / raw) To: Waiman Long Cc: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, linux-kernel, cgroups, linux-mm, Shakeel Butt, Muchun Song 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 > ^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock 2021-10-01 23:51 ` Roman Gushchin @ 2021-10-02 1:54 ` Waiman Long 2022-01-31 3:55 ` Waiman Long 1 sibling, 0 replies; 20+ messages in thread From: Waiman Long @ 2021-10-02 1:54 UTC (permalink / raw) To: Roman Gushchin Cc: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, linux-kernel, cgroups, linux-mm, Shakeel Butt, Muchun Song 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 ^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock 2021-10-01 23:51 ` Roman Gushchin 2021-10-02 1:54 ` Waiman Long @ 2022-01-31 3:55 ` Waiman Long 2022-01-31 17:01 ` Roman Gushchin 1 sibling, 1 reply; 20+ messages in thread From: Waiman Long @ 2022-01-31 3:55 UTC (permalink / raw) To: Roman Gushchin Cc: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, linux-kernel, cgroups, linux-mm, Shakeel Butt, Muchun Song 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 >> ^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock 2022-01-31 3:55 ` Waiman Long @ 2022-01-31 17:01 ` Roman Gushchin 2022-01-31 17:09 ` Waiman Long 0 siblings, 1 reply; 20+ messages in thread From: Roman Gushchin @ 2022-01-31 17:01 UTC (permalink / raw) To: Waiman Long Cc: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, linux-kernel, cgroups, linux-mm, Shakeel Butt, Muchun Song 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! ^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock 2022-01-31 17:01 ` Roman Gushchin @ 2022-01-31 17:09 ` Waiman Long 2022-01-31 17:15 ` Waiman Long 2022-01-31 17:15 ` Roman Gushchin 0 siblings, 2 replies; 20+ messages in thread From: Waiman Long @ 2022-01-31 17:09 UTC (permalink / raw) To: Roman Gushchin Cc: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, linux-kernel, cgroups, linux-mm, Shakeel Butt, Muchun Song 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 ^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock 2022-01-31 17:09 ` Waiman Long @ 2022-01-31 17:15 ` Waiman Long 2022-01-31 17:19 ` Roman Gushchin 2022-01-31 17:15 ` Roman Gushchin 1 sibling, 1 reply; 20+ messages in thread From: Waiman Long @ 2022-01-31 17:15 UTC (permalink / raw) To: Roman Gushchin Cc: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, linux-kernel, cgroups, linux-mm, Shakeel Butt, Muchun Song 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 ^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock 2022-01-31 17:15 ` Waiman Long @ 2022-01-31 17:19 ` Roman Gushchin 2022-01-31 17:25 ` Waiman Long 0 siblings, 1 reply; 20+ messages in thread From: Roman Gushchin @ 2022-01-31 17:19 UTC (permalink / raw) To: Waiman Long Cc: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, linux-kernel, cgroups, linux-mm, Shakeel Butt, Muchun Song 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! ^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock 2022-01-31 17:19 ` Roman Gushchin @ 2022-01-31 17:25 ` Waiman Long 2022-01-31 18:00 ` Shakeel Butt 0 siblings, 1 reply; 20+ messages in thread From: Waiman Long @ 2022-01-31 17:25 UTC (permalink / raw) To: Roman Gushchin Cc: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, linux-kernel, cgroups, linux-mm, Shakeel Butt, Muchun Song 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 ^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock 2022-01-31 17:25 ` Waiman Long @ 2022-01-31 18:00 ` Shakeel Butt 0 siblings, 0 replies; 20+ messages in thread From: Shakeel Butt @ 2022-01-31 18:00 UTC (permalink / raw) To: Waiman Long Cc: Roman Gushchin, Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, LKML, Cgroups, Linux MM, Muchun Song 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. ^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock 2022-01-31 17:09 ` Waiman Long 2022-01-31 17:15 ` Waiman Long @ 2022-01-31 17:15 ` Roman Gushchin 1 sibling, 0 replies; 20+ messages in thread From: Roman Gushchin @ 2022-01-31 17:15 UTC (permalink / raw) To: Waiman Long Cc: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, linux-kernel, cgroups, linux-mm, Shakeel Butt, Muchun Song 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! ^ permalink raw reply [flat|nested] 20+ messages in thread
* [PATCH 2/3] mm, memcg: Remove obsolete memcg_free_kmem() 2021-10-01 19:09 [PATCH 0/3] mm, memcg: Miscellaneous cleanups Waiman Long 2021-10-01 19:09 ` [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock Waiman Long @ 2021-10-01 19:09 ` Waiman Long 2021-10-02 0:01 ` Roman Gushchin 2021-10-01 19:09 ` [PATCH 3/3] mm, memcg: Ensure valid memcg from objcg within a RCU critical section Waiman Long 2 siblings, 1 reply; 20+ messages in thread From: Waiman Long @ 2021-10-01 19:09 UTC (permalink / raw) To: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, Roman Gushchin Cc: linux-kernel, cgroups, linux-mm, Shakeel Butt, Muchun Song, Waiman Long Since commit d648bcc7fe65 ("mm: kmem: make memcg_kmem_enabled() irreversible"), the only thing memcg_free_kmem() does is to call memcg_offline_kmem() when the memcg is still online. However, memcg_offline_kmem() is only called from mem_cgroup_css_free() which cannot be reached if the memcg hasn't been offlined first. As this function now serves no purpose, we should just remove it. Signed-off-by: Waiman Long <longman@redhat.com> --- mm/memcontrol.c | 11 ----------- 1 file changed, 11 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 4568363062c1..8177f253a127 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3673,13 +3673,6 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg) memcg_free_cache_id(kmemcg_id); } - -static void memcg_free_kmem(struct mem_cgroup *memcg) -{ - /* css_alloc() failed, offlining didn't happen */ - if (unlikely(memcg->kmem_state == KMEM_ONLINE)) - memcg_offline_kmem(memcg); -} #else static int memcg_online_kmem(struct mem_cgroup *memcg) { @@ -3688,9 +3681,6 @@ static int memcg_online_kmem(struct mem_cgroup *memcg) static void memcg_offline_kmem(struct mem_cgroup *memcg) { } -static void memcg_free_kmem(struct mem_cgroup *memcg) -{ -} #endif /* CONFIG_MEMCG_KMEM */ static int memcg_update_kmem_max(struct mem_cgroup *memcg, @@ -5325,7 +5315,6 @@ static void mem_cgroup_css_free(struct cgroup_subsys_state *css) cancel_work_sync(&memcg->high_work); mem_cgroup_remove_from_trees(memcg); free_shrinker_info(memcg); - memcg_free_kmem(memcg); mem_cgroup_free(memcg); } -- 2.18.1 ^ permalink raw reply related [flat|nested] 20+ messages in thread
* Re: [PATCH 2/3] mm, memcg: Remove obsolete memcg_free_kmem() 2021-10-01 19:09 ` [PATCH 2/3] mm, memcg: Remove obsolete memcg_free_kmem() Waiman Long @ 2021-10-02 0:01 ` Roman Gushchin 2021-10-02 2:03 ` Waiman Long 0 siblings, 1 reply; 20+ messages in thread From: Roman Gushchin @ 2021-10-02 0:01 UTC (permalink / raw) To: Waiman Long Cc: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, linux-kernel, cgroups, linux-mm, Shakeel Butt, Muchun Song On Fri, Oct 01, 2021 at 03:09:37PM -0400, Waiman Long wrote: > Since commit d648bcc7fe65 ("mm: kmem: make memcg_kmem_enabled() > irreversible"), the only thing memcg_free_kmem() does is to call > memcg_offline_kmem() when the memcg is still online. However, > memcg_offline_kmem() is only called from mem_cgroup_css_free() which > cannot be reached if the memcg hasn't been offlined first. Hm, is it true? What if online_css() fails? > As this > function now serves no purpose, we should just remove it. It looks like we can just use memcg_offline_kmem() instead of memcg_free_kmem(). Thanks! > > Signed-off-by: Waiman Long <longman@redhat.com> > --- > mm/memcontrol.c | 11 ----------- > 1 file changed, 11 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 4568363062c1..8177f253a127 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3673,13 +3673,6 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg) > > memcg_free_cache_id(kmemcg_id); > } > - > -static void memcg_free_kmem(struct mem_cgroup *memcg) > -{ > - /* css_alloc() failed, offlining didn't happen */ > - if (unlikely(memcg->kmem_state == KMEM_ONLINE)) > - memcg_offline_kmem(memcg); > -} > #else > static int memcg_online_kmem(struct mem_cgroup *memcg) > { > @@ -3688,9 +3681,6 @@ static int memcg_online_kmem(struct mem_cgroup *memcg) > static void memcg_offline_kmem(struct mem_cgroup *memcg) > { > } > -static void memcg_free_kmem(struct mem_cgroup *memcg) > -{ > -} > #endif /* CONFIG_MEMCG_KMEM */ > > static int memcg_update_kmem_max(struct mem_cgroup *memcg, > @@ -5325,7 +5315,6 @@ static void mem_cgroup_css_free(struct cgroup_subsys_state *css) > cancel_work_sync(&memcg->high_work); > mem_cgroup_remove_from_trees(memcg); > free_shrinker_info(memcg); > - memcg_free_kmem(memcg); > mem_cgroup_free(memcg); > } > > -- > 2.18.1 > ^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH 2/3] mm, memcg: Remove obsolete memcg_free_kmem() 2021-10-02 0:01 ` Roman Gushchin @ 2021-10-02 2:03 ` Waiman Long 0 siblings, 0 replies; 20+ messages in thread From: Waiman Long @ 2021-10-02 2:03 UTC (permalink / raw) To: Roman Gushchin Cc: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, linux-kernel, cgroups, linux-mm, Shakeel Butt, Muchun Song On 10/1/21 8:01 PM, Roman Gushchin wrote: > On Fri, Oct 01, 2021 at 03:09:37PM -0400, Waiman Long wrote: >> Since commit d648bcc7fe65 ("mm: kmem: make memcg_kmem_enabled() >> irreversible"), the only thing memcg_free_kmem() does is to call >> memcg_offline_kmem() when the memcg is still online. However, >> memcg_offline_kmem() is only called from mem_cgroup_css_free() which >> cannot be reached if the memcg hasn't been offlined first. > Hm, is it true? What if online_css() fails? I just realize that memcg_online_kmem() is called at css_create(). So yes, if css_online() fails (i.e. ENOMEM), we will need to do memcg_offline_kmem(). >> As this >> function now serves no purpose, we should just remove it. > It looks like we can just use memcg_offline_kmem() instead of > memcg_free_kmem(). Right, memcg_free_kmem() isn't the right name for that. I agree that we should just change mem_cgroup_css_free() to call memcg_offline_kmem() directly. Will update the patch accordingly. Thanks, Longman ^ permalink raw reply [flat|nested] 20+ messages in thread
* [PATCH 3/3] mm, memcg: Ensure valid memcg from objcg within a RCU critical section 2021-10-01 19:09 [PATCH 0/3] mm, memcg: Miscellaneous cleanups Waiman Long 2021-10-01 19:09 ` [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock Waiman Long 2021-10-01 19:09 ` [PATCH 2/3] mm, memcg: Remove obsolete memcg_free_kmem() Waiman Long @ 2021-10-01 19:09 ` Waiman Long 2021-10-01 20:24 ` Shakeel Butt 2 siblings, 1 reply; 20+ messages in thread From: Waiman Long @ 2021-10-01 19:09 UTC (permalink / raw) To: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, Roman Gushchin Cc: linux-kernel, cgroups, linux-mm, Shakeel Butt, Muchun Song, Waiman Long To ensure that a to-be-offlined memcg fetched from objcg remains valid (has non-zero reference count) within a RCU critical section, a synchronize_rcu() call is inserted at the end of memcg_offline_kmem(). With that change, we no longer need to use css_tryget() in get_mem_cgroup_from_objcg() as the final css_put() in css_killed_work_fn() would not have been called yet. The obj_cgroup_uncharge_pages() function is simplifed to perform the whole uncharge operation within a RCU critical section saving a css_get()/css_put() pair. 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 8177f253a127..1dbb37d96e49 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2769,10 +2769,8 @@ static struct mem_cgroup *get_mem_cgroup_from_objcg(struct obj_cgroup *objcg) struct mem_cgroup *memcg; rcu_read_lock(); -retry: memcg = obj_cgroup_memcg(objcg); - if (unlikely(!css_tryget(&memcg->css))) - goto retry; + css_get(&memcg->css); rcu_read_unlock(); return memcg; @@ -2947,13 +2945,14 @@ static void obj_cgroup_uncharge_pages(struct obj_cgroup *objcg, { struct mem_cgroup *memcg; - memcg = get_mem_cgroup_from_objcg(objcg); + rcu_read_lock(); + memcg = obj_cgroup_memcg(objcg); if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) page_counter_uncharge(&memcg->kmem, nr_pages); refill_stock(memcg, nr_pages); - css_put(&memcg->css); + rcu_read_unlock(); } /* @@ -3672,6 +3671,13 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg) memcg_drain_all_list_lrus(kmemcg_id, parent); memcg_free_cache_id(kmemcg_id); + + /* + * To ensure that a to-be-offlined memcg fetched from objcg remains + * valid within a RCU critical section, we need to wait here until + * the a grace period has elapsed. + */ + synchronize_rcu(); } #else static int memcg_online_kmem(struct mem_cgroup *memcg) -- 2.18.1 ^ permalink raw reply related [flat|nested] 20+ messages in thread
* Re: [PATCH 3/3] mm, memcg: Ensure valid memcg from objcg within a RCU critical section 2021-10-01 19:09 ` [PATCH 3/3] mm, memcg: Ensure valid memcg from objcg within a RCU critical section Waiman Long @ 2021-10-01 20:24 ` Shakeel Butt 2021-10-01 20:34 ` Waiman Long 0 siblings, 1 reply; 20+ messages in thread From: Shakeel Butt @ 2021-10-01 20:24 UTC (permalink / raw) To: Waiman Long Cc: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, Roman Gushchin, LKML, Cgroups, Linux MM, Muchun Song On Fri, Oct 1, 2021 at 12:10 PM Waiman Long <longman@redhat.com> wrote: > > To ensure that a to-be-offlined memcg fetched from objcg remains > valid (has non-zero reference count) within a RCU critical section, > a synchronize_rcu() call is inserted at the end of memcg_offline_kmem(). > > With that change, we no longer need to use css_tryget() > in get_mem_cgroup_from_objcg() as the final css_put() in > css_killed_work_fn() would not have been called yet. > > The obj_cgroup_uncharge_pages() function is simplifed to perform > the whole uncharge operation within a RCU critical section saving a > css_get()/css_put() pair. > > 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 8177f253a127..1dbb37d96e49 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2769,10 +2769,8 @@ static struct mem_cgroup *get_mem_cgroup_from_objcg(struct obj_cgroup *objcg) > struct mem_cgroup *memcg; > > rcu_read_lock(); > -retry: > memcg = obj_cgroup_memcg(objcg); > - if (unlikely(!css_tryget(&memcg->css))) > - goto retry; > + css_get(&memcg->css); > rcu_read_unlock(); > > return memcg; > @@ -2947,13 +2945,14 @@ static void obj_cgroup_uncharge_pages(struct obj_cgroup *objcg, > { > struct mem_cgroup *memcg; > > - memcg = get_mem_cgroup_from_objcg(objcg); > + rcu_read_lock(); > + memcg = obj_cgroup_memcg(objcg); > > if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) > page_counter_uncharge(&memcg->kmem, nr_pages); > refill_stock(memcg, nr_pages); > > - css_put(&memcg->css); > + rcu_read_unlock(); > } > > /* > @@ -3672,6 +3671,13 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg) > memcg_drain_all_list_lrus(kmemcg_id, parent); > > memcg_free_cache_id(kmemcg_id); > + > + /* > + * To ensure that a to-be-offlined memcg fetched from objcg remains > + * valid within a RCU critical section, we need to wait here until > + * the a grace period has elapsed. > + */ > + synchronize_rcu(); This is called with cgroup_mutex held from css_offline path and synchronize_rcu() can be very expensive on a busy system, so, this will indirectly impact all the code paths which take cgroup_mutex. > } > #else > static int memcg_online_kmem(struct mem_cgroup *memcg) > -- > 2.18.1 > ^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH 3/3] mm, memcg: Ensure valid memcg from objcg within a RCU critical section 2021-10-01 20:24 ` Shakeel Butt @ 2021-10-01 20:34 ` Waiman Long 0 siblings, 0 replies; 20+ messages in thread From: Waiman Long @ 2021-10-01 20:34 UTC (permalink / raw) To: Shakeel Butt Cc: Johannes Weiner, Michal Hocko, Vladimir Davydov, Andrew Morton, Vlastimil Babka, Roman Gushchin, LKML, Cgroups, Linux MM, Muchun Song On 10/1/21 4:24 PM, Shakeel Butt wrote: > On Fri, Oct 1, 2021 at 12:10 PM Waiman Long <longman@redhat.com> wrote: >> To ensure that a to-be-offlined memcg fetched from objcg remains >> valid (has non-zero reference count) within a RCU critical section, >> a synchronize_rcu() call is inserted at the end of memcg_offline_kmem(). >> >> With that change, we no longer need to use css_tryget() >> in get_mem_cgroup_from_objcg() as the final css_put() in >> css_killed_work_fn() would not have been called yet. >> >> The obj_cgroup_uncharge_pages() function is simplifed to perform >> the whole uncharge operation within a RCU critical section saving a >> css_get()/css_put() pair. >> >> 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 8177f253a127..1dbb37d96e49 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -2769,10 +2769,8 @@ static struct mem_cgroup *get_mem_cgroup_from_objcg(struct obj_cgroup *objcg) >> struct mem_cgroup *memcg; >> >> rcu_read_lock(); >> -retry: >> memcg = obj_cgroup_memcg(objcg); >> - if (unlikely(!css_tryget(&memcg->css))) >> - goto retry; >> + css_get(&memcg->css); >> rcu_read_unlock(); >> >> return memcg; >> @@ -2947,13 +2945,14 @@ static void obj_cgroup_uncharge_pages(struct obj_cgroup *objcg, >> { >> struct mem_cgroup *memcg; >> >> - memcg = get_mem_cgroup_from_objcg(objcg); >> + rcu_read_lock(); >> + memcg = obj_cgroup_memcg(objcg); >> >> if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) >> page_counter_uncharge(&memcg->kmem, nr_pages); >> refill_stock(memcg, nr_pages); >> >> - css_put(&memcg->css); >> + rcu_read_unlock(); >> } >> >> /* >> @@ -3672,6 +3671,13 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg) >> memcg_drain_all_list_lrus(kmemcg_id, parent); >> >> memcg_free_cache_id(kmemcg_id); >> + >> + /* >> + * To ensure that a to-be-offlined memcg fetched from objcg remains >> + * valid within a RCU critical section, we need to wait here until >> + * the a grace period has elapsed. >> + */ >> + synchronize_rcu(); > This is called with cgroup_mutex held from css_offline path and > synchronize_rcu() can be very expensive on a busy system, so, this > will indirectly impact all the code paths which take cgroup_mutex. > Yes, you are right. Just don't consider this patch for the time being. I will need to find a way to work around that. Thanks, Longman ^ permalink raw reply [flat|nested] 20+ messages in thread
end of thread, other threads:[~2022-01-31 18:00 UTC | newest] Thread overview: 20+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-10-01 19:09 [PATCH 0/3] mm, memcg: Miscellaneous cleanups Waiman Long 2021-10-01 19:09 ` [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock Waiman Long 2021-10-01 21:17 ` kernel test robot 2021-10-01 23:06 ` kernel test robot 2021-10-01 23:51 ` Roman Gushchin 2021-10-02 1:54 ` Waiman Long 2022-01-31 3:55 ` Waiman Long 2022-01-31 17:01 ` Roman Gushchin 2022-01-31 17:09 ` Waiman Long 2022-01-31 17:15 ` Waiman Long 2022-01-31 17:19 ` Roman Gushchin 2022-01-31 17:25 ` Waiman Long 2022-01-31 18:00 ` Shakeel Butt 2022-01-31 17:15 ` Roman Gushchin 2021-10-01 19:09 ` [PATCH 2/3] mm, memcg: Remove obsolete memcg_free_kmem() Waiman Long 2021-10-02 0:01 ` Roman Gushchin 2021-10-02 2:03 ` Waiman Long 2021-10-01 19:09 ` [PATCH 3/3] mm, memcg: Ensure valid memcg from objcg within a RCU critical section Waiman Long 2021-10-01 20:24 ` Shakeel Butt 2021-10-01 20:34 ` Waiman Long
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