Re: [PATCH v7 REBASED 00/17] Improve shrink_slab() scalability (old complexity was O(n^2), new is O(n))
On Mon, 2 Jul 2018 12:10:47 +0300 Kirill Tkhai wrote: > Hi, Andrew, > > this series is made on top of 4.18-rc1, while now I see > "mm-list_lru-add-lock_irq-member-to-__list_lru_init.patch" > in mm tree, which conflicts with two of patches from series. Well, "mm: use irq locking suffix instead local_irq_disable()" is a fairly straightforward cleanup series, so it would be best to base your patches on that work, please. There is a significant review comment from Vladimir against "mm: list_lru: add lock_irq member to __list_lru_init()" to which Sebastian has yet to respond (please). > Should I rebase the series on top of current mm tree? What are you plans on > this series? It looks like they're ready for an initial merge.
Re: [PATCH v7 REBASED 00/17] Improve shrink_slab() scalability (old complexity was O(n^2), new is O(n))
On Mon, 2 Jul 2018 12:10:47 +0300 Kirill Tkhai wrote: > Hi, Andrew, > > this series is made on top of 4.18-rc1, while now I see > "mm-list_lru-add-lock_irq-member-to-__list_lru_init.patch" > in mm tree, which conflicts with two of patches from series. Well, "mm: use irq locking suffix instead local_irq_disable()" is a fairly straightforward cleanup series, so it would be best to base your patches on that work, please. There is a significant review comment from Vladimir against "mm: list_lru: add lock_irq member to __list_lru_init()" to which Sebastian has yet to respond (please). > Should I rebase the series on top of current mm tree? What are you plans on > this series? It looks like they're ready for an initial merge.
Re: [PATCH v7 REBASED 00/17] Improve shrink_slab() scalability (old complexity was O(n^2), new is O(n))
Hi, Andrew, this series is made on top of 4.18-rc1, while now I see "mm-list_lru-add-lock_irq-member-to-__list_lru_init.patch" in mm tree, which conflicts with two of patches from series. Should I rebase the series on top of current mm tree? What are you plans on this series? Strange thing, I didn't add you to CC :( Please, say what should I do. Thanks, Kirill On 18.06.2018 12:44, Kirill Tkhai wrote: > Hi, > > this patches solves the problem with slow shrink_slab() occuring > on the machines having many shrinkers and memory cgroups (i.e., > with many containers). The problem is complexity of shrink_slab() > is O(n^2) and it grows too fast with the growth of containers > numbers. > > Let we have 200 containers, and every container has 10 mounts > and 10 cgroups. All container tasks are isolated, and they don't > touch foreign containers mounts. > > In case of global reclaim, a task has to iterate all over the memcgs > and to call all the memcg-aware shrinkers for all of them. This means, > the task has to visit 200 * 10 = 2000 shrinkers for every memcg, > and since there are 2000 memcgs, the total calls of do_shrink_slab() > are 2000 * 2000 = 400. > > 4 million calls are not a number operations, which can takes 1 cpu cycle. > E.g., super_cache_count() accesses at least two lists, and makes arifmetical > calculations. Even, if there are no charged objects, we do these calculations, > and replaces cpu caches by read memory. I observed nodes spending almost 100% > time in kernel, in case of intensive writing and global reclaim. The writer > consumes pages fast, but it's need to shrink_slab() before the reclaimer > reached shrink pages function (and frees SWAP_CLUSTER_MAX pages). Even if > there is no writing, the iterations just waste the time, and slows reclaim > down. > > Let's see the small test below: > > $echo 1 > /sys/fs/cgroup/memory/memory.use_hierarchy > $mkdir /sys/fs/cgroup/memory/ct > $echo 4000M > /sys/fs/cgroup/memory/ct/memory.kmem.limit_in_bytes > $for i in `seq 0 4000`; > do mkdir /sys/fs/cgroup/memory/ct/$i; > echo $$ > /sys/fs/cgroup/memory/ct/$i/cgroup.procs; > mkdir -p s/$i; mount -t tmpfs $i s/$i; touch s/$i/file; > done > > Then, let's see drop caches time (5 sequential calls): > $time echo 3 > /proc/sys/vm/drop_caches > > 0.00user 13.78system 0:13.78elapsed 99%CPU > 0.00user 5.59system 0:05.60elapsed 99%CPU > 0.00user 5.48system 0:05.48elapsed 99%CPU > 0.00user 8.35system 0:08.35elapsed 99%CPU > 0.00user 8.34system 0:08.35elapsed 99%CPU > > > Last four calls don't actually shrink something. So, the iterations > over slab shrinkers take 5.48 seconds. Not so good for scalability. > > The patchset solves the problem by making shrink_slab() of O(n) > complexity. There are following functional actions: > > 1)Assign id to every registered memcg-aware shrinker. > 2)Maintain per-memcgroup bitmap of memcg-aware shrinkers, > and set a shrinker-related bit after the first element > is added to lru list (also, when removed child memcg > elements are reparanted). > 3)Split memcg-aware shrinkers and !memcg-aware shrinkers, > and call a shrinker if its bit is set in memcg's shrinker > bitmap. > (Also, there is a functionality to clear the bit, after > last element is shrinked). > > This gives signify performance increase. The result after patchset is applied: > > $time echo 3 > /proc/sys/vm/drop_caches > > 0.00user 1.10system 0:01.10elapsed 99%CPU > 0.00user 0.00system 0:00.01elapsed 64%CPU > 0.00user 0.01system 0:00.01elapsed 82%CPU > 0.00user 0.00system 0:00.01elapsed 64%CPU > 0.00user 0.01system 0:00.01elapsed 82%CPU > > The results show the performance increases at least in 548 times. > > So, the patchset makes shrink_slab() of less complexity and improves > the performance in such types of load I pointed. This will give a profit > in case of !global reclaim case, since there also will be less > do_shrink_slab() calls. > > v7: Refactorings and readability improvements. > REBASED on 4.18-rc1 > > v6: Added missed rcu_dereference() to memcg_set_shrinker_bit(). > Use different functions for allocation and expanding map. > Use new memcg_shrinker_map_size variable in memcontrol.c. > Refactorings. > > v5: Make the optimizing logic under CONFIG_MEMCG_SHRINKER instead of MEMCG && > !SLOB > > v4: Do not use memcg mem_cgroup_idr for iteration over mem cgroups > > v3: Many changes requested in commentaries to v2: > > 1)rebase on prealloc_shrinker() code base > 2)root_mem_cgroup is made out of memcg maps > 3)rwsem replaced with shrinkers_nr_max_mutex > 4)changes around assignment of shrinker id to list lru > 5)everything renamed > > v2: Many changes requested in commentaries to v1: > > 1)the code mostly moved to mm/memcontrol.c; > 2)using IDR instead of array of shrinkers; > 3)added a possibility to assign list_lru shrinker id > at the time of shrinker registering; > 4)reorginized locking and renamed functions and
Re: [PATCH v7 REBASED 00/17] Improve shrink_slab() scalability (old complexity was O(n^2), new is O(n))
Hi, Andrew, this series is made on top of 4.18-rc1, while now I see "mm-list_lru-add-lock_irq-member-to-__list_lru_init.patch" in mm tree, which conflicts with two of patches from series. Should I rebase the series on top of current mm tree? What are you plans on this series? Strange thing, I didn't add you to CC :( Please, say what should I do. Thanks, Kirill On 18.06.2018 12:44, Kirill Tkhai wrote: > Hi, > > this patches solves the problem with slow shrink_slab() occuring > on the machines having many shrinkers and memory cgroups (i.e., > with many containers). The problem is complexity of shrink_slab() > is O(n^2) and it grows too fast with the growth of containers > numbers. > > Let we have 200 containers, and every container has 10 mounts > and 10 cgroups. All container tasks are isolated, and they don't > touch foreign containers mounts. > > In case of global reclaim, a task has to iterate all over the memcgs > and to call all the memcg-aware shrinkers for all of them. This means, > the task has to visit 200 * 10 = 2000 shrinkers for every memcg, > and since there are 2000 memcgs, the total calls of do_shrink_slab() > are 2000 * 2000 = 400. > > 4 million calls are not a number operations, which can takes 1 cpu cycle. > E.g., super_cache_count() accesses at least two lists, and makes arifmetical > calculations. Even, if there are no charged objects, we do these calculations, > and replaces cpu caches by read memory. I observed nodes spending almost 100% > time in kernel, in case of intensive writing and global reclaim. The writer > consumes pages fast, but it's need to shrink_slab() before the reclaimer > reached shrink pages function (and frees SWAP_CLUSTER_MAX pages). Even if > there is no writing, the iterations just waste the time, and slows reclaim > down. > > Let's see the small test below: > > $echo 1 > /sys/fs/cgroup/memory/memory.use_hierarchy > $mkdir /sys/fs/cgroup/memory/ct > $echo 4000M > /sys/fs/cgroup/memory/ct/memory.kmem.limit_in_bytes > $for i in `seq 0 4000`; > do mkdir /sys/fs/cgroup/memory/ct/$i; > echo $$ > /sys/fs/cgroup/memory/ct/$i/cgroup.procs; > mkdir -p s/$i; mount -t tmpfs $i s/$i; touch s/$i/file; > done > > Then, let's see drop caches time (5 sequential calls): > $time echo 3 > /proc/sys/vm/drop_caches > > 0.00user 13.78system 0:13.78elapsed 99%CPU > 0.00user 5.59system 0:05.60elapsed 99%CPU > 0.00user 5.48system 0:05.48elapsed 99%CPU > 0.00user 8.35system 0:08.35elapsed 99%CPU > 0.00user 8.34system 0:08.35elapsed 99%CPU > > > Last four calls don't actually shrink something. So, the iterations > over slab shrinkers take 5.48 seconds. Not so good for scalability. > > The patchset solves the problem by making shrink_slab() of O(n) > complexity. There are following functional actions: > > 1)Assign id to every registered memcg-aware shrinker. > 2)Maintain per-memcgroup bitmap of memcg-aware shrinkers, > and set a shrinker-related bit after the first element > is added to lru list (also, when removed child memcg > elements are reparanted). > 3)Split memcg-aware shrinkers and !memcg-aware shrinkers, > and call a shrinker if its bit is set in memcg's shrinker > bitmap. > (Also, there is a functionality to clear the bit, after > last element is shrinked). > > This gives signify performance increase. The result after patchset is applied: > > $time echo 3 > /proc/sys/vm/drop_caches > > 0.00user 1.10system 0:01.10elapsed 99%CPU > 0.00user 0.00system 0:00.01elapsed 64%CPU > 0.00user 0.01system 0:00.01elapsed 82%CPU > 0.00user 0.00system 0:00.01elapsed 64%CPU > 0.00user 0.01system 0:00.01elapsed 82%CPU > > The results show the performance increases at least in 548 times. > > So, the patchset makes shrink_slab() of less complexity and improves > the performance in such types of load I pointed. This will give a profit > in case of !global reclaim case, since there also will be less > do_shrink_slab() calls. > > v7: Refactorings and readability improvements. > REBASED on 4.18-rc1 > > v6: Added missed rcu_dereference() to memcg_set_shrinker_bit(). > Use different functions for allocation and expanding map. > Use new memcg_shrinker_map_size variable in memcontrol.c. > Refactorings. > > v5: Make the optimizing logic under CONFIG_MEMCG_SHRINKER instead of MEMCG && > !SLOB > > v4: Do not use memcg mem_cgroup_idr for iteration over mem cgroups > > v3: Many changes requested in commentaries to v2: > > 1)rebase on prealloc_shrinker() code base > 2)root_mem_cgroup is made out of memcg maps > 3)rwsem replaced with shrinkers_nr_max_mutex > 4)changes around assignment of shrinker id to list lru > 5)everything renamed > > v2: Many changes requested in commentaries to v1: > > 1)the code mostly moved to mm/memcontrol.c; > 2)using IDR instead of array of shrinkers; > 3)added a possibility to assign list_lru shrinker id > at the time of shrinker registering; > 4)reorginized locking and renamed functions and
[PATCH v7 REBASED 00/17] Improve shrink_slab() scalability (old complexity was O(n^2), new is O(n))
Hi,
this patches solves the problem with slow shrink_slab() occuring
on the machines having many shrinkers and memory cgroups (i.e.,
with many containers). The problem is complexity of shrink_slab()
is O(n^2) and it grows too fast with the growth of containers
numbers.
Let we have 200 containers, and every container has 10 mounts
and 10 cgroups. All container tasks are isolated, and they don't
touch foreign containers mounts.
In case of global reclaim, a task has to iterate all over the memcgs
and to call all the memcg-aware shrinkers for all of them. This means,
the task has to visit 200 * 10 = 2000 shrinkers for every memcg,
and since there are 2000 memcgs, the total calls of do_shrink_slab()
are 2000 * 2000 = 400.
4 million calls are not a number operations, which can takes 1 cpu cycle.
E.g., super_cache_count() accesses at least two lists, and makes arifmetical
calculations. Even, if there are no charged objects, we do these calculations,
and replaces cpu caches by read memory. I observed nodes spending almost 100%
time in kernel, in case of intensive writing and global reclaim. The writer
consumes pages fast, but it's need to shrink_slab() before the reclaimer
reached shrink pages function (and frees SWAP_CLUSTER_MAX pages). Even if
there is no writing, the iterations just waste the time, and slows reclaim down.
Let's see the small test below:
$echo 1 > /sys/fs/cgroup/memory/memory.use_hierarchy
$mkdir /sys/fs/cgroup/memory/ct
$echo 4000M > /sys/fs/cgroup/memory/ct/memory.kmem.limit_in_bytes
$for i in `seq 0 4000`;
do mkdir /sys/fs/cgroup/memory/ct/$i;
echo $$ > /sys/fs/cgroup/memory/ct/$i/cgroup.procs;
mkdir -p s/$i; mount -t tmpfs $i s/$i; touch s/$i/file;
done
Then, let's see drop caches time (5 sequential calls):
$time echo 3 > /proc/sys/vm/drop_caches
0.00user 13.78system 0:13.78elapsed 99%CPU
0.00user 5.59system 0:05.60elapsed 99%CPU
0.00user 5.48system 0:05.48elapsed 99%CPU
0.00user 8.35system 0:08.35elapsed 99%CPU
0.00user 8.34system 0:08.35elapsed 99%CPU
Last four calls don't actually shrink something. So, the iterations
over slab shrinkers take 5.48 seconds. Not so good for scalability.
The patchset solves the problem by making shrink_slab() of O(n)
complexity. There are following functional actions:
1)Assign id to every registered memcg-aware shrinker.
2)Maintain per-memcgroup bitmap of memcg-aware shrinkers,
and set a shrinker-related bit after the first element
is added to lru list (also, when removed child memcg
elements are reparanted).
3)Split memcg-aware shrinkers and !memcg-aware shrinkers,
and call a shrinker if its bit is set in memcg's shrinker
bitmap.
(Also, there is a functionality to clear the bit, after
last element is shrinked).
This gives signify performance increase. The result after patchset is applied:
$time echo 3 > /proc/sys/vm/drop_caches
0.00user 1.10system 0:01.10elapsed 99%CPU
0.00user 0.00system 0:00.01elapsed 64%CPU
0.00user 0.01system 0:00.01elapsed 82%CPU
0.00user 0.00system 0:00.01elapsed 64%CPU
0.00user 0.01system 0:00.01elapsed 82%CPU
The results show the performance increases at least in 548 times.
So, the patchset makes shrink_slab() of less complexity and improves
the performance in such types of load I pointed. This will give a profit
in case of !global reclaim case, since there also will be less
do_shrink_slab() calls.
v7: Refactorings and readability improvements.
REBASED on 4.18-rc1
v6: Added missed rcu_dereference() to memcg_set_shrinker_bit().
Use different functions for allocation and expanding map.
Use new memcg_shrinker_map_size variable in memcontrol.c.
Refactorings.
v5: Make the optimizing logic under CONFIG_MEMCG_SHRINKER instead of MEMCG &&
!SLOB
v4: Do not use memcg mem_cgroup_idr for iteration over mem cgroups
v3: Many changes requested in commentaries to v2:
1)rebase on prealloc_shrinker() code base
2)root_mem_cgroup is made out of memcg maps
3)rwsem replaced with shrinkers_nr_max_mutex
4)changes around assignment of shrinker id to list lru
5)everything renamed
v2: Many changes requested in commentaries to v1:
1)the code mostly moved to mm/memcontrol.c;
2)using IDR instead of array of shrinkers;
3)added a possibility to assign list_lru shrinker id
at the time of shrinker registering;
4)reorginized locking and renamed functions and variables.
---
Kirill Tkhai (16):
list_lru: Combine code under the same define
mm: Introduce CONFIG_MEMCG_KMEM as combination of CONFIG_MEMCG &&
!CONFIG_SLOB
mm: Assign id to every memcg-aware shrinker
memcg: Move up for_each_mem_cgroup{,_tree} defines
mm: Assign memcg-aware shrinkers bitmap to memcg
mm: Refactoring in workingset_init()
fs: Refactoring in alloc_super()
fs: Propagate shrinker::id to list_lru
list_lru: Add memcg argument to list_lru_from_kmem()
list_lru: Pass dst_memcg argument to memcg_drain_list_lru_node()
list_lru: Pass lru argument to
[PATCH v7 REBASED 00/17] Improve shrink_slab() scalability (old complexity was O(n^2), new is O(n))
Hi,
this patches solves the problem with slow shrink_slab() occuring
on the machines having many shrinkers and memory cgroups (i.e.,
with many containers). The problem is complexity of shrink_slab()
is O(n^2) and it grows too fast with the growth of containers
numbers.
Let we have 200 containers, and every container has 10 mounts
and 10 cgroups. All container tasks are isolated, and they don't
touch foreign containers mounts.
In case of global reclaim, a task has to iterate all over the memcgs
and to call all the memcg-aware shrinkers for all of them. This means,
the task has to visit 200 * 10 = 2000 shrinkers for every memcg,
and since there are 2000 memcgs, the total calls of do_shrink_slab()
are 2000 * 2000 = 400.
4 million calls are not a number operations, which can takes 1 cpu cycle.
E.g., super_cache_count() accesses at least two lists, and makes arifmetical
calculations. Even, if there are no charged objects, we do these calculations,
and replaces cpu caches by read memory. I observed nodes spending almost 100%
time in kernel, in case of intensive writing and global reclaim. The writer
consumes pages fast, but it's need to shrink_slab() before the reclaimer
reached shrink pages function (and frees SWAP_CLUSTER_MAX pages). Even if
there is no writing, the iterations just waste the time, and slows reclaim down.
Let's see the small test below:
$echo 1 > /sys/fs/cgroup/memory/memory.use_hierarchy
$mkdir /sys/fs/cgroup/memory/ct
$echo 4000M > /sys/fs/cgroup/memory/ct/memory.kmem.limit_in_bytes
$for i in `seq 0 4000`;
do mkdir /sys/fs/cgroup/memory/ct/$i;
echo $$ > /sys/fs/cgroup/memory/ct/$i/cgroup.procs;
mkdir -p s/$i; mount -t tmpfs $i s/$i; touch s/$i/file;
done
Then, let's see drop caches time (5 sequential calls):
$time echo 3 > /proc/sys/vm/drop_caches
0.00user 13.78system 0:13.78elapsed 99%CPU
0.00user 5.59system 0:05.60elapsed 99%CPU
0.00user 5.48system 0:05.48elapsed 99%CPU
0.00user 8.35system 0:08.35elapsed 99%CPU
0.00user 8.34system 0:08.35elapsed 99%CPU
Last four calls don't actually shrink something. So, the iterations
over slab shrinkers take 5.48 seconds. Not so good for scalability.
The patchset solves the problem by making shrink_slab() of O(n)
complexity. There are following functional actions:
1)Assign id to every registered memcg-aware shrinker.
2)Maintain per-memcgroup bitmap of memcg-aware shrinkers,
and set a shrinker-related bit after the first element
is added to lru list (also, when removed child memcg
elements are reparanted).
3)Split memcg-aware shrinkers and !memcg-aware shrinkers,
and call a shrinker if its bit is set in memcg's shrinker
bitmap.
(Also, there is a functionality to clear the bit, after
last element is shrinked).
This gives signify performance increase. The result after patchset is applied:
$time echo 3 > /proc/sys/vm/drop_caches
0.00user 1.10system 0:01.10elapsed 99%CPU
0.00user 0.00system 0:00.01elapsed 64%CPU
0.00user 0.01system 0:00.01elapsed 82%CPU
0.00user 0.00system 0:00.01elapsed 64%CPU
0.00user 0.01system 0:00.01elapsed 82%CPU
The results show the performance increases at least in 548 times.
So, the patchset makes shrink_slab() of less complexity and improves
the performance in such types of load I pointed. This will give a profit
in case of !global reclaim case, since there also will be less
do_shrink_slab() calls.
v7: Refactorings and readability improvements.
REBASED on 4.18-rc1
v6: Added missed rcu_dereference() to memcg_set_shrinker_bit().
Use different functions for allocation and expanding map.
Use new memcg_shrinker_map_size variable in memcontrol.c.
Refactorings.
v5: Make the optimizing logic under CONFIG_MEMCG_SHRINKER instead of MEMCG &&
!SLOB
v4: Do not use memcg mem_cgroup_idr for iteration over mem cgroups
v3: Many changes requested in commentaries to v2:
1)rebase on prealloc_shrinker() code base
2)root_mem_cgroup is made out of memcg maps
3)rwsem replaced with shrinkers_nr_max_mutex
4)changes around assignment of shrinker id to list lru
5)everything renamed
v2: Many changes requested in commentaries to v1:
1)the code mostly moved to mm/memcontrol.c;
2)using IDR instead of array of shrinkers;
3)added a possibility to assign list_lru shrinker id
at the time of shrinker registering;
4)reorginized locking and renamed functions and variables.
---
Kirill Tkhai (16):
list_lru: Combine code under the same define
mm: Introduce CONFIG_MEMCG_KMEM as combination of CONFIG_MEMCG &&
!CONFIG_SLOB
mm: Assign id to every memcg-aware shrinker
memcg: Move up for_each_mem_cgroup{,_tree} defines
mm: Assign memcg-aware shrinkers bitmap to memcg
mm: Refactoring in workingset_init()
fs: Refactoring in alloc_super()
fs: Propagate shrinker::id to list_lru
list_lru: Add memcg argument to list_lru_from_kmem()
list_lru: Pass dst_memcg argument to memcg_drain_list_lru_node()
list_lru: Pass lru argument to
[PATCH v7 REBASED 00/17] Improve shrink_slab() scalability (old complexity was O(n^2), new is O(n))
Hi,
this patches solves the problem with slow shrink_slab() occuring
on the machines having many shrinkers and memory cgroups (i.e.,
with many containers). The problem is complexity of shrink_slab()
is O(n^2) and it grows too fast with the growth of containers
numbers.
Let we have 200 containers, and every container has 10 mounts
and 10 cgroups. All container tasks are isolated, and they don't
touch foreign containers mounts.
In case of global reclaim, a task has to iterate all over the memcgs
and to call all the memcg-aware shrinkers for all of them. This means,
the task has to visit 200 * 10 = 2000 shrinkers for every memcg,
and since there are 2000 memcgs, the total calls of do_shrink_slab()
are 2000 * 2000 = 400.
4 million calls are not a number operations, which can takes 1 cpu cycle.
E.g., super_cache_count() accesses at least two lists, and makes arifmetical
calculations. Even, if there are no charged objects, we do these calculations,
and replaces cpu caches by read memory. I observed nodes spending almost 100%
time in kernel, in case of intensive writing and global reclaim. The writer
consumes pages fast, but it's need to shrink_slab() before the reclaimer
reached shrink pages function (and frees SWAP_CLUSTER_MAX pages). Even if
there is no writing, the iterations just waste the time, and slows reclaim down.
Let's see the small test below:
$echo 1 > /sys/fs/cgroup/memory/memory.use_hierarchy
$mkdir /sys/fs/cgroup/memory/ct
$echo 4000M > /sys/fs/cgroup/memory/ct/memory.kmem.limit_in_bytes
$for i in `seq 0 4000`;
do mkdir /sys/fs/cgroup/memory/ct/$i;
echo $$ > /sys/fs/cgroup/memory/ct/$i/cgroup.procs;
mkdir -p s/$i; mount -t tmpfs $i s/$i; touch s/$i/file;
done
Then, let's see drop caches time (5 sequential calls):
$time echo 3 > /proc/sys/vm/drop_caches
0.00user 13.78system 0:13.78elapsed 99%CPU
0.00user 5.59system 0:05.60elapsed 99%CPU
0.00user 5.48system 0:05.48elapsed 99%CPU
0.00user 8.35system 0:08.35elapsed 99%CPU
0.00user 8.34system 0:08.35elapsed 99%CPU
Last four calls don't actually shrink something. So, the iterations
over slab shrinkers take 5.48 seconds. Not so good for scalability.
The patchset solves the problem by making shrink_slab() of O(n)
complexity. There are following functional actions:
1)Assign id to every registered memcg-aware shrinker.
2)Maintain per-memcgroup bitmap of memcg-aware shrinkers,
and set a shrinker-related bit after the first element
is added to lru list (also, when removed child memcg
elements are reparanted).
3)Split memcg-aware shrinkers and !memcg-aware shrinkers,
and call a shrinker if its bit is set in memcg's shrinker
bitmap.
(Also, there is a functionality to clear the bit, after
last element is shrinked).
This gives signify performance increase. The result after patchset is applied:
$time echo 3 > /proc/sys/vm/drop_caches
0.00user 1.10system 0:01.10elapsed 99%CPU
0.00user 0.00system 0:00.01elapsed 64%CPU
0.00user 0.01system 0:00.01elapsed 82%CPU
0.00user 0.00system 0:00.01elapsed 64%CPU
0.00user 0.01system 0:00.01elapsed 82%CPU
The results show the performance increases at least in 548 times.
So, the patchset makes shrink_slab() of less complexity and improves
the performance in such types of load I pointed. This will give a profit
in case of !global reclaim case, since there also will be less
do_shrink_slab() calls.
v7: Refactorings and readability improvements.
REBASED on 4.18-rc1
v6: Added missed rcu_dereference() to memcg_set_shrinker_bit().
Use different functions for allocation and expanding map.
Use new memcg_shrinker_map_size variable in memcontrol.c.
Refactorings.
v5: Make the optimizing logic under CONFIG_MEMCG_SHRINKER instead of MEMCG &&
!SLOB
v4: Do not use memcg mem_cgroup_idr for iteration over mem cgroups
v3: Many changes requested in commentaries to v2:
1)rebase on prealloc_shrinker() code base
2)root_mem_cgroup is made out of memcg maps
3)rwsem replaced with shrinkers_nr_max_mutex
4)changes around assignment of shrinker id to list lru
5)everything renamed
v2: Many changes requested in commentaries to v1:
1)the code mostly moved to mm/memcontrol.c;
2)using IDR instead of array of shrinkers;
3)added a possibility to assign list_lru shrinker id
at the time of shrinker registering;
4)reorginized locking and renamed functions and variables.
---
Kirill Tkhai (16):
list_lru: Combine code under the same define
mm: Introduce CONFIG_MEMCG_KMEM as combination of CONFIG_MEMCG &&
!CONFIG_SLOB
mm: Assign id to every memcg-aware shrinker
memcg: Move up for_each_mem_cgroup{,_tree} defines
mm: Assign memcg-aware shrinkers bitmap to memcg
mm: Refactoring in workingset_init()
fs: Refactoring in alloc_super()
fs: Propagate shrinker::id to list_lru
list_lru: Add memcg argument to list_lru_from_kmem()
list_lru: Pass dst_memcg argument to memcg_drain_list_lru_node()
list_lru: Pass lru argument to
[PATCH v7 REBASED 00/17] Improve shrink_slab() scalability (old complexity was O(n^2), new is O(n))
Hi,
this patches solves the problem with slow shrink_slab() occuring
on the machines having many shrinkers and memory cgroups (i.e.,
with many containers). The problem is complexity of shrink_slab()
is O(n^2) and it grows too fast with the growth of containers
numbers.
Let we have 200 containers, and every container has 10 mounts
and 10 cgroups. All container tasks are isolated, and they don't
touch foreign containers mounts.
In case of global reclaim, a task has to iterate all over the memcgs
and to call all the memcg-aware shrinkers for all of them. This means,
the task has to visit 200 * 10 = 2000 shrinkers for every memcg,
and since there are 2000 memcgs, the total calls of do_shrink_slab()
are 2000 * 2000 = 400.
4 million calls are not a number operations, which can takes 1 cpu cycle.
E.g., super_cache_count() accesses at least two lists, and makes arifmetical
calculations. Even, if there are no charged objects, we do these calculations,
and replaces cpu caches by read memory. I observed nodes spending almost 100%
time in kernel, in case of intensive writing and global reclaim. The writer
consumes pages fast, but it's need to shrink_slab() before the reclaimer
reached shrink pages function (and frees SWAP_CLUSTER_MAX pages). Even if
there is no writing, the iterations just waste the time, and slows reclaim down.
Let's see the small test below:
$echo 1 > /sys/fs/cgroup/memory/memory.use_hierarchy
$mkdir /sys/fs/cgroup/memory/ct
$echo 4000M > /sys/fs/cgroup/memory/ct/memory.kmem.limit_in_bytes
$for i in `seq 0 4000`;
do mkdir /sys/fs/cgroup/memory/ct/$i;
echo $$ > /sys/fs/cgroup/memory/ct/$i/cgroup.procs;
mkdir -p s/$i; mount -t tmpfs $i s/$i; touch s/$i/file;
done
Then, let's see drop caches time (5 sequential calls):
$time echo 3 > /proc/sys/vm/drop_caches
0.00user 13.78system 0:13.78elapsed 99%CPU
0.00user 5.59system 0:05.60elapsed 99%CPU
0.00user 5.48system 0:05.48elapsed 99%CPU
0.00user 8.35system 0:08.35elapsed 99%CPU
0.00user 8.34system 0:08.35elapsed 99%CPU
Last four calls don't actually shrink something. So, the iterations
over slab shrinkers take 5.48 seconds. Not so good for scalability.
The patchset solves the problem by making shrink_slab() of O(n)
complexity. There are following functional actions:
1)Assign id to every registered memcg-aware shrinker.
2)Maintain per-memcgroup bitmap of memcg-aware shrinkers,
and set a shrinker-related bit after the first element
is added to lru list (also, when removed child memcg
elements are reparanted).
3)Split memcg-aware shrinkers and !memcg-aware shrinkers,
and call a shrinker if its bit is set in memcg's shrinker
bitmap.
(Also, there is a functionality to clear the bit, after
last element is shrinked).
This gives signify performance increase. The result after patchset is applied:
$time echo 3 > /proc/sys/vm/drop_caches
0.00user 1.10system 0:01.10elapsed 99%CPU
0.00user 0.00system 0:00.01elapsed 64%CPU
0.00user 0.01system 0:00.01elapsed 82%CPU
0.00user 0.00system 0:00.01elapsed 64%CPU
0.00user 0.01system 0:00.01elapsed 82%CPU
The results show the performance increases at least in 548 times.
So, the patchset makes shrink_slab() of less complexity and improves
the performance in such types of load I pointed. This will give a profit
in case of !global reclaim case, since there also will be less
do_shrink_slab() calls.
v7: Refactorings and readability improvements.
REBASED on 4.18-rc1
v6: Added missed rcu_dereference() to memcg_set_shrinker_bit().
Use different functions for allocation and expanding map.
Use new memcg_shrinker_map_size variable in memcontrol.c.
Refactorings.
v5: Make the optimizing logic under CONFIG_MEMCG_SHRINKER instead of MEMCG &&
!SLOB
v4: Do not use memcg mem_cgroup_idr for iteration over mem cgroups
v3: Many changes requested in commentaries to v2:
1)rebase on prealloc_shrinker() code base
2)root_mem_cgroup is made out of memcg maps
3)rwsem replaced with shrinkers_nr_max_mutex
4)changes around assignment of shrinker id to list lru
5)everything renamed
v2: Many changes requested in commentaries to v1:
1)the code mostly moved to mm/memcontrol.c;
2)using IDR instead of array of shrinkers;
3)added a possibility to assign list_lru shrinker id
at the time of shrinker registering;
4)reorginized locking and renamed functions and variables.
---
Kirill Tkhai (16):
list_lru: Combine code under the same define
mm: Introduce CONFIG_MEMCG_KMEM as combination of CONFIG_MEMCG &&
!CONFIG_SLOB
mm: Assign id to every memcg-aware shrinker
memcg: Move up for_each_mem_cgroup{,_tree} defines
mm: Assign memcg-aware shrinkers bitmap to memcg
mm: Refactoring in workingset_init()
fs: Refactoring in alloc_super()
fs: Propagate shrinker::id to list_lru
list_lru: Add memcg argument to list_lru_from_kmem()
list_lru: Pass dst_memcg argument to memcg_drain_list_lru_node()
list_lru: Pass lru argument to
