| Message ID | 20210301062227.59292-1-songmuchun@bytedance.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Use obj_cgroup APIs to change kmem pages | expand |
Hi Muchun! On Mon, Mar 01, 2021 at 02:22:22PM +0800, Muchun Song wrote: > Since Roman series "The new cgroup slab memory controller" applied. All > slab objects are changed via the new APIs of obj_cgroup. This new APIs > introduce a struct obj_cgroup instead of using struct mem_cgroup directly > to charge slab objects. It prevents long-living objects from pinning the > original memory cgroup in the memory. But there are still some corner > objects (e.g. allocations larger than order-1 page on SLUB) which are > not charged via the API of obj_cgroup. Those objects (include the pages > which are allocated from buddy allocator directly) are charged as kmem > pages which still hold a reference to the memory cgroup. Yes, this is a good idea, large kmallocs should be treated the same way as small ones. > > E.g. We know that the kernel stack is charged as kmem pages because the > size of the kernel stack can be greater than 2 pages (e.g. 16KB on x86_64 > or arm64). If we create a thread (suppose the thread stack is charged to > memory cgroup A) and then move it from memory cgroup A to memory cgroup > B. Because the kernel stack of the thread hold a reference to the memory > cgroup A. The thread can pin the memory cgroup A in the memory even if > we remove the cgroup A. If we want to see this scenario by using the > following script. We can see that the system has added 500 dying cgroups. > > #!/bin/bash > > cat /proc/cgroups | grep memory > > cd /sys/fs/cgroup/memory > echo 1 > memory.move_charge_at_immigrate > > for i in range{1..500} > do > mkdir kmem_test > echo $$ > kmem_test/cgroup.procs > sleep 3600 & > echo $$ > cgroup.procs > echo `cat kmem_test/cgroup.procs` > cgroup.procs > rmdir kmem_test > done > > cat /proc/cgroups | grep memory Well, moving processes between cgroups always created a lot of issues and corner cases and this one is definitely not the worst. So this problem looks a bit artificial, unless I'm missing something. But if it doesn't introduce any new performance costs and doesn't make the code more complex, I have nothing against. Btw, can you, please, run the spell-checker on commit logs? There are many typos (starting from the title of the series, I guess), which make the patchset look less appealing. Thank you! > > This patchset aims to make those kmem pages drop the reference to memory > cgroup by using the APIs of obj_cgroup. Finally, we can see that the number > of the dying cgroups will not increase if we run the above test script. > > Patch 1-3 are using obj_cgroup APIs to charge kmem pages. The remote > memory cgroup charing APIs is a mechanism to charge kernel memory to a > given memory cgroup. So I also make it use the APIs of obj_cgroup. > Patch 4-5 are doing this. > > Muchun Song (5): > mm: memcontrol: introduce obj_cgroup_{un}charge_page > mm: memcontrol: make page_memcg{_rcu} only applicable for non-kmem > page > mm: memcontrol: reparent the kmem pages on cgroup removal > mm: memcontrol: move remote memcg charging APIs to CONFIG_MEMCG_KMEM > mm: memcontrol: use object cgroup for remote memory cgroup charging > > fs/buffer.c | 10 +- > fs/notify/fanotify/fanotify.c | 6 +- > fs/notify/fanotify/fanotify_user.c | 2 +- > fs/notify/group.c | 3 +- > fs/notify/inotify/inotify_fsnotify.c | 8 +- > fs/notify/inotify/inotify_user.c | 2 +- > include/linux/bpf.h | 2 +- > include/linux/fsnotify_backend.h | 2 +- > include/linux/memcontrol.h | 109 +++++++++++--- > include/linux/sched.h | 6 +- > include/linux/sched/mm.h | 30 ++-- > kernel/bpf/syscall.c | 35 ++--- > kernel/fork.c | 4 +- > mm/memcontrol.c | 276 ++++++++++++++++++++++------------- > mm/page_alloc.c | 4 +- > 15 files changed, 324 insertions(+), 175 deletions(-) > > -- > 2.11.0 >
On Tue, Mar 2, 2021 at 9:12 AM Roman Gushchin <guro@fb.com> wrote: > > Hi Muchun! > > On Mon, Mar 01, 2021 at 02:22:22PM +0800, Muchun Song wrote: > > Since Roman series "The new cgroup slab memory controller" applied. All > > slab objects are changed via the new APIs of obj_cgroup. This new APIs > > introduce a struct obj_cgroup instead of using struct mem_cgroup directly > > to charge slab objects. It prevents long-living objects from pinning the > > original memory cgroup in the memory. But there are still some corner > > objects (e.g. allocations larger than order-1 page on SLUB) which are > > not charged via the API of obj_cgroup. Those objects (include the pages > > which are allocated from buddy allocator directly) are charged as kmem > > pages which still hold a reference to the memory cgroup. > > Yes, this is a good idea, large kmallocs should be treated the same > way as small ones. > > > > > E.g. We know that the kernel stack is charged as kmem pages because the > > size of the kernel stack can be greater than 2 pages (e.g. 16KB on x86_64 > > or arm64). If we create a thread (suppose the thread stack is charged to > > memory cgroup A) and then move it from memory cgroup A to memory cgroup > > B. Because the kernel stack of the thread hold a reference to the memory > > cgroup A. The thread can pin the memory cgroup A in the memory even if > > we remove the cgroup A. If we want to see this scenario by using the > > following script. We can see that the system has added 500 dying cgroups. > > > > #!/bin/bash > > > > cat /proc/cgroups | grep memory > > > > cd /sys/fs/cgroup/memory > > echo 1 > memory.move_charge_at_immigrate > > > > for i in range{1..500} > > do > > mkdir kmem_test > > echo $$ > kmem_test/cgroup.procs > > sleep 3600 & > > echo $$ > cgroup.procs > > echo `cat kmem_test/cgroup.procs` > cgroup.procs > > rmdir kmem_test > > done > > > > cat /proc/cgroups | grep memory > > Well, moving processes between cgroups always created a lot of issues > and corner cases and this one is definitely not the worst. So this problem > looks a bit artificial, unless I'm missing something. But if it doesn't > introduce any new performance costs and doesn't make the code more complex, > I have nothing against. OK. I just want to show that large kmallocs are charged as kmem pages. So I constructed this test case. > > Btw, can you, please, run the spell-checker on commit logs? There are many > typos (starting from the title of the series, I guess), which make the patchset > look less appealing. Sorry for my poor English. I will do that. Thanks for your suggestions. > > Thank you! > > > > > This patchset aims to make those kmem pages drop the reference to memory > > cgroup by using the APIs of obj_cgroup. Finally, we can see that the number > > of the dying cgroups will not increase if we run the above test script. > > > > Patch 1-3 are using obj_cgroup APIs to charge kmem pages. The remote > > memory cgroup charing APIs is a mechanism to charge kernel memory to a > > given memory cgroup. So I also make it use the APIs of obj_cgroup. > > Patch 4-5 are doing this. > > > > Muchun Song (5): > > mm: memcontrol: introduce obj_cgroup_{un}charge_page > > mm: memcontrol: make page_memcg{_rcu} only applicable for non-kmem > > page > > mm: memcontrol: reparent the kmem pages on cgroup removal > > mm: memcontrol: move remote memcg charging APIs to CONFIG_MEMCG_KMEM > > mm: memcontrol: use object cgroup for remote memory cgroup charging > > > > fs/buffer.c | 10 +- > > fs/notify/fanotify/fanotify.c | 6 +- > > fs/notify/fanotify/fanotify_user.c | 2 +- > > fs/notify/group.c | 3 +- > > fs/notify/inotify/inotify_fsnotify.c | 8 +- > > fs/notify/inotify/inotify_user.c | 2 +- > > include/linux/bpf.h | 2 +- > > include/linux/fsnotify_backend.h | 2 +- > > include/linux/memcontrol.h | 109 +++++++++++--- > > include/linux/sched.h | 6 +- > > include/linux/sched/mm.h | 30 ++-- > > kernel/bpf/syscall.c | 35 ++--- > > kernel/fork.c | 4 +- > > mm/memcontrol.c | 276 ++++++++++++++++++++++------------- > > mm/page_alloc.c | 4 +- > > 15 files changed, 324 insertions(+), 175 deletions(-) > > > > -- > > 2.11.0 > >
Since Roman series "The new cgroup slab memory controller" applied. All slab objects are changed via the new APIs of obj_cgroup. This new APIs introduce a struct obj_cgroup instead of using struct mem_cgroup directly to charge slab objects. It prevents long-living objects from pinning the original memory cgroup in the memory. But there are still some corner objects (e.g. allocations larger than order-1 page on SLUB) which are not charged via the API of obj_cgroup. Those objects (include the pages which are allocated from buddy allocator directly) are charged as kmem pages which still hold a reference to the memory cgroup. E.g. We know that the kernel stack is charged as kmem pages because the size of the kernel stack can be greater than 2 pages (e.g. 16KB on x86_64 or arm64). If we create a thread (suppose the thread stack is charged to memory cgroup A) and then move it from memory cgroup A to memory cgroup B. Because the kernel stack of the thread hold a reference to the memory cgroup A. The thread can pin the memory cgroup A in the memory even if we remove the cgroup A. If we want to see this scenario by using the following script. We can see that the system has added 500 dying cgroups. #!/bin/bash cat /proc/cgroups | grep memory cd /sys/fs/cgroup/memory echo 1 > memory.move_charge_at_immigrate for i in range{1..500} do mkdir kmem_test echo $$ > kmem_test/cgroup.procs sleep 3600 & echo $$ > cgroup.procs echo `cat kmem_test/cgroup.procs` > cgroup.procs rmdir kmem_test done cat /proc/cgroups | grep memory This patchset aims to make those kmem pages drop the reference to memory cgroup by using the APIs of obj_cgroup. Finally, we can see that the number of the dying cgroups will not increase if we run the above test script. Patch 1-3 are using obj_cgroup APIs to charge kmem pages. The remote memory cgroup charing APIs is a mechanism to charge kernel memory to a given memory cgroup. So I also make it use the APIs of obj_cgroup. Patch 4-5 are doing this. Muchun Song (5): mm: memcontrol: introduce obj_cgroup_{un}charge_page mm: memcontrol: make page_memcg{_rcu} only applicable for non-kmem page mm: memcontrol: reparent the kmem pages on cgroup removal mm: memcontrol: move remote memcg charging APIs to CONFIG_MEMCG_KMEM mm: memcontrol: use object cgroup for remote memory cgroup charging fs/buffer.c | 10 +- fs/notify/fanotify/fanotify.c | 6 +- fs/notify/fanotify/fanotify_user.c | 2 +- fs/notify/group.c | 3 +- fs/notify/inotify/inotify_fsnotify.c | 8 +- fs/notify/inotify/inotify_user.c | 2 +- include/linux/bpf.h | 2 +- include/linux/fsnotify_backend.h | 2 +- include/linux/memcontrol.h | 109 +++++++++++--- include/linux/sched.h | 6 +- include/linux/sched/mm.h | 30 ++-- kernel/bpf/syscall.c | 35 ++--- kernel/fork.c | 4 +- mm/memcontrol.c | 276 ++++++++++++++++++++++------------- mm/page_alloc.c | 4 +- 15 files changed, 324 insertions(+), 175 deletions(-)