memcg: release kmemcg_id on css offline

Hi,

There's one thing about kmemcg implementation that's bothering me. It's about arrays holding per-memcg data (e.g. kmem_cache->memcg_params-> memcg_caches). On kmalloc or list_lru_{add,del} we want to quickly lookup the copy of kmem_cache or list_lru corresponding to the current cgroup. Currently, we hold all per-memcg caches/lists in an array indexed by mem_cgroup->kmemcg_id. This allows us to lookup quickly, and that's nice, but the arrays can grow indefinitely, because we reserve slots for all cgroups, including offlined, and this is disastrous and must be fixed.

There are several ways to fix this issue [1], but it seems the best we can do is to free kmemcg_id on css offline (solution #2). The idea is that we actually only need kmemcg_id on kmem cache allocations, in order to lookup the kmem cache copy corresponding to the allocating memory cgroup, while it is never used of kmem frees. We do rely on kmemcg_id being unique for each cgroup in some places, but they are easy to fix. And regarding per memcg list_lru, which are indexed by kmemcg_id, we can easily reparent them - it is as simple as splicing lists. This patch set therefore implements this approach.

It is organized as follows:
- Currently, sl[AU]b core relies on kmemcg_id being unique per kmem_cache. Patches 1-4 fix that.
- Patch 5 makes memcg_cache_params->memcg_caches entries released on css offline.
- Patch 6 alters the list_lru API a bit to facilitate reparenting.
- Patch 7 implements per memcg list_lru reparenting on css offline. After list_lrus have been reparented, there's no need to keep kmemcg_id any more, so we can free it on css offline.

Changes in v2:
- rebase on top of v3.19-rc4-mmotm-2015-01-16-15-50
- release css->id after css_free to avoid kmem cache name clashes

v1: https://lkml.org/lkml/2015/1/16/285

[1] https://lkml.org/lkml/2015/1/13/107

Thanks,

Vladimir Davydov (7):
slab: embed memcg_cache_params to kmem_cache
slab: link memcg caches of the same kind into a list
cgroup: release css->id after css_free
slab: use css id for naming per memcg caches
memcg: free memcg_caches slot on css offline
list_lru: add helpers to isolate items
memcg: reparent list_lrus and free kmemcg_id on css offline

 fs/dcache.c              |   21 +++---
 fs/gfs2/quota.c          |    5 +-
 fs/inode.c               |    8 +--
 fs/xfs/xfs_buf.c         |    6 +-
 fs/xfs/xfs_qm.c          |    5 +-
 include/linux/list_lru.h |   12 +++-
 include/linux/slab.h     |   31 +++++----
 include/linux/slab_def.h |    2 +-
 include/linux/slub_def.h |    2 +-
 kernel/cgroup.c          |   10 ++-
 mm/list_lru.c            |   65 ++++++++++++++++--
 mm/memcontrol.c          |   86 ++++++++++++++++++-----
 mm/slab.c                |   13 ++--
 mm/slab.h                |   65 +++++++++++-------
 mm/slab_common.c         |  172 +++++++++++++++++++++++++++-------------------
 mm/slub.c                |   24 +++----
 mm/workingset.c          |    3 +-
 17 files changed, 343 insertions(+), 187 deletions(-)

1.7.10.4

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