Re: [PATCH 7/8] mm: memcontrol: account "kmem" consumers in cgroup2 memory controller

Michal Hocko
2015-12-10T14:21:52Z

On Tue 08-12-15 13:34:24, Johannes Weiner wrote:
> The original cgroup memory controller has an extension to account slab
> memory (and other "kernel memory" consumers) in a separate "kmem"
> counter, once the user set an explicit limit on that "kmem" pool.
>
> However, this includes various consumers whose sizes are directly
> linked to userspace activity. Accounting them as an optional "kmem"
> extension is problematic for several reasons:
>
> 1. It leaves the main memory interface with incomplete semantics. A
> user who puts their workload into a cgroup and configures a memory
> limit does not expect us to leave holes in the containment as big
> as the dentry and inode cache, or the kernel stack pages.
>
> 2. If the limit set on this random historical subgroup of consumers is
> reached, subsequent allocations will fail even when the main memory
> pool available to the cgroup is not yet exhausted and/or has
> reclaimable memory in it.
>
> 3. Calling it 'kernel memory' is misleading. The dentry and inode
> caches are no more 'kernel' (or no less 'user') memory than the
> page cache itself. Treating these consumers as different classes is
> a historical implementation detail that should not leak to users.
>
> So, in addition to page cache, anonymous memory, and network socket
> memory, account the following memory consumers per default in the
> cgroup2 memory controller:
>
> - threadinfo
> - task_struct
> - task_delay_info
> - pid
> - cred
> - mm_struct
> - vm_area_struct and vm_region (nommu)
> - anon_vma and anon_vma_chain
> - signal_struct
> - sighand_struct
> - fs_struct
> - files_struct
> - fdtable and fdtable->full_fds_bits
> - dentry and external_name
> - inode for all filesystems.
>
> This should give us reasonable memory isolation for most common
> workloads out of the box.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> mm/memcontrol.c | 18 +++++++++++-------
> 1 file changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index ab72c47..d048137 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2356,13 +2356,14 @@ int __memcg_kmem_charge_memcg(struct page *page, gfp_t gfp, int order,
> if (!memcg_kmem_online(memcg))
> return 0;
>
> - if (!page_counter_try_charge(&memcg->kmem, nr_pages, &counter))
> - return -ENOMEM;
> -
> ret = try_charge(memcg, gfp, nr_pages);
> - if (ret) {
> - page_counter_uncharge(&memcg->kmem, nr_pages);
> + if (ret)
> return ret;
> +
> + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) &&
> + !page_counter_try_charge(&memcg->kmem, nr_pages, &counter)) {
> + cancel_charge(memcg, nr_pages);
> + return -ENOMEM;
> }
>
> page->mem_cgroup = memcg;
> @@ -2391,7 +2392,9 @@ void __memcg_kmem_uncharge(struct page *page, int order)
>
> VM_BUG_ON_PAGE(mem_cgroup_is_root(memcg), page);
>
> - page_counter_uncharge(&memcg->kmem, nr_pages);
> + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
> + page_counter_uncharge(&memcg->kmem, nr_pages);
> +
> page_counter_uncharge(&memcg->memory, nr_pages);
> if (do_memsw_account())
> page_counter_uncharge(&memcg->memsw, nr_pages);
> @@ -2895,7 +2898,8 @@ static int memcg_propagate_kmem(struct mem_cgroup *memcg)
> * onlined after this point, because it has at least one child
> * already.
> */
> - if (memcg_kmem_online(parent))
> + if (cgroup_subsys_on_dfl(memory_cgrp_subsys) ||
> + memcg_kmem_online(parent))
> ret = memcg_online_kmem(memcg);
> mutex_unlock(&memcg_limit_mutex);
> return ret;
> --
> 2.6.3

--
Michal Hocko
SUSE Labs