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SubjectRe: [RFC] Shared page accounting for memory cgroup
On Tue, 29 Dec 2009 23:57:43 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> Hi, Everyone,
>
> I've been working on heuristics for shared page accounting for the
> memory cgroup. I've tested the patches by creating multiple cgroups
> and running programs that share memory and observed the output.
>
> Comments?

Hmm? Why we have to do this in the kernel ?

Thanks,
-Kame

>
>
> Add shared accounting to memcg
>
> From: Balbir Singh <balbir@linux.vnet.ibm.com>
>
> Currently there is no accurate way of estimating how many pages are
> shared in a memory cgroup. The accurate way of accounting shared memory
> is to
>
> 1. Either follow every page rmap and track number of users
> 2. Iterate through the pages and use _mapcount
>
> We take an intermediate approach (suggested by Kamezawa), we sum up
> the file and anon rss of the mm's belonging to the cgroup and then
> subtract the values of anon rss and file mapped. This should give
> us a good estimate of the pages being shared.
>
> The shared statistic is called memory.shared_usage_in_bytes and
> does not support hierarchical information, just the information
> for the current cgroup.
>
> Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
> ---
>
> Documentation/cgroups/memory.txt | 6 +++++
> mm/memcontrol.c | 43 ++++++++++++++++++++++++++++++++++++++
> 2 files changed, 49 insertions(+), 0 deletions(-)
>
>
> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
> index b871f25..c2c70c9 100644
> --- a/Documentation/cgroups/memory.txt
> +++ b/Documentation/cgroups/memory.txt
> @@ -341,6 +341,12 @@ Note:
> - a cgroup which uses hierarchy and it has child cgroup.
> - a cgroup which uses hierarchy and not the root of hierarchy.
>
> +5.4 shared_usage_in_bytes
> + This data lists the number of shared bytes. The data provided
> + provides an approximation based on the anon and file rss counts
> + of all the mm's belonging to the cgroup. The sum above is subtracted
> + from the count of rss and file mapped count maintained within the
> + memory cgroup statistics (see section 5.2).
>
> 6. Hierarchy support
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 488b644..8e296be 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3052,6 +3052,45 @@ static int mem_cgroup_swappiness_write(struct cgroup *cgrp, struct cftype *cft,
> return 0;
> }
>
> +static u64 mem_cgroup_shared_read(struct cgroup *cgrp, struct cftype *cft)
> +{
> + struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
> + struct cgroup_iter it;
> + struct task_struct *tsk;
> + u64 total_rss = 0, shared;
> + struct mm_struct *mm;
> + s64 val;
> +
> + cgroup_iter_start(cgrp, &it);
> + val = mem_cgroup_read_stat(&memcg->stat, MEM_CGROUP_STAT_RSS);
> + val += mem_cgroup_read_stat(&memcg->stat, MEM_CGROUP_STAT_FILE_MAPPED);
> + while ((tsk = cgroup_iter_next(cgrp, &it))) {
> + if (!thread_group_leader(tsk))
> + continue;
> + mm = tsk->mm;
> + /*
> + * We can't use get_task_mm(), since mmput() its counterpart
> + * can sleep. We know that mm can't become invalid since
> + * we hold the css_set_lock (see cgroup_iter_start()).
> + */
> + if (tsk->flags & PF_KTHREAD || !mm)
> + continue;
> + total_rss += get_mm_counter(mm, file_rss) +
> + get_mm_counter(mm, anon_rss);
> + }
> + cgroup_iter_end(cgrp, &it);
> +
> + /*
> + * We need to tolerate negative values due to the difference in
> + * time of calculating total_rss and val, but the shared value
> + * converges to the correct value quite soon depending on the changing
> + * memory usage of the workload running in the memory cgroup.
> + */
> + shared = total_rss - val;
> + shared = max_t(s64, 0, shared);
> + shared <<= PAGE_SHIFT;
> + return shared;
> +}
>
> static struct cftype mem_cgroup_files[] = {
> {
> @@ -3101,6 +3140,10 @@ static struct cftype mem_cgroup_files[] = {
> .read_u64 = mem_cgroup_swappiness_read,
> .write_u64 = mem_cgroup_swappiness_write,
> },
> + {
> + .name = "shared_usage_in_bytes",
> + .read_u64 = mem_cgroup_shared_read,
> + },
> };
>
> #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
>
> --
> Balbir
>



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