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Date: Wed, 6 Jan 2010 09:07:08 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: balbir@...ux.vnet.ibm.com
Cc: Andrew Morton <akpm@...ux-foundation.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -mm] Shared Page accounting for memory cgroup (v2)
On Wed, 6 Jan 2010 00:22:26 +0530
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
> Hi, All,
>
> No major changes from v1, except for the use of get_mm_rss().
> Kamezawa-San felt that this can be done in user space and I responded
> to him with my concerns of doing it in user space. The thread
> can be found at http://thread.gmane.org/gmane.linux.kernel.mm/42367.
>
> If there are no major objections, can I ask for a merge into -mm.
> Andrew, the patches are against mmotm 10 December 2009, if there
> are some merge conflicts, please let me know, I can rebase after
> you release the next mmotm.
>
The problem is that this isn't "shared" uasge but "considered to be shared"
usage. Okay ?
Then I don't want to provide this misleading value as "official report" from
the kernel. And this can be done in userland.
Then, NACK.
Thanks,
-Kame
>
> Add shared accounting to memcg
>
> From: Balbir Singh <balbir@...ux.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@...ux.vnet.ibm.com>
> ---
>
> Documentation/cgroups/memory.txt | 6 +++++
> mm/memcontrol.c | 42 ++++++++++++++++++++++++++++++++++++++
> 2 files changed, 48 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..e49b47a 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3052,6 +3052,44 @@ 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_rss(mm);
> + }
> + 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 +3139,10 @@ 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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