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Message-ID: <CALvZod6_iWt9v=0mmHoeZpBtCGhjuDo9OusoamFUTh2BxceXFg@mail.gmail.com>
Date: Tue, 9 Nov 2021 22:15:33 -0800
From: Shakeel Butt <shakeelb@...gle.com>
To: Mina Almasry <almasrymina@...gle.com>
Cc: Mike Kravetz <mike.kravetz@...cle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Shuah Khan <shuah@...nel.org>,
Miaohe Lin <linmiaohe@...wei.com>,
Oscar Salvador <osalvador@...e.de>,
Michal Hocko <mhocko@...e.com>,
Muchun Song <songmuchun@...edance.com>,
David Rientjes <rientjes@...gle.com>,
Jue Wang <juew@...gle.com>, Yang Yao <ygyao@...gle.com>,
Joanna Li <joannali@...gle.com>,
Cannon Matthews <cannonmatthews@...gle.com>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] hugetlb: Add hugetlb.*.numa_stat file
On Mon, Nov 8, 2021 at 1:05 PM Mina Almasry <almasrymina@...gle.com> wrote:
>
> For hugetlb backed jobs/VMs it's critical to understand the numa
> information for the memory backing these jobs to deliver optimal
> performance.
>
> Currently this technically can be queried from /proc/self/numa_maps, but
> there are significant issues with that. Namely:
> 1. Memory can be mapped on unmapped.
or*
> 2. numa_maps are per process and need to be aggregated across all
> processes in the cgroup. For shared memory this is more involved as
> the userspace needs to make sure it doesn't double count shared
> mappings.
> 3. I believe querying numa_maps needs to hold the mmap_lock which adds
> to the contention on this lock.
>
> For these reasons I propose simply adding hugetlb.*.numa_stat file,
> which shows the numa information of the cgroup similarly to
> memory.numa_stat.
>
> On cgroup-v2:
> cat /sys/fs/cgroup/unified/test/hugetlb.2MB.numa_stat
> total=2097152 N0=2097152 N1=0
>
> On cgroup-v1:
> cat /sys/fs/cgroup/hugetlb/test/hugetlb.2MB.numa_stat
> total=2097152 N0=2097152 N1=0
> hierarichal_total=2097152 N0=2097152 N1=0
>
> This patch was tested manually by allocating hugetlb memory and querying
> the hugetlb.*.numa_stat file of the cgroup and its parents.
> 
> Cc: Mike Kravetz <mike.kravetz@...cle.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Shuah Khan <shuah@...nel.org>
> Cc: Miaohe Lin <linmiaohe@...wei.com>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Muchun Song <songmuchun@...edance.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Shakeel Butt <shakeelb@...gle.com>
> Cc: Jue Wang <juew@...gle.com>
> Cc: Yang Yao <ygyao@...gle.com>
> Cc: Joanna Li <joannali@...gle.com>
> Cc: Cannon Matthews <cannonmatthews@...gle.com>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
>
> Signed-off-by: Mina Almasry <almasrymina@...gle.com>
>
[...]
> diff --git a/include/linux/hugetlb_cgroup.h b/include/linux/hugetlb_cgroup.h
> index c137396129db..54ff6ec68ed3 100644
> --- a/include/linux/hugetlb_cgroup.h
> +++ b/include/linux/hugetlb_cgroup.h
> @@ -36,6 +36,11 @@ enum hugetlb_memory_event {
> HUGETLB_NR_MEMORY_EVENTS,
> };
>
> +struct hugetlb_cgroup_per_node {
> + /* hugetlb usage in bytes over all hstates. */
> + unsigned long usage[HUGE_MAX_HSTATE];
Should we use atomic here? Is this safe for all archs?
[...]
>
> /*
> @@ -292,7 +321,8 @@ static void __hugetlb_cgroup_commit_charge(int idx, unsigned long nr_pages,
> return;
>
> __set_hugetlb_cgroup(page, h_cg, rsvd);
> - return;
> + if (!rsvd && h_cg)
No need to check h_cg.
> + h_cg->nodeinfo[page_to_nid(page)]->usage[idx] += nr_pages;
> }
>
> void hugetlb_cgroup_commit_charge(int idx, unsigned long nr_pages,
> @@ -331,7 +361,8 @@ static void __hugetlb_cgroup_uncharge_page(int idx, unsigned long nr_pages,
>
> if (rsvd)
> css_put(&h_cg->css);
> -
> + else
> + h_cg->nodeinfo[page_to_nid(page)]->usage[idx] -= nr_pages;
> return;
> }
>
> @@ -421,6 +452,58 @@ enum {
> RES_RSVD_FAILCNT,
> };
>
> +static int hugetlb_cgroup_read_numa_stat(struct seq_file *seq, void *dummy)
> +{
> + int nid;
> + struct cftype *cft = seq_cft(seq);
> + int idx = MEMFILE_IDX(cft->private);
> + bool legacy = MEMFILE_ATTR(cft->private);
> + struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(seq_css(seq));
> + struct cgroup_subsys_state *css;
> + unsigned long usage;
> +
> + if (legacy) {
> + /* Add up usage across all nodes for the non-hierarchical total. */
> + usage = 0;
> + for_each_node_state(nid, N_MEMORY)
> + usage += h_cg->nodeinfo[nid]->usage[idx];
> + seq_printf(seq, "total=%lu", usage * PAGE_SIZE);
> +
> + /* Simply print the per-node usage for the non-hierarchical total. */
> + for_each_node_state(nid, N_MEMORY)
> + seq_printf(seq, " N%d=%lu", nid,
> + h_cg->nodeinfo[nid]->usage[idx] * PAGE_SIZE);
> + seq_putc(seq, '\n');
> + }
> +
> + /*
> + * The hierarchical total is pretty much the value recorded by the
> + * counter, so use that.
> + */
> + seq_printf(seq, "%stotal=%lu", legacy ? "hierarichal_" : "",
> + page_counter_read(&h_cg->hugepage[idx]) * PAGE_SIZE);
> +
> + /*
> + * For each node, transverse the css tree to obtain the hierarichal
> + * node usage.
> + */
> + for_each_node_state(nid, N_MEMORY) {
> + usage = 0;
> + rcu_read_lock();
> + css_for_each_descendant_pre(css, &h_cg->css) {
This will be slow. Do you really want to traverse the hugetlb-cgroup
tree that many times? We had similar issues with memcg stats as well
but got resolved with rstat.
Though I feel like hugetlb-cgroup is not that worried about
performance. There is no batching in the charging and uncharging
codepaths.
> + usage += hugetlb_cgroup_from_css(css)
> + ->nodeinfo[nid]
> + ->usage[idx];
> + }
> + rcu_read_unlock();
> + seq_printf(seq, " N%d=%lu", nid, usage * PAGE_SIZE);
> + }
> +
> + seq_putc(seq, '\n');
> +
> + return 0;
> +}
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