Date:   Sun, 7 Nov 2021 15:09:31 -0800
From:   Mina Almasry <almasrymina@...gle.com>
To:     Muchun Song <songmuchun@...edance.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>,
        David Rientjes <rientjes@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>, Jue Wang <juew@...gle.com>,
        Yang Yao <ygyao@...gle.com>, Joanna Li <joannali@...gle.com>,
        Cannon Matthews <cannonmatthews@...gle.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] hugetlb: Add hugetlb.*.numa_stat file

On Fri, Nov 5, 2021 at 11:55 PM Muchun Song <songmuchun@...edance.com> wrote:
>
> On Thu, Nov 4, 2021 at 12:53 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.
> > 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>
> >
> > ---
> >
> > Changes in v3:
> > - Fixed typos (sorry!)
> > - Used conventional locations for cgroups mount points in docs/commit
> > message.
> > - Updated docs.
> > - Handle kzalloc_node failure, and proper deallocation of per node data.
> > - Use struct_size() to calculate the struct size.
> > - Use nr_node_ids instead of MAX_NUMNODES.
> > - Updated comments per multi-line comment pattern.
> >
> > Changes in v2:
> > - Fix warning Reported-by: kernel test robot <lkp@...el.com>
> > ---
> >  .../admin-guide/cgroup-v1/hugetlb.rst         |   4 +
> >  Documentation/admin-guide/cgroup-v2.rst       |   5 +
> >  include/linux/hugetlb.h                       |   4 +-
> >  include/linux/hugetlb_cgroup.h                |   7 ++
> >  mm/hugetlb_cgroup.c                           | 116 ++++++++++++++++--
> >  .../testing/selftests/vm/write_to_hugetlbfs.c |   9 +-
> >  6 files changed, 132 insertions(+), 13 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/cgroup-v1/hugetlb.rst b/Documentation/admin-guide/cgroup-v1/hugetlb.rst
> > index 338f2c7d7a1c..0fa724d82abb 100644
> > --- a/Documentation/admin-guide/cgroup-v1/hugetlb.rst
> > +++ b/Documentation/admin-guide/cgroup-v1/hugetlb.rst
> > @@ -29,12 +29,14 @@ Brief summary of control files::
> >   hugetlb.<hugepagesize>.max_usage_in_bytes             # show max "hugepagesize" hugetlb  usage recorded
> >   hugetlb.<hugepagesize>.usage_in_bytes                 # show current usage for "hugepagesize" hugetlb
> >   hugetlb.<hugepagesize>.failcnt                        # show the number of allocation failure due to HugeTLB usage limit
> > + hugetlb.<hugepagesize>.numa_stat                      # show the numa information of the hugetlb memory charged to this cgroup
> >
> >  For a system supporting three hugepage sizes (64k, 32M and 1G), the control
> >  files include::
> >
> >    hugetlb.1GB.limit_in_bytes
> >    hugetlb.1GB.max_usage_in_bytes
> > +  hugetlb.1GB.numa_stat
> >    hugetlb.1GB.usage_in_bytes
> >    hugetlb.1GB.failcnt
> >    hugetlb.1GB.rsvd.limit_in_bytes
> > @@ -43,6 +45,7 @@ files include::
> >    hugetlb.1GB.rsvd.failcnt
> >    hugetlb.64KB.limit_in_bytes
> >    hugetlb.64KB.max_usage_in_bytes
> > +  hugetlb.64KB.numa_stat
> >    hugetlb.64KB.usage_in_bytes
> >    hugetlb.64KB.failcnt
> >    hugetlb.64KB.rsvd.limit_in_bytes
> > @@ -51,6 +54,7 @@ files include::
> >    hugetlb.64KB.rsvd.failcnt
> >    hugetlb.32MB.limit_in_bytes
> >    hugetlb.32MB.max_usage_in_bytes
> > +  hugetlb.32MB.numa_stat
> >    hugetlb.32MB.usage_in_bytes
> >    hugetlb.32MB.failcnt
> >    hugetlb.32MB.rsvd.limit_in_bytes
> > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> > index 4d8c27eca96b..356847f8f008 100644
> > --- a/Documentation/admin-guide/cgroup-v2.rst
> > +++ b/Documentation/admin-guide/cgroup-v2.rst
> > @@ -2252,6 +2252,11 @@ HugeTLB Interface Files
> >         are local to the cgroup i.e. not hierarchical. The file modified event
> >         generated on this file reflects only the local events.
> >
> > +  hugetlb.<hugepagesize>.numa_stat
> > +       Similar to memory.numa_stat, it shows the numa information of the
> > +        hugetlb pages of <hugepagesize> in this cgroup.  Only active in
> > +        use hugetlb pages are included.  The per-node values are in bytes.
> > +
> >  Misc
> >  ----
> >
> > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> > index 1faebe1cd0ed..0445faaa636e 100644
> > --- a/include/linux/hugetlb.h
> > +++ b/include/linux/hugetlb.h
> > @@ -613,8 +613,8 @@ struct hstate {
> >  #endif
> >  #ifdef CONFIG_CGROUP_HUGETLB
> >         /* cgroup control files */
> > -       struct cftype cgroup_files_dfl[7];
> > -       struct cftype cgroup_files_legacy[9];
> > +       struct cftype cgroup_files_dfl[8];
> > +       struct cftype cgroup_files_legacy[10];
> >  #endif
> >         char name[HSTATE_NAME_LEN];
> >  };
> > 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];
> > +};
> > +
> >  struct hugetlb_cgroup {
> >         struct cgroup_subsys_state css;
> >
> > @@ -57,6 +62,8 @@ struct hugetlb_cgroup {
> >
> >         /* Handle for "hugetlb.events.local" */
> >         struct cgroup_file events_local_file[HUGE_MAX_HSTATE];
> > +
> > +       struct hugetlb_cgroup_per_node *nodeinfo[];
> >  };
> >
> >  static inline struct hugetlb_cgroup *
> > diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
> > index 5383023d0cca..6be6dfb4f7a7 100644
> > --- a/mm/hugetlb_cgroup.c
> > +++ b/mm/hugetlb_cgroup.c
> > @@ -126,29 +126,59 @@ static void hugetlb_cgroup_init(struct hugetlb_cgroup *h_cgroup,
> >         }
> >  }
> >
> > +static void hugetlb_cgroup_free(struct hugetlb_cgroup *h_cgroup)
> > +{
> > +       int node;
> > +
> > +       for_each_node(node) {
> > +               kfree(h_cgroup->nodeinfo[node]);
> > +       }
>
> Braces {} are not necessary for single statement blocks.
>

Will be removed in v4.

> > +       kfree(h_cgroup);
> > +}
> > +
> >  static struct cgroup_subsys_state *
> >  hugetlb_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
> >  {
> >         struct hugetlb_cgroup *parent_h_cgroup = hugetlb_cgroup_from_css(parent_css);
> >         struct hugetlb_cgroup *h_cgroup;
> > +       int node;
> > +
> > +       h_cgroup = kzalloc(struct_size(h_cgroup, nodeinfo, nr_node_ids),
> > +                          GFP_KERNEL);
> >
> > -       h_cgroup = kzalloc(sizeof(*h_cgroup), GFP_KERNEL);
> >         if (!h_cgroup)
> >                 return ERR_PTR(-ENOMEM);
> >
> >         if (!parent_h_cgroup)
> >                 root_h_cgroup = h_cgroup;
> >
> > +       /*
> > +        * TODO: this routine can waste much memory for nodes which will
> > +        * never be onlined. It's better to use memory hotplug callback
> > +        * function.
> > +        */
> > +       for_each_node(node) {
> > +               /* Set node_to_alloc to -1 for offline nodes. */
> > +               int node_to_alloc =
> > +                       node_state(node, N_NORMAL_MEMORY) ? node : -1;
> > +               h_cgroup->nodeinfo[node] =
> > +                       kzalloc_node(sizeof(struct hugetlb_cgroup_per_node),
> > +                                    GFP_KERNEL, node_to_alloc);
> > +               if (!h_cgroup->nodeinfo[node])
> > +                       goto fail_alloc_nodeinfo;
> > +       }
> > +
> >         hugetlb_cgroup_init(h_cgroup, parent_h_cgroup);
> >         return &h_cgroup->css;
> > +
> > +fail_alloc_nodeinfo:
> > +       hugetlb_cgroup_free(h_cgroup);
> > +       return ERR_PTR(-ENOMEM);
> >  }
> >
> >  static void hugetlb_cgroup_css_free(struct cgroup_subsys_state *css)
> >  {
> > -       struct hugetlb_cgroup *h_cgroup;
> > -
> > -       h_cgroup = hugetlb_cgroup_from_css(css);
> > -       kfree(h_cgroup);
> > +       hugetlb_cgroup_free(hugetlb_cgroup_from_css(css));
> >  }
> >
> >  /*
> > @@ -292,7 +322,9 @@ 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)
> > +               h_cg->nodeinfo[page_to_nid(page)]->usage[idx] += nr_pages
> > +                                                                << PAGE_SHIFT;
>
> How about changing the unit from byte to page? In this case, we
> do not need to do shift operations here. When the user reads
> numa_stat, then converting the pages to bytes for them.
>

So all the other hugetlb_cgroup interfaces (max, current,
usage_in_bytes, limit_in_bytes), are in bytes and not pages, and
memory.numa_stat is also in bytes. I think providing consistency here
is a really good thing.

> >  }
> >
> >  void hugetlb_cgroup_commit_charge(int idx, unsigned long nr_pages,
> > @@ -331,7 +363,9 @@ 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
> > +                                                                << PAGE_SHIFT;
> >         return;
> >  }
> >
> > @@ -421,6 +455,58 @@ 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);
> > +
> > +               /* 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]);
> > +               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) {
> > +                       usage += hugetlb_cgroup_from_css(css)
> > +                                        ->nodeinfo[nid]
> > +                                        ->usage[idx];
> > +               }
> > +               rcu_read_unlock();
> > +               seq_printf(seq, " N%d=%lu", nid, usage);
> > +       }
> > +
> > +       seq_putc(seq, '\n');
> > +
> > +       return 0;
> > +}
> > +
> >  static u64 hugetlb_cgroup_read_u64(struct cgroup_subsys_state *css,
> >                                    struct cftype *cft)
> >  {
> > @@ -671,8 +757,14 @@ static void __init __hugetlb_cgroup_file_dfl_init(int idx)
> >                                     events_local_file[idx]);
> >         cft->flags = CFTYPE_NOT_ON_ROOT;
> >
> > -       /* NULL terminate the last cft */
> > +       /* Add the numa stat file */
> >         cft = &h->cgroup_files_dfl[6];
> > +       snprintf(cft->name, MAX_CFTYPE_NAME, "%s.numa_stat", buf);
> > +       cft->seq_show = hugetlb_cgroup_read_numa_stat;
> > +       cft->flags = CFTYPE_NOT_ON_ROOT;
> > +
> > +       /* NULL terminate the last cft */
> > +       cft = &h->cgroup_files_dfl[7];
> >         memset(cft, 0, sizeof(*cft));
> >
> >         WARN_ON(cgroup_add_dfl_cftypes(&hugetlb_cgrp_subsys,
> > @@ -742,8 +834,14 @@ static void __init __hugetlb_cgroup_file_legacy_init(int idx)
> >         cft->write = hugetlb_cgroup_reset;
> >         cft->read_u64 = hugetlb_cgroup_read_u64;
> >
> > +       /* Add the numa stat file */
> > +       cft = &h->cgroup_files_dfl[8];
> > +       snprintf(cft->name, MAX_CFTYPE_NAME, "%s.numa_stat", buf);
> > +       cft->private = MEMFILE_PRIVATE(idx, 1);
> > +       cft->seq_show = hugetlb_cgroup_read_numa_stat;
> > +
> >         /* NULL terminate the last cft */
> > -       cft = &h->cgroup_files_legacy[8];
> > +       cft = &h->cgroup_files_legacy[9];
> >         memset(cft, 0, sizeof(*cft));
> >
> >         WARN_ON(cgroup_add_legacy_cftypes(&hugetlb_cgrp_subsys,
> > diff --git a/tools/testing/selftests/vm/write_to_hugetlbfs.c b/tools/testing/selftests/vm/write_to_hugetlbfs.c
> > index 6a2caba19ee1..d2da6315a40c 100644
> > --- a/tools/testing/selftests/vm/write_to_hugetlbfs.c
> > +++ b/tools/testing/selftests/vm/write_to_hugetlbfs.c
> > @@ -37,8 +37,8 @@ static int shmid;
> >  static void exit_usage(void)
> >  {
> >         printf("Usage: %s -p <path to hugetlbfs file> -s <size to map> "
> > -              "[-m <0=hugetlbfs | 1=mmap(MAP_HUGETLB)>] [-l] [-r] "
> > -              "[-o] [-w] [-n]\n",
> > +              "[-m <0=hugetlbfs | 1=mmap(MAP_HUGETLB)>] [-l(sleep)] [-r(private)] "
> > +              "[-o(populate)] [-w(rite)] [-n(o-reserve)]\n",
>
> Why do those changes? It seems like it does not belong
> to this patch. Please explain why you did this in changelog
> and separate those lines into another patch.
>
> Thanks.
>

So I used writo_to_hugetlbfs to test this patch, and I forgot what the
flags do so I clarified them, but sure yes these changes aren't
related to numa_stat. I'll drop them from v4 and I can always upload
them later.

> >                self);
> >         exit(EXIT_FAILURE);
> >  }
> > @@ -161,6 +161,11 @@ int main(int argc, char **argv)
> >         else
> >                 printf("RESERVE mapping.\n");
> >
> > +       if (want_sleep)
> > +               printf("Sleeping\n");
> > +       else
> > +               printf("Not sleeping\n");
> > +
> >         switch (method) {
> >         case HUGETLBFS:
> >                 printf("Allocating using HUGETLBFS.\n");
> > --
> > 2.33.1.1089.g2158813163f-goog

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