Re: [PATCH] mm, memcg: cg2 memory{.swap,}.peak write handlers

[David Finkel <davidf@vimeo.com>]

Note: this is a simple rebase of a patch I sent a few months ago,
which received two acks before the thread petered out:
https://www.spinics.net/lists/cgroups/msg40602.html

Thanks,

On Mon, Jul 15, 2024 at 4:38 PM David Finkel <davidf@vimeo.com> wrote:
>
> Other mechanisms for querying the peak memory usage of either a process
> or v1 memory cgroup allow for resetting the high watermark. Restore
> parity with those mechanisms.
>
> For example:
>  - Any write to memory.max_usage_in_bytes in a cgroup v1 mount resets
>    the high watermark.
>  - writing "5" to the clear_refs pseudo-file in a processes's proc
>    directory resets the peak RSS.
>
> This change copies the cgroup v1 behavior so any write to the
> memory.peak and memory.swap.peak pseudo-files reset the high watermark
> to the current usage.
>
> This behavior is particularly useful for work scheduling systems that
> need to track memory usage of worker processes/cgroups per-work-item.
> Since memory can't be squeezed like CPU can (the OOM-killer has
> opinions), these systems need to track the peak memory usage to compute
> system/container fullness when binpacking workitems.
>
> Signed-off-by: David Finkel <davidf@vimeo.com>
> ---
>  Documentation/admin-guide/cgroup-v2.rst       | 20 +++---
>  mm/memcontrol.c                               | 23 ++++++
>  .../selftests/cgroup/test_memcontrol.c        | 72 ++++++++++++++++---
>  3 files changed, 99 insertions(+), 16 deletions(-)
>
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 8fbb0519d556..201d8e5d9f82 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1322,11 +1322,13 @@ PAGE_SIZE multiple when read back.
>         reclaim induced by memory.reclaim.
>
>    memory.peak
> -       A read-only single value file which exists on non-root
> -       cgroups.
> +       A read-write single value file which exists on non-root cgroups.
> +
> +       The max memory usage recorded for the cgroup and its descendants since
> +       either the creation of the cgroup or the most recent reset.
>
> -       The max memory usage recorded for the cgroup and its
> -       descendants since the creation of the cgroup.
> +       Any non-empty write to this file resets it to the current memory usage.
> +       All content written is completely ignored.
>
>    memory.oom.group
>         A read-write single value file which exists on non-root
> @@ -1652,11 +1654,13 @@ PAGE_SIZE multiple when read back.
>         Healthy workloads are not expected to reach this limit.
>
>    memory.swap.peak
> -       A read-only single value file which exists on non-root
> -       cgroups.
> +       A read-write single value file which exists on non-root cgroups.
> +
> +       The max swap usage recorded for the cgroup and its descendants since
> +       the creation of the cgroup or the most recent reset.
>
> -       The max swap usage recorded for the cgroup and its
> -       descendants since the creation of the cgroup.
> +       Any non-empty write to this file resets it to the current swap usage.
> +       All content written is completely ignored.
>
>    memory.swap.max
>         A read-write single value file which exists on non-root
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 8f2f1bb18c9c..abfa547615d6 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -25,6 +25,7 @@
>   * Copyright (C) 2020 Alibaba, Inc, Alex Shi
>   */
>
> +#include <linux/cgroup-defs.h>
>  #include <linux/page_counter.h>
>  #include <linux/memcontrol.h>
>  #include <linux/cgroup.h>
> @@ -6915,6 +6916,16 @@ static u64 memory_peak_read(struct cgroup_subsys_state *css,
>         return (u64)memcg->memory.watermark * PAGE_SIZE;
>  }
>
> +static ssize_t memory_peak_write(struct kernfs_open_file *of,
> +                                char *buf, size_t nbytes, loff_t off)
> +{
> +       struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
> +
> +       page_counter_reset_watermark(&memcg->memory);
> +
> +       return nbytes;
> +}
> +
>  static int memory_min_show(struct seq_file *m, void *v)
>  {
>         return seq_puts_memcg_tunable(m,
> @@ -7232,6 +7243,7 @@ static struct cftype memory_files[] = {
>                 .name = "peak",
>                 .flags = CFTYPE_NOT_ON_ROOT,
>                 .read_u64 = memory_peak_read,
> +               .write = memory_peak_write,
>         },
>         {
>                 .name = "min",
> @@ -8201,6 +8213,16 @@ static u64 swap_peak_read(struct cgroup_subsys_state *css,
>         return (u64)memcg->swap.watermark * PAGE_SIZE;
>  }
>
> +static ssize_t swap_peak_write(struct kernfs_open_file *of,
> +                                char *buf, size_t nbytes, loff_t off)
> +{
> +       struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
> +
> +       page_counter_reset_watermark(&memcg->swap);
> +
> +       return nbytes;
> +}
> +
>  static int swap_high_show(struct seq_file *m, void *v)
>  {
>         return seq_puts_memcg_tunable(m,
> @@ -8283,6 +8305,7 @@ static struct cftype swap_files[] = {
>                 .name = "swap.peak",
>                 .flags = CFTYPE_NOT_ON_ROOT,
>                 .read_u64 = swap_peak_read,
> +               .write = swap_peak_write,
>         },
>         {
>                 .name = "swap.events",
> diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
> index 41ae8047b889..681972de673b 100644
> --- a/tools/testing/selftests/cgroup/test_memcontrol.c
> +++ b/tools/testing/selftests/cgroup/test_memcontrol.c
> @@ -161,12 +161,12 @@ static int alloc_pagecache_50M_check(const char *cgroup, void *arg)
>  /*
>   * This test create a memory cgroup, allocates
>   * some anonymous memory and some pagecache
> - * and check memory.current and some memory.stat values.
> + * and checks memory.current, memory.peak, and some memory.stat values.
>   */
> -static int test_memcg_current(const char *root)
> +static int test_memcg_current_peak(const char *root)
>  {
>         int ret = KSFT_FAIL;
> -       long current;
> +       long current, peak, peak_reset;
>         char *memcg;
>
>         memcg = cg_name(root, "memcg_test");
> @@ -180,12 +180,32 @@ static int test_memcg_current(const char *root)
>         if (current != 0)
>                 goto cleanup;
>
> +       peak = cg_read_long(memcg, "memory.peak");
> +       if (peak != 0)
> +               goto cleanup;
> +
>         if (cg_run(memcg, alloc_anon_50M_check, NULL))
>                 goto cleanup;
>
> +       peak = cg_read_long(memcg, "memory.peak");
> +       if (peak < MB(50))
> +               goto cleanup;
> +
> +       peak_reset = cg_write(memcg, "memory.peak", "\n");
> +       if (peak_reset != 0)
> +               goto cleanup;
> +
> +       peak = cg_read_long(memcg, "memory.peak");
> +       if (peak > MB(30))
> +               goto cleanup;
> +
>         if (cg_run(memcg, alloc_pagecache_50M_check, NULL))
>                 goto cleanup;
>
> +       peak = cg_read_long(memcg, "memory.peak");
> +       if (peak < MB(50))
> +               goto cleanup;
> +
>         ret = KSFT_PASS;
>
>  cleanup:
> @@ -817,13 +837,14 @@ static int alloc_anon_50M_check_swap(const char *cgroup, void *arg)
>
>  /*
>   * This test checks that memory.swap.max limits the amount of
> - * anonymous memory which can be swapped out.
> + * anonymous memory which can be swapped out. Additionally, it verifies that
> + * memory.swap.peak reflects the high watermark and can be reset.
>   */
> -static int test_memcg_swap_max(const char *root)
> +static int test_memcg_swap_max_peak(const char *root)
>  {
>         int ret = KSFT_FAIL;
>         char *memcg;
> -       long max;
> +       long max, peak;
>
>         if (!is_swap_enabled())
>                 return KSFT_SKIP;
> @@ -840,6 +861,12 @@ static int test_memcg_swap_max(const char *root)
>                 goto cleanup;
>         }
>
> +       if (cg_read_long(memcg, "memory.swap.peak"))
> +               goto cleanup;
> +
> +       if (cg_read_long(memcg, "memory.peak"))
> +               goto cleanup;
> +
>         if (cg_read_strcmp(memcg, "memory.max", "max\n"))
>                 goto cleanup;
>
> @@ -862,6 +889,27 @@ static int test_memcg_swap_max(const char *root)
>         if (cg_read_key_long(memcg, "memory.events", "oom_kill ") != 1)
>                 goto cleanup;
>
> +       peak = cg_read_long(memcg, "memory.peak");
> +       if (peak < MB(29))
> +               goto cleanup;
> +
> +       peak = cg_read_long(memcg, "memory.swap.peak");
> +       if (peak < MB(29))
> +               goto cleanup;
> +
> +       if (cg_write(memcg, "memory.swap.peak", "\n"))
> +               goto cleanup;
> +
> +       if (cg_read_long(memcg, "memory.swap.peak") > MB(10))
> +               goto cleanup;
> +
> +
> +       if (cg_write(memcg, "memory.peak", "\n"))
> +               goto cleanup;
> +
> +       if (cg_read_long(memcg, "memory.peak"))
> +               goto cleanup;
> +
>         if (cg_run(memcg, alloc_anon_50M_check_swap, (void *)MB(30)))
>                 goto cleanup;
>
> @@ -869,6 +917,14 @@ static int test_memcg_swap_max(const char *root)
>         if (max <= 0)
>                 goto cleanup;
>
> +       peak = cg_read_long(memcg, "memory.peak");
> +       if (peak < MB(29))
> +               goto cleanup;
> +
> +       peak = cg_read_long(memcg, "memory.swap.peak");
> +       if (peak < MB(19))
> +               goto cleanup;
> +
>         ret = KSFT_PASS;
>
>  cleanup:
> @@ -1295,7 +1351,7 @@ struct memcg_test {
>         const char *name;
>  } tests[] = {
>         T(test_memcg_subtree_control),
> -       T(test_memcg_current),
> +       T(test_memcg_current_peak),
>         T(test_memcg_min),
>         T(test_memcg_low),
>         T(test_memcg_high),
> @@ -1303,7 +1359,7 @@ struct memcg_test {
>         T(test_memcg_max),
>         T(test_memcg_reclaim),
>         T(test_memcg_oom_events),
> -       T(test_memcg_swap_max),
> +       T(test_memcg_swap_max_peak),
>         T(test_memcg_sock),
>         T(test_memcg_oom_group_leaf_events),
>         T(test_memcg_oom_group_parent_events),
> --
> 2.40.1
>


-- 
David Finkel
Senior Principal Software Engineer, Core Services