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

[Michal Hocko <mhocko@suse.com>]

On Mon 04-12-23 14:41:56, David Finkel 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.

I do not understand the OOM-killer reference here but I do understand
that your worker reuses a cgroup and you want a peak memory consumption
of a single run to better profile/configure the memcg configuration for
the specific worker type. Correct?

> Signed-off-by: David Finkel <davidf@vimeo.com>

Makes sense to me
Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
>  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 3f85254f3cef..95af0628dc44 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1305,11 +1305,13 @@ 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
> @@ -1626,11 +1628,13 @@ 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 1c1061df9cd1..b04af158922d 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>
> @@ -6635,6 +6636,16 @@ 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,
> @@ -6947,6 +6958,7 @@ static struct cftype memory_files[] = {
>  		.name = "peak",
>  		.flags = CFTYPE_NOT_ON_ROOT,
>  		.read_u64 = memory_peak_read,
> +		.write = memory_peak_write,
>  	},
>  	{
>  		.name = "min",
> @@ -7917,6 +7929,16 @@ 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,
> @@ -7999,6 +8021,7 @@ 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 c7c9572003a8..0326c317f1f2 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:
> @@ -815,13 +835,14 @@ 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;
> @@ -838,6 +859,12 @@ 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;
>  
> @@ -860,6 +887,27 @@ 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;
>  
> @@ -867,6 +915,14 @@ 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:
> @@ -1293,7 +1349,7 @@ 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),
> @@ -1301,7 +1357,7 @@ 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),
> -- 
> 2.39.2

-- 
Michal Hocko
SUSE Labs