On Mon, Jul 22, 2024 at 11:17:13AM -0400, 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, but with a less racy API.
>
> 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 is an evolution of a previous patch, which mostly copied the
> cgroup v1 behavior, however, there were concerns about races/ownership
> issues with a global reset, so instead this change makes the reset
> filedescriptor-local.
>
> Writing a specific string to the memory.peak and memory.swap.peak
> pseudo-files reset the high watermark to the current usage for
> subsequent reads through that same fd.
>
> Notably, following Johannes's suggestion, this implementation moves the
> O(fds that have written) behavior onto the fd write(2) path. Instead, on
> the page-allocation path, we simply add one additional watermark to
> conditionally bump per-hierarchy level in the page-counter.
>
> 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.
>
> Most notably, Vimeo's use-case involves a system that's doing global
> binpacking across many Kubernetes pods/containers, and while we can use
> PSI for some local decisions about overload, we strive to avoid packing
> workloads too tightly in the first place. To facilitate this, we track
> the peak memory usage. However, since we run with long-lived workers (to
> amortize startup costs) we need a way to track the high watermark while
> a work-item is executing. Polling runs the risk of missing short spikes
> that last for timescales below the polling interval, and peak memory
> tracking at the cgroup level is otherwise perfect for this use-case.
>
> As this data is used to ensure that binpacked work ends up with
> sufficient headroom, this use-case mostly avoids the inaccuracies
> surrounding reclaimable memory.
>
> Suggested-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Signed-off-by: David Finkel <davidf@xxxxxxxxx>
> ---
> Documentation/admin-guide/cgroup-v2.rst | 26 +-
> include/linux/cgroup.h | 7 +
> include/linux/memcontrol.h | 5 +
> include/linux/page_counter.h | 6 +
> kernel/cgroup/cgroup-internal.h | 2 +
> kernel/cgroup/cgroup.c | 7 +
> mm/memcontrol.c | 165 ++++++++++++-
> mm/page_counter.c | 4 +
> tools/testing/selftests/cgroup/cgroup_util.c | 22 ++
> tools/testing/selftests/cgroup/cgroup_util.h | 2 +
> .../selftests/cgroup/test_memcontrol.c | 227 +++++++++++++++++-
> 11 files changed, 448 insertions(+), 25 deletions(-)
>
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 8fbb0519d556..10a2f919128f 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1322,11 +1322,16 @@ 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 for that fd.
>
> - The max memory usage recorded for the cgroup and its
> - descendants since the creation of the cgroup.
> + A write of the string "fd_local_reset" to this file resets it to the
> + current memory usage for subsequent reads through the same
Hi David!
Not a very strong preference, but with the current design, do we really expect
to have a non-local reset? If not, can we agree on a "reset" string instead
for a sake of simplicity?
> + file descriptor.
> + Attempts to write any other string will return EINVAL
> + (modulo leading and trailing whitespace).
>
> memory.oom.group
> A read-write single value file which exists on non-root
> @@ -1652,11 +1657,16 @@ 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 for that fd.
>
> - The max swap usage recorded for the cgroup and its
> - descendants since the creation of the cgroup.
> + A write of the string "fd_local_reset" to this file resets it to the
> + current memory usage for subsequent reads through the same
> + file descriptor.
> + Attempts to write any other string will return EINVAL
> + (modulo leading and trailing whitespace).
>
> memory.swap.max
> A read-write single value file which exists on non-root
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index 2150ca60394b..9bda441227ea 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -855,4 +855,11 @@ static inline void cgroup_bpf_put(struct cgroup *cgrp) {}
>
> struct cgroup *task_get_cgroup1(struct task_struct *tsk, int hierarchy_id);
>
> +struct memcg_peak_mem_ctx {
> + long local_watermark;
> + struct memcg_peak_mem_ctx *next, *prev;
Please, take a look at include/linux/list.h and use it instead of
re-implementing list operations from scratch.
> +};
> +
> +struct memcg_peak_mem_ctx *memcg_extract_peak_mem_ctx(struct kernfs_open_file *of);
> +
> #endif /* _LINUX_CGROUP_H */
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 030d34e9d117..6be7507c6fd3 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -198,6 +198,11 @@ struct mem_cgroup {
> struct page_counter kmem; /* v1 only */
> struct page_counter tcpmem; /* v1 only */
>
> + /* lists of memcg peak watching contexts on swap and memory */
> + struct memcg_peak_mem_ctx *peak_memory_local_watermark_watchers;
> + struct memcg_peak_mem_ctx *peak_swap_local_watermark_watchers;
> + spinlock_t pagecounter_peak_watchers_lock;
> +
> /* Range enforcement for interrupt charges */
> struct work_struct high_work;
>
> diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h
> index 8cd858d912c4..047ceaece258 100644
> --- a/include/linux/page_counter.h
> +++ b/include/linux/page_counter.h
> @@ -26,6 +26,7 @@ struct page_counter {
> atomic_long_t children_low_usage;
>
> unsigned long watermark;
> + unsigned long local_watermark; /* track min of fd-local resets */
> unsigned long failcnt;
>
> /* Keep all the read most fields in a separete cacheline. */
> @@ -81,4 +82,9 @@ static inline void page_counter_reset_watermark(struct page_counter *counter)
> counter->watermark = page_counter_read(counter);
> }
>
> +static inline void page_counter_reset_local_watermark(struct page_counter *counter)
> +{
> + counter->local_watermark = page_counter_read(counter);
> +}
> +
> #endif /* _LINUX_PAGE_COUNTER_H */
> diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
> index 520b90dd97ec..5a97ba08e976 100644
> --- a/kernel/cgroup/cgroup-internal.h
> +++ b/kernel/cgroup/cgroup-internal.h
> @@ -81,6 +81,8 @@ struct cgroup_file_ctx {
> struct {
> struct cgroup_pidlist *pidlist;
> } procs1;
> +
> + struct memcg_peak_mem_ctx peak;
> };
>
> /*
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index e32b6972c478..38b935ffa6cf 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -1964,6 +1964,13 @@ static int cgroup2_parse_param(struct fs_context *fc, struct fs_parameter *param
> return -EINVAL;
> }
>
> +struct memcg_peak_mem_ctx *memcg_extract_peak_mem_ctx(struct kernfs_open_file *of)
> +{
> + struct cgroup_file_ctx *ctx = of->priv;
> +
> + return &ctx->peak;
> +}
> +
> static void apply_cgroup_root_flags(unsigned int root_flags)
> {
> if (current->nsproxy->cgroup_ns == &init_cgroup_ns) {
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 8f2f1bb18c9c..eb6614236371 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>
> @@ -5745,6 +5746,7 @@ static struct mem_cgroup *mem_cgroup_alloc(struct mem_cgroup *parent)
> vmpressure_init(&memcg->vmpressure);
> INIT_LIST_HEAD(&memcg->event_list);
> spin_lock_init(&memcg->event_list_lock);
> + spin_lock_init(&memcg->pagecounter_peak_watchers_lock);
> memcg->socket_pressure = jiffies;
> #ifdef CONFIG_MEMCG_KMEM
> memcg->kmemcg_id = -1;
> @@ -6907,12 +6909,130 @@ static u64 memory_current_read(struct cgroup_subsys_state *css,
> return (u64)page_counter_read(&memcg->memory) * PAGE_SIZE;
> }
>
> -static u64 memory_peak_read(struct cgroup_subsys_state *css,
> - struct cftype *cft)
> +static struct page_counter *memcg_memory_extract_page_counter(struct mem_cgroup *memcg)
> {
> + return &memcg->memory;
> +}
> +
> +static struct memcg_peak_mem_ctx **memcg_memory_extract_peak_watchers(struct mem_cgroup *memcg)
> +{
> + return &memcg->peak_memory_local_watermark_watchers;
> +}
> +
> +inline int swap_memory_peak_show(
> + struct seq_file *sf, void *v,
> + struct page_counter *(*extract_pc)(struct mem_cgroup *memcg))
> +{
> + struct cgroup_subsys_state *css = seq_css(sf);
> struct mem_cgroup *memcg = mem_cgroup_from_css(css);
> + struct page_counter *pc = extract_pc(memcg);
> +
> + struct kernfs_open_file *of = sf->private;
> + struct memcg_peak_mem_ctx *ctx = memcg_extract_peak_mem_ctx(of);
> + s64 fd_peak = ctx->local_watermark;
> +
> + if (fd_peak == -1) {
> + seq_printf(sf, "%llu\n", (u64)pc->watermark * PAGE_SIZE);
> + return 0;
> + }
> +
> + s64 pc_peak = pc->local_watermark;
> + s64 wm = fd_peak > pc_peak ? fd_peak : pc_peak;
> +
> + seq_printf(sf, "%lld\n", wm * PAGE_SIZE);
> + return 0;
> +}
> +
> +static int memory_peak_show(struct seq_file *sf, void *v)
> +{
> + return swap_memory_peak_show(sf, v, memcg_memory_extract_page_counter);
I think it's really too complex. Why not pass a single boolean argument
which will define to use memory page_counter or swap page_counter?
It will eliminate a need to pass pointers to functions and also eliminate
a need for introducing these helper functions in general.
> +}
> +
> +static int swap_memory_peak_open(struct kernfs_open_file *of)
> +{
> + struct memcg_peak_mem_ctx *ctx = memcg_extract_peak_mem_ctx(of);
> +
> + ctx->local_watermark = -1;
> + return 0;
> +}
> +
> +inline void swap_memory_peak_release(
> + struct kernfs_open_file *of,
> + struct memcg_peak_mem_ctx **(*extract_watchers)(struct mem_cgroup *memcg))
> +{
> + struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
> + struct memcg_peak_mem_ctx *ctx = memcg_extract_peak_mem_ctx(of);
> +
> + if (ctx->local_watermark == -1) {
> + /* fast path (no writes on this fd)*/
> + return;
> + }
> + spin_lock(&memcg->pagecounter_peak_watchers_lock);
> + if (ctx->next) {
> + ctx->next->prev = ctx->prev;
> + }
> + if (ctx->prev) {
> + ctx->prev->next = ctx->next;
> + } else {
> + struct memcg_peak_mem_ctx **watchers = extract_watchers(memcg);
> +
> + *watchers = ctx->next;
> + }
> + spin_unlock(&memcg->pagecounter_peak_watchers_lock);
> +}
>
> - return (u64)memcg->memory.watermark * PAGE_SIZE;
> +static void memory_peak_release(struct kernfs_open_file *of)
> +{
> + swap_memory_peak_release(of, memcg_memory_extract_peak_watchers);
> +}
> +
> +inline ssize_t swap_memory_peak_write(
> + struct kernfs_open_file *of,
> + char *buf, size_t nbytes, loff_t off,
> + struct page_counter* (*extract_pc)(struct mem_cgroup *memcg),
> + struct memcg_peak_mem_ctx **(*extract_watchers)(struct mem_cgroup *memcg))
> +{
> + buf = strstrip(buf);
> + /* Only allow "fd_local_reset" to keep the API clear */
> + if (strcmp(buf, "fd_local_reset"))
> + return -EINVAL;
> + struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
> + struct memcg_peak_mem_ctx *ctx = memcg_extract_peak_mem_ctx(of);
Please, don't mix variable definitions and code. Also, please, use
scripts/checkpatch.pl for checking the code before submission. I guess
it will raise several issues in this patch.
> +
> + spin_lock(&memcg->pagecounter_peak_watchers_lock);
> +
> + struct page_counter *pc = extract_pc(memcg);
> +
> + page_counter_reset_local_watermark(pc);
> + const unsigned long cur = pc->local_watermark;
> + struct memcg_peak_mem_ctx **watchers = extract_watchers(memcg);
> + struct memcg_peak_mem_ctx *peer_ctx;
> +
> + for (peer_ctx = *watchers; peer_ctx; peer_ctx = peer_ctx->next) {
> + if (cur > peer_ctx->local_watermark)
> + peer_ctx->local_watermark = cur;
> + }
> + if (ctx->local_watermark == -1) {
> + /* only append to the list if we're not already there */
> + if (peer_ctx) {
> + ctx->prev = peer_ctx;
> + peer_ctx->next = ctx;
> + } else {
> + *watchers = ctx;
> + }
> + }
> + ctx->local_watermark = cur;
> + spin_unlock(&memcg->pagecounter_peak_watchers_lock);
> +
> + return nbytes;
> +}
> +
> +static ssize_t memory_peak_write(struct kernfs_open_file *of, char *buf,
> + size_t nbytes, loff_t off)
> +{
> + return swap_memory_peak_write(of, buf, nbytes, off,
> + memcg_memory_extract_page_counter,
> + memcg_memory_extract_peak_watchers);
> }
>
> static int memory_min_show(struct seq_file *m, void *v)
> @@ -7231,7 +7351,10 @@ static struct cftype memory_files[] = {
> {
> .name = "peak",
> .flags = CFTYPE_NOT_ON_ROOT,
> - .read_u64 = memory_peak_read,
> + .open = swap_memory_peak_open,
> + .release = memory_peak_release,
> + .seq_show = memory_peak_show,
> + .write = memory_peak_write,
> },
> {
> .name = "min",
> @@ -8193,14 +8316,35 @@ static u64 swap_current_read(struct cgroup_subsys_state *css,
> return (u64)page_counter_read(&memcg->swap) * PAGE_SIZE;
> }
>
> -static u64 swap_peak_read(struct cgroup_subsys_state *css,
> - struct cftype *cft)
> +
> +static struct page_counter *memcg_swap_extract_page_counter(struct mem_cgroup *memcg)
> +{
> + return &memcg->swap;
> +}
> +
> +static struct memcg_peak_mem_ctx **memcg_swap_extract_peak_watchers(struct mem_cgroup *memcg)
> {
> - struct mem_cgroup *memcg = mem_cgroup_from_css(css);
> + return &memcg->peak_swap_local_watermark_watchers;
> +}
> +
> +static int swap_peak_show(struct seq_file *sf, void *v)
> +{
> + return swap_memory_peak_show(sf, v, memcg_swap_extract_page_counter);
> +}
>
> - 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)
> +{
> + return swap_memory_peak_write(of, buf, nbytes, off,
> + memcg_swap_extract_page_counter,
> + memcg_swap_extract_peak_watchers);
> +}
> +static void swap_peak_release(struct kernfs_open_file *of)
> +{
> + swap_memory_peak_release(of, memcg_swap_extract_peak_watchers);
> }
>
> +
> static int swap_high_show(struct seq_file *m, void *v)
> {
> return seq_puts_memcg_tunable(m,
> @@ -8282,7 +8426,10 @@ static struct cftype swap_files[] = {
> {
> .name = "swap.peak",
> .flags = CFTYPE_NOT_ON_ROOT,
> - .read_u64 = swap_peak_read,
> + .open = swap_memory_peak_open,
> + .release = swap_peak_release,
> + .seq_show = swap_peak_show,
> + .write = swap_peak_write,
> },
> {
> .name = "swap.events",
> diff --git a/mm/page_counter.c b/mm/page_counter.c
> index db20d6452b71..40d5f4990218 100644
> --- a/mm/page_counter.c
> +++ b/mm/page_counter.c
> @@ -82,6 +82,8 @@ void page_counter_charge(struct page_counter *counter, unsigned long nr_pages)
> */
> if (new > READ_ONCE(c->watermark))
> WRITE_ONCE(c->watermark, new);
> + if (new > READ_ONCE(c->local_watermark))
> + WRITE_ONCE(c->local_watermark, new);
Hm, can't we have a single comparison on the hot path?
Also, we read and write c->local_watermark speculatively here, Idk if it's still
acceptable with an ability to reset watermarks "locally". Maybe it is, but
it definitely deserves at least a comment with an explanation.
And btw thank you for including tests into the commit, it's really great to see.
I'd suggest you to extract them into a separate commit and post it as a series.
Thank you!
