| Message ID | 20220425190040.2475377-2-yosryahmed@google.com |
|---|---|
| State | New |
| Headers | show |
| Series | memcg: introduce per-memcg proactive reclaim | expand |
On Mon, 25 Apr 2022, Yosry Ahmed wrote: >From: Shakeel Butt <shakeelb@google.com> > >Introduce a memcg interface to trigger memory reclaim on a memory cgroup. > >Use case: Proactive Reclaim >--------------------------- > >A userspace proactive reclaimer can continuously probe the memcg to >reclaim a small amount of memory. This gives more accurate and >up-to-date workingset estimation as the LRUs are continuously >sorted and can potentially provide more deterministic memory >overcommit behavior. The memory overcommit controller can provide >more proactive response to the changing behavior of the running >applications instead of being reactive. > >A userspace reclaimer's purpose in this case is not a complete replacement >for kswapd or direct reclaim, it is to proactively identify memory savings >opportunities and reclaim some amount of cold pages set by the policy >to free up the memory for more demanding jobs or scheduling new jobs. > >A user space proactive reclaimer is used in Google data centers. >Additionally, Meta's TMO paper recently referenced a very similar >interface used for user space proactive reclaim: >https://dl.acm.org/doi/pdf/10.1145/3503222.3507731 > >Benefits of a user space reclaimer: >----------------------------------- > >1) More flexible on who should be charged for the cpu of the memory >reclaim. For proactive reclaim, it makes more sense to be centralized. > >2) More flexible on dedicating the resources (like cpu). The memory >overcommit controller can balance the cost between the cpu usage and >the memory reclaimed. > >3) Provides a way to the applications to keep their LRUs sorted, so, >under memory pressure better reclaim candidates are selected. This also >gives more accurate and uptodate notion of working set for an >application. > >Why memory.high is not enough? >------------------------------ > >- memory.high can be used to trigger reclaim in a memcg and can > potentially be used for proactive reclaim. > However there is a big downside in using memory.high. It can potentially > introduce high reclaim stalls in the target application as the > allocations from the processes or the threads of the application can hit > the temporary memory.high limit. > >- Userspace proactive reclaimers usually use feedback loops to decide > how much memory to proactively reclaim from a workload. The metrics > used for this are usually either refaults or PSI, and these metrics > will become messy if the application gets throttled by hitting the > high limit. > >- memory.high is a stateful interface, if the userspace proactive > reclaimer crashes for any reason while triggering reclaim it can leave > the application in a bad state. > >- If a workload is rapidly expanding, setting memory.high to proactively > reclaim memory can result in actually reclaiming more memory than > intended. > >The benefits of such interface and shortcomings of existing interface >were further discussed in this RFC thread: >https://lore.kernel.org/linux-mm/5df21376-7dd1-bf81-8414-32a73cea45dd@google.com/ > >Interface: >---------- > >Introducing a very simple memcg interface 'echo 10M > memory.reclaim' to >trigger reclaim in the target memory cgroup. > >The interface is introduced as a nested-keyed file to allow for future >optional arguments to be easily added to configure the behavior of >reclaim. > >Possible Extensions: >-------------------- > >- This interface can be extended with an additional parameter or flags > to allow specifying one or more types of memory to reclaim from (e.g. > file, anon, ..). > >- The interface can also be extended with a node mask to reclaim from > specific nodes. This has use cases for reclaim-based demotion in memory > tiering systens. > >- A similar per-node interface can also be added to support proactive > reclaim and reclaim-based demotion in systems without memcg. > >- Add a timeout parameter to make it easier for user space to call the > interface without worrying about being blocked for an undefined amount > of time. > >For now, let's keep things simple by adding the basic functionality. > >[yosryahmed@google.com: worked on versions v2 onwards, refreshed to >current master, updated commit message based on recent >discussions and use cases] > >Signed-off-by: Shakeel Butt <shakeelb@google.com> >Co-developed-by: Yosry Ahmed <yosryahmed@google.com> >Signed-off-by: Yosry Ahmed <yosryahmed@google.com> >Acked-by: Johannes Weiner <hannes@cmpxchg.org> >Acked-by: Michal Hocko <mhocko@suse.com> >Acked-by: Wei Xu <weixugc@google.com> >Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 69d7a6983f78..19bcd73cad03 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -1208,6 +1208,27 @@ PAGE_SIZE multiple when read back. high limit is used and monitored properly, this limit's utility is limited to providing the final safety net. + memory.reclaim + A write-only nested-keyed file which exists for all cgroups. + + This is a simple interface to trigger memory reclaim in the + target cgroup. + + This file accepts a single key, the number of bytes to reclaim. + No nested keys are currently supported. + + Example:: + + echo "1G" > memory.reclaim + + The interface can be later extended with nested keys to + configure the reclaim behavior. For example, specify the + type of memory to reclaim from (anon, file, ..). + + Please note that the kernel can over or under reclaim from + the target cgroup. If less bytes are reclaimed than the + specified amount, -EAGAIN is returned. + memory.oom.group A read-write single value file which exists on non-root cgroups. The default value is "0". diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 725f76723220..879f1716d6e9 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -6355,6 +6355,46 @@ static ssize_t memory_oom_group_write(struct kernfs_open_file *of, return nbytes; } +static ssize_t memory_reclaim(struct kernfs_open_file *of, char *buf, + size_t nbytes, loff_t off) +{ + struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of)); + unsigned int nr_retries = MAX_RECLAIM_RETRIES; + unsigned long nr_to_reclaim, nr_reclaimed = 0; + int err; + + buf = strstrip(buf); + err = page_counter_memparse(buf, "", &nr_to_reclaim); + if (err) + return err; + + while (nr_reclaimed < nr_to_reclaim) { + unsigned long reclaimed; + + if (signal_pending(current)) + return -EINTR; + + /* + * This is the final attempt, drain percpu lru caches in the + * hope of introducing more evictable pages for + * try_to_free_mem_cgroup_pages(). + */ + if (!nr_retries) + lru_add_drain_all(); + + reclaimed = try_to_free_mem_cgroup_pages(memcg, + nr_to_reclaim - nr_reclaimed, + GFP_KERNEL, true); + + if (!reclaimed && !nr_retries--) + return -EAGAIN; + + nr_reclaimed += reclaimed; + } + + return nbytes; +} + static struct cftype memory_files[] = { { .name = "current", @@ -6413,6 +6453,11 @@ static struct cftype memory_files[] = { .seq_show = memory_oom_group_show, .write = memory_oom_group_write, }, + { + .name = "reclaim", + .flags = CFTYPE_NS_DELEGATABLE, + .write = memory_reclaim, + }, { } /* terminate */ };