On Wed, Feb 26, 2020 at 3:59 PM Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> wrote: > > > > On 2/26/20 12:25 PM, Shakeel Butt wrote: > > On Wed, Feb 19, 2020 at 10:12 AM Johannes Weiner <hannes@xxxxxxxxxxx> wrote: > >> We have received regression reports from users whose workloads moved > >> into containers and subsequently encountered new latencies. For some > >> users these were a nuisance, but for some it meant missing their SLA > >> response times. We tracked those delays down to cgroup limits, which > >> inject direct reclaim stalls into the workload where previously all > >> reclaim was handled my kswapd. > >> > >> This patch adds asynchronous reclaim to the memory.high cgroup limit > >> while keeping direct reclaim as a fallback. In our testing, this > >> eliminated all direct reclaim from the affected workload. > >> > >> memory.high has a grace buffer of about 4% between when it becomes > >> exceeded and when allocating threads get throttled. We can use the > >> same buffer for the async reclaimer to operate in. If the worker > >> cannot keep up and the grace buffer is exceeded, allocating threads > >> will fall back to direct reclaim before getting throttled. > >> > >> For irq-context, there's already async memory.high enforcement. Re-use > >> that work item for all allocating contexts, but switch it to the > >> unbound workqueue so reclaim work doesn't compete with the workload. > >> The work item is per cgroup, which means the workqueue infrastructure > >> will create at maximum one worker thread per reclaiming cgroup. > >> > >> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> > >> --- > >> mm/memcontrol.c | 60 +++++++++++++++++++++++++++++++++++++------------ > >> mm/vmscan.c | 10 +++++++-- > > This reminds me of the per-memcg kswapd proposal from LSFMM 2018 > > (https://lwn.net/Articles/753162/). > > Thanks for bringing this up. > > > > > If I understand this correctly, the use-case is that the job instead > > of direct reclaiming (potentially in latency sensitive tasks), prefers > > a background non-latency sensitive task to do the reclaim. I am > > wondering if we can use the memory.high notification along with a new > > memcg interface (like memory.try_to_free_pages) to implement a user > > space background reclaimer. That would resolve the cpu accounting > > concerns as the user space background reclaimer can share the cpu cost > > with the task. > > Actually I'm interested how you implement userspace reclaimer. Via a new > syscall or a variant of existing syscall? > We have a per-memcg interface memory.try_to_free_pages on which user space can echo two numbers i.e. number of bytes to reclaim and a byte representing flags (I/O allowed or just reclaim zombies e.t.c). However nowadays we are just using it for zombie cleanup. Shakeel
