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author | Brian Chen <brianchen118@gmail.com> | 2021-11-11 00:33:12 +0300 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-01-27 13:04:27 +0300 |
commit | d168123f1388882bf5b41d07e5534a319f5fff1a (patch) | |
tree | cf56dc7baf840fdffda405f6fc96ee105fb6d7bb /include/linux | |
parent | 07888a4fbcf23dd79c2e361ded5b9bd98e881a7f (diff) | |
download | linux-d168123f1388882bf5b41d07e5534a319f5fff1a.tar.xz |
psi: Fix PSI_MEM_FULL state when tasks are in memstall and doing reclaim
[ Upstream commit cb0e52b7748737b2cf6481fdd9b920ce7e1ebbdf ]
We've noticed cases where tasks in a cgroup are stalled on memory but
there is little memory FULL pressure since tasks stay on the runqueue
in reclaim.
A simple example involves a single threaded program that keeps leaking
and touching large amounts of memory. It runs in a cgroup with swap
enabled, memory.high set at 10M and cpu.max ratio set at 5%. Though
there is significant CPU pressure and memory SOME, there is barely any
memory FULL since the task enters reclaim and stays on the runqueue.
However, this memory-bound task is effectively stalled on memory and
we expect memory FULL to match memory SOME in this scenario.
The code is confused about memstall && running, thinking there is a
stalled task and a productive task when there's only one task: a
reclaimer that's counted as both. To fix this, we redefine the
condition for PSI_MEM_FULL to check that all running tasks are in an
active memstall instead of checking that there are no running tasks.
case PSI_MEM_FULL:
- return unlikely(tasks[NR_MEMSTALL] && !tasks[NR_RUNNING]);
+ return unlikely(tasks[NR_MEMSTALL] &&
+ tasks[NR_RUNNING] == tasks[NR_MEMSTALL_RUNNING]);
This will capture reclaimers. It will also capture tasks that called
psi_memstall_enter() and are about to sleep, but this should be
negligible noise.
Signed-off-by: Brian Chen <brianchen118@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Link: https://lore.kernel.org/r/20211110213312.310243-1-brianchen118@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'include/linux')
-rw-r--r-- | include/linux/psi_types.h | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h index 0a23300d49af..0819c82dba92 100644 --- a/include/linux/psi_types.h +++ b/include/linux/psi_types.h @@ -21,7 +21,17 @@ enum psi_task_count { * don't have to special case any state tracking for it. */ NR_ONCPU, - NR_PSI_TASK_COUNTS = 4, + /* + * For IO and CPU stalls the presence of running/oncpu tasks + * in the domain means a partial rather than a full stall. + * For memory it's not so simple because of page reclaimers: + * they are running/oncpu while representing a stall. To tell + * whether a domain has productivity left or not, we need to + * distinguish between regular running (i.e. productive) + * threads and memstall ones. + */ + NR_MEMSTALL_RUNNING, + NR_PSI_TASK_COUNTS = 5, }; /* Task state bitmasks */ @@ -29,6 +39,7 @@ enum psi_task_count { #define TSK_MEMSTALL (1 << NR_MEMSTALL) #define TSK_RUNNING (1 << NR_RUNNING) #define TSK_ONCPU (1 << NR_ONCPU) +#define TSK_MEMSTALL_RUNNING (1 << NR_MEMSTALL_RUNNING) /* Resources that workloads could be stalled on */ enum psi_res { |