[PATCH v1 0/5] mm: improve performance of accounted kernel memory allocations

Roman Gushchin
2023-09-29T18:01:20Z

This patchset improves the performance of accounted kernel memory allocations
by ~30% as measured by a micro-benchmark [1]. The benchmark is very
straightforward: 1M of 64 bytes-large kmalloc() allocations.

Below are results with the disabled kernel memory accounting, the original state
and with this patchset applied.

| | Kmem disabled | Original | Patched | Delta |
|-------------+---------------+----------+---------+--------|
| User cgroup | 29764 | 84548 | 59078 | -30.0% |
| Root cgroup | 29742 | 48342 | 31501 | -34.8% |

As we can see, the patchset removes the majority of the overhead when there is
no actual accounting (a task belongs to the root memory cgroup) and almost
halves the accounting overhead otherwise.

The main idea is to get rid of unnecessary memcg to objcg conversions and switch
to a scope-based protection of objcgs, which eliminates extra operations with
objcg reference counters under a rcu read lock. More details are provided in
individual commit descriptions.

v1:
- made the objcg update fully lockless
- fixed !CONFIG_MMU build issues
rfc:
https://lwn.net/Articles/945722/

--
[1]:

static int memory_alloc_test(struct seq_file *m, void *v)
{
unsigned long i, j;
void **ptrs;
ktime_t start, end;
s64 delta, min_delta = LLONG_MAX;

ptrs = kvmalloc(sizeof(void *) * 1000000, GFP_KERNEL);
if (!ptrs)
return -ENOMEM;

for (j = 0; j < 100; j++) {
start = ktime_get();
for (i = 0; i < 1000000; i++)
ptrs[i] = kmalloc(64, GFP_KERNEL_ACCOUNT);
end = ktime_get();

delta = ktime_us_delta(end, start);
if (delta < min_delta)
min_delta = delta;

for (i = 0; i < 1000000; i++)
kfree(ptrs[i]);
}

kvfree(ptrs);
seq_printf(m, "%lld us\n", min_delta);

return 0;
}

--

Signed-off-by: Roman Gushchin (Cruise) <roman.gushchin@linux.dev>

Roman Gushchin (5):
mm: kmem: optimize get_obj_cgroup_from_current()
mm: kmem: add direct objcg pointer to task_struct
mm: kmem: make memcg keep a reference to the original objcg
mm: kmem: scoped objcg protection
percpu: scoped objcg protection

include/linux/memcontrol.h | 24 ++++-
include/linux/sched.h | 4 +
mm/memcontrol.c | 184 ++++++++++++++++++++++++++++++++-----
mm/percpu.c | 8 +-
mm/slab.h | 10 +-
5 files changed, 192 insertions(+), 38 deletions(-)

--
2.42.0