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Message-Id: <20230823050609.2228718-1-mjguzik@gmail.com>
Date: Wed, 23 Aug 2023 07:06:07 +0200
From: Mateusz Guzik <mjguzik@...il.com>
To: linux-kernel@...r.kernel.org
Cc: dennis@...nel.org, tj@...nel.org, cl@...ux.com,
akpm@...ux-foundation.org, shakeelb@...gle.com,
vegard.nossum@...cle.com, linux-mm@...ck.org,
Mateusz Guzik <mjguzik@...il.com>
Subject: [PATCH v3 0/2] execve scalability issues, part 1
To start I figured I'm going to bench about as friendly case as it gets
-- statically linked *separate* binaries all doing execve in a loop.
I borrowed the bench from here:
http://apollo.backplane.com/DFlyMisc/doexec.c
$ cc -static -O2 -o static-doexec doexec.c
$ ./static-doexec $(nproc)
It prints a result every second.
My test box is temporarily only 26 cores and even at this scale I run
into massive lock contention stemming from back-to-back calls to
percpu_counter_init (and _destroy later).
While not a panacea, one simple thing to do here is to batch these ops.
Since the term "batching" is already used in the file, I decided to
refer to it as "grouping" instead.
Even if this code could be patched to dodge these counters, I would
argue a high-traffic alloc/free consumer is only a matter of time so it
makes sense to facilitate it.
With the fix I get an ok win, to quote from the commit:
> Even at a very modest scale of 26 cores (ops/s):
> before: 133543.63
> after: 186061.81 (+39%)
While with the patch these allocations remain a significant problem,
the primary bottleneck shifts to:
__pv_queued_spin_lock_slowpath+1
_raw_spin_lock_irqsave+57
folio_lruvec_lock_irqsave+91
release_pages+590
tlb_batch_pages_flush+61
tlb_finish_mmu+101
exit_mmap+327
__mmput+61
begin_new_exec+1245
load_elf_binary+712
bprm_execve+644
do_execveat_common.isra.0+429
__x64_sys_execve+50
do_syscall_64+46
entry_SYSCALL_64_after_hwframe+110
I intend to do more work on the area to mostly sort it out, but I would
not mind if someone else took the hammer to folio. :)
With this out of the way I'll be looking at some form of caching to
eliminate these allocs as a problem.
v3:
- fix !CONFIG_SMP build
- drop the backtrace from fork commit message
v2:
- force bigger alignment on alloc
- rename "counters" to "nr_counters" and pass prior to lock key
- drop {}'s for single-statement loops
Mateusz Guzik (2):
pcpcntr: add group allocation/free
fork: group allocation of per-cpu counters for mm struct
include/linux/percpu_counter.h | 39 ++++++++++++++++++----
kernel/fork.c | 14 ++------
lib/percpu_counter.c | 61 +++++++++++++++++++++++-----------
3 files changed, 77 insertions(+), 37 deletions(-)
--
2.41.0
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