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Message-ID: <20241007163507.647617031@linutronix.de>
Date: Mon, 7 Oct 2024 18:49:51 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Zhen Lei <thunder.leizhen@...wei.com>,
Waiman Long <longman@...hat.com>
Subject: [patch 00/25] debugobjects: Rework object handling
Zhen reported that the global lock in debug objects is problematic. There
are several issues:
1) Parallel pool refill attempts result in long wait times
2) The operations under the lock move batches of objects by moving
them one by one from one list to another
This takes quite some time and is also a cache line dirtying
festival.
For further context see:
https://lore.kernel.org/all/20240904133944.2124-1-thunder.leizhen@huawei.com
https://lore.kernel.org/all/20240904134152.2141-1-thunder.leizhen@huawei.com
Address this with the following changes:
1) Avoid parallel pool refills unless the fill level is critical
2) Release and reacquire the pool look between batches in the worker
thread.
3) Convert the pool handling to a stack of batches which can be moved
with trivial hlist operations which are fast and do not touch a
gazillion of cache lines
While working on this, I noticed that the kmem_cache allocation/free rate
is rather high. This is addressed by:
1) Doubling the per CPU pool size
2) Agressively refilling the per CPU pool from the free list
3) Throttling the kmem_cache_free() operations by monitoring the object
usage with a exponentially wheighed moving average
The resulting reduction for a full kernel compile:
kmem_cache_alloc() kmem_cache_free()
Base: 380k 330k
#1: 295k 245k
#2: 225k 245k
#3: 170k 117k
Especially the reduction of allocations makes a difference as that happens
in the hot path.
There are further possibilities to enhance this:
1) Move the lock into the new global pool data structure
2) Provide a per-node "global" pool which is brought up
before the first CPU of a node is brought up
That's left as an exercise for the reader. :)
The series has incorporated the latest changes from Zhen:
https://lore.kernel.org/all/20240911083521.2257-1-thunder.leizhen@huawei.com
to avoid conflicts.
It is based on v6.12-rc1 and also available from git:
git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git core/debugobjects
Thanks,
tglx
---
include/linux/debugobjects.h | 12
lib/debugobjects.c | 866 ++++++++++++++++++++++++-------------------
2 files changed, 503 insertions(+), 375 deletions(-)
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