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bh=X+DqdrS6iCcxvyTC6yHwsLzPqdZ3ScxxXhmioABziL4=; b=11WREbQryZUB+6p/3Jnhtn2e+EGl3o06ZWfAXA1h0H1up/FJTI7o3WCEpby82DYhOEamIS SNo2GK1/pjwtMbvsFMlr0TeRU0EO2A+Fob5UolLo5fyZftXjxYAa7SO9WFuwezd7crzVt4 V6loaNbJSNtaumAwHLxJ4CyXzfNeOOATPRyRwxdc3lBCyKZUeuMlrLoe4pat2v5sQn1Lf6 qbdUi/sofYbeUxf/c5vZJ7x9ujrfqlksMvcuC4B3WSIwGV6H8RqiL+2iP5jD/cPyfo2H73 7vHup3RTQ8ofFdfjsOAd2iXE8Qox2izdP8O3JcFXW8nnN1cVeg8hTEwitHVe4Q== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1728297829; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=X+DqdrS6iCcxvyTC6yHwsLzPqdZ3ScxxXhmioABziL4=; b=uuaUDwkDAkRjg0n1+IyVHh3x7rt9v9AOYpm9kk/cF5bQzmwmEIfZ4jyBkZiosa1SZQpS9i zt/Bh/pYeLtUM0BQ== From: Sebastian Andrzej Siewior To: Arnd Bergmann Cc: Dennis Zhou , Tejun Heo , Christoph Lameter , Thomas Gleixner , Will Deacon , Arnd Bergmann , kernel test robot , Andrew Morton , Suren Baghdasaryan , Kent Overstreet , Hou Tao , Jan Kara , Jianhui Zhou <912460177@qq.com>, Yury Norov , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] preempt_rt: increase PERCPU_DYNAMIC_SIZE_SHIFT for slab randomization Message-ID: <20241007104348.ImJPXDl9@linutronix.de> References: <20241004095702.637528-1-arnd@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20241004095702.637528-1-arnd@kernel.org> X-Stat-Signature: amseku6ph9qsbwx584hf15srpdnsq3c5 X-Rspamd-Queue-Id: 271A28000E X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1728297831-830350 X-HE-Meta: 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 9jpRTi93 3u7dTBTog73RwwcaBt+UI5IXFFtwlL5XXpTDt081xgsZkaq8KyXcga26oqfsi+5zwIakOQvt7oQMSB6dg9UTZ7vYuCklxOQq4F16VxotOZusrzQQ1Xzq4IV8xpX9AEoPSLv5LvwWFvprY5OpNwWOFiJ52ynxQrnYOhj1rXrpn+RAMRtCQUwy/cqmN7ZaZBvySC2/amaZlg6PDB18y5WM8I6jQW2THsdBHW2OcbnS82ChNWDGzQDF2tld1muUvdXYmOUXZqpL6evDyLqpINbTe4OMLfg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2024-10-04 09:56:56 [+0000], Arnd Bergmann wrote: > The problem is the additional size overhead from local_lock in > struct kmem_cache_cpu. Avoid this by preallocating a larger area. The worst case would be enabling additionally MEMCG so NR_KMALLOC_TYPES increases by one. And then we have: PERCPU_DYNAMIC_EARLY_SIZE < NR_KMALLOC_TYPES * KMALLOC_SHIFT_HIGH * sizeof(struct kmem_cache_cpu)); There is more to it than just RANDOM_KMALLOC_CACHES and PREEMPT_RT. There is additionally CONFIG_LOCKDEP which increases the size of local_lock_t further. Plus CONFIG_LOCK_STAT. The last one a kind of bad in terms of required pad area. Then we have CONFIG_PAGE_SIZE_64KB set which is the culprit. But 16K_PAGES also fail in this full blown case. PERCPU_DYNAMIC_EARLY_SIZE < NR_KMALLOC_TYPES * KMALLOC_SHIFT_HIGH * sizeof(struct kmem_cache_cpu)); 4KiB 20 << 12 < 19 * (12 + 1) * 288 80KiB < 69.46875 16KiB 20 << 12 < 19 * (14 + 1) * 288 80KiB < 80.15625 64KiB 20 << 12 < 19 * (16 + 1) * 288 80KiB < 90.84375 128KiB 20 << 12 < 19 * (17 + 1) * 288 80KiB < 96.1875 Just disabling CONFIG_LOCK_STAT the 16KiB PAGE_SIZE case works again (75.703125), the 64KiB still fails (85.796875). > There is a good chance that there is a better way to address this, this > version was the first I came up with and I verified that it fixes all of > the broken configs. How bad is it, to have PERCPU_DYNAMIC_SIZE_SHIFT unconditionally set to 13? If it is bad could we restrict it with LOCKDEP and PAGE_SIZE > 4KiB? So maybe something like this: diff --git a/include/linux/percpu.h b/include/linux/percpu.h index b6321fc491598..52b5ea663b9f0 100644 --- a/include/linux/percpu.h +++ b/include/linux/percpu.h @@ -41,7 +41,11 @@ PCPU_MIN_ALLOC_SHIFT) #ifdef CONFIG_RANDOM_KMALLOC_CACHES -#define PERCPU_DYNAMIC_SIZE_SHIFT 12 +# if defined(CONFIG_LOCKDEP) && !defined(CONFIG_PAGE_SIZE_4KB) +# define PERCPU_DYNAMIC_SIZE_SHIFT 13 +# else +# define PERCPU_DYNAMIC_SIZE_SHIFT 12 +#endif /* LOCKDEP and PAGE_SIZE > 4KiB */ #else #define PERCPU_DYNAMIC_SIZE_SHIFT 10 #endif Sebastian