linux-kernel - Re: mm: percpu: increase PERCPU_MODULE_RESERVE to avoid allocation failure

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Message-Id: <20250422170209.a8beaa8a3610d2e92421476f@linux-foundation.org>
Date: Tue, 22 Apr 2025 17:02:09 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: gaoxu <gaoxu2@...or.com>
Cc: Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>, Christoph
 Lameter <cl@...ux.com>, "linux-mm@...ck.org" <linux-mm@...ck.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "surenb@...gle.com" <surenb@...gle.com>, yipengxiang
 <yipengxiang@...or.com>
Subject: Re: mm: percpu: increase PERCPU_MODULE_RESERVE to avoid allocation
 failure

On Tue, 22 Apr 2025 11:39:30 +0000 gaoxu <gaoxu2@...or.com> wrote:

> In android16-6.12, enabling CONFIG_MEM_ALLOC_PROFILING causes some modules
> to fail to load during boot because of failed percpu memory allocation.

Which modules?  If they're in-tree modules then we should fix this
issue in -stable kernels also.

If they're out-of-tree modules then what argument is there for altering
the mainline kernel?

> [811:modprobe]percpu: allocation failed, size=5200 align=8 atomic=0, alloc
> from reserved chunk failed
> [811:modprobe]Call trace:
> [811:modprobe] dump_backtrace+0xfc/0x17c
> [811:modprobe] show_stack+0x18/0x28
> [811:modprobe] dump_stack_lvl+0x40/0xc0
> [811:modprobe] dump_stack+0x18/0x24
> [811:modprobe] pcpu_alloc_noprof+0x96c/0xb58
> [811:modprobe] percpu_modalloc+0x50/0xec
> [811:modprobe] load_module+0x1158/0x153c
> [811:modprobe] __arm64_sys_finit_module+0x23c/0x340
> [811:modprobe] invoke_syscall+0x58/0x10c
> [811:modprobe] el0_svc_common+0xa8/0xdc
> [811:modprobe] do_el0_svc+0x1c/0x28
> [811:modprobe] el0_svc+0x40/0x90
> [811:modprobe] el0t_64_sync_handler+0x70/0xbc
> [811:modprobe] el0t_64_sync+0x1a8/0x1ac
> [811:modprobe]ipam: Could not allocate 5200 bytes percpu data
> 
> Increase PERCPU_MODULE_RESERVE to resolve this issue.
> 
> ...
>
> --- a/include/linux/percpu.h
> +++ b/include/linux/percpu.h
> @@ -16,7 +16,7 @@
>  /* enough to cover all DEFINE_PER_CPUs in modules */
>  #ifdef CONFIG_MODULES
>  #ifdef CONFIG_MEM_ALLOC_PROFILING
> -#define PERCPU_MODULE_RESERVE		(8 << 13)
> +#define PERCPU_MODULE_RESERVE		(8 << 14)
>  #else
>  #define PERCPU_MODULE_RESERVE		(8 << 10)
>  #endif

PERCPU_MODULE_RESERVE is a pretty unpleasant thing.  It appears that it
gives us the choice between either wasting memory or failing module
loading.  But I expect that something more dynamic would be a ton of work.