linux-kernel - Re: [PATCH v10 2/3] mm: Fix OOM killer inaccuracy on large many-core systems

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Message-ID: <2fb78e41-5e56-425f-925f-a29524355d2c@efficios.com>
Date: Fri, 19 Dec 2025 11:01:11 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Mark Brown <broonie@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
 "Paul E. McKenney" <paulmck@...nel.org>, Steven Rostedt
 <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>,
 Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
 Christoph Lameter <cl@...ux.com>, Martin Liu <liumartin@...gle.com>,
 David Rientjes <rientjes@...gle.com>, christian.koenig@....com,
 Shakeel Butt <shakeel.butt@...ux.dev>, SeongJae Park <sj@...nel.org>,
 Michal Hocko <mhocko@...e.com>, Johannes Weiner <hannes@...xchg.org>,
 Sweet Tea Dorminy <sweettea-kernel@...miny.me>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R . Howlett" <liam.howlett@...cle.com>, Mike Rapoport
 <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Christian Brauner <brauner@...nel.org>,
 Wei Yang <richard.weiyang@...il.com>, David Hildenbrand <david@...hat.com>,
 Miaohe Lin <linmiaohe@...wei.com>, Al Viro <viro@...iv.linux.org.uk>,
 linux-mm@...ck.org, linux-trace-kernel@...r.kernel.org,
 Yu Zhao <yuzhao@...gle.com>, Roman Gushchin <roman.gushchin@...ux.dev>,
 Mateusz Guzik <mjguzik@...il.com>, Matthew Wilcox <willy@...radead.org>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Aboorva Devarajan <aboorvad@...ux.ibm.com>,
 Aishwarya TCV <Aishwarya.TCV@....com>
Subject: Re: [PATCH v10 2/3] mm: Fix OOM killer inaccuracy on large many-core
 systems

On 2025-12-19 04:31, Mark Brown wrote:
> On Thu, Dec 18, 2025 at 05:18:04PM -0500, Mathieu Desnoyers wrote:
>> On 2025-12-18 13:00, Mark Brown wrote:
> 
>> An ugly work-around that may work (and then we can improve on this),
>> at the end of mm/init-mm.c:init_mm (completely untested):
> 
>>         .cpu_bitmap     = { [0 ... ((3*BITS_TO_LONGS(NR_CPUS))-1 + ((69905 * NR_MM_COUNTERS * 64) / BYTES_PER_LONG))] = 0UL },
> 
> That doesn't seem to fix the FVP unfortunately (BYTES_PER_LONG doesn't
> exist, but even just deleting the division entirely fails in the same
> way).

I just noticed that there is another static instance of mm_struct:

drivers/firmware/efi/efi.c struct mm_struct efi_mm

we need to apply the same fix to it as well. It seems to fit
with the currently running task when the oops happens:

[    2.482454] CPU: 2 UID: 0 PID: 12 Comm: kworker/u32:0 Not tainted 6.19.0-rc1-next-20251218 #1 PREEMPT
[    2.482609] Workqueue: efi_rts_wq efi_call_rts

[...]
[    2.485094]  acct_account_cputime+0x40/0xa4 (P)
[...]
[    2.487172]  el1h_64_irq+0x6c/0x70
[...]
[    2.487853]  __efi_rt_asm_wrapper+0x50/0x74

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com