linux-kernel - Re: [PATCH v8 04/23] slab: add sheaf support for batching kfree

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Message-ID: <cec33567-57cd-44fb-be9b-1bc86f9b30bd@suse.cz>
Date: Thu, 27 Nov 2025 14:18:02 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Jon Hunter <jonathanh@...dia.com>, Daniel Gomez <da.gomez@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Christoph Lameter <cl@...two.org>, David Rientjes <rientjes@...gle.com>
Cc: Roman Gushchin <roman.gushchin@...ux.dev>,
 Harry Yoo <harry.yoo@...cle.com>, Uladzislau Rezki <urezki@...il.com>,
 Sidhartha Kumar <sidhartha.kumar@...cle.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, rcu@...r.kernel.org,
 maple-tree@...ts.infradead.org, linux-modules@...r.kernel.org,
 Luis Chamberlain <mcgrof@...nel.org>, Petr Pavlu <petr.pavlu@...e.com>,
 Sami Tolvanen <samitolvanen@...gle.com>, Aaron Tomlin <atomlin@...mlin.com>,
 Lucas De Marchi <lucas.demarchi@...el.com>,
 "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v8 04/23] slab: add sheaf support for batching kfree_rcu()
 operations

On 11/27/25 12:38, Jon Hunter wrote:
> 
> 
> On 31/10/2025 21:32, Daniel Gomez wrote:
>> 
>> 
>> On 10/09/2025 10.01, Vlastimil Babka wrote:
>> 
>> Hi Vlastimil,
>> 
>> This patch increases kmod selftest (stress module loader) runtime by about
>> ~50-60%, from ~200s to ~300s total execution time. My tested kernel has
>> CONFIG_KVFREE_RCU_BATCHED enabled. Any idea or suggestions on what might be
>> causing this, or how to address it?
>> 
> 
> I have been looking into a regression for Linux v6.18-rc where time 
> taken to run some internal graphics tests on our Tegra234 device has 
> increased from around 35% causing the tests to timeout. Bisect is 
> pointing to this commit and I also see we have CONFIG_KVFREE_RCU_BATCHED=y.

Do the tegra tests involve (frequent) module unloads too, then? Or calling
kmem_cache_destroy() somewhere?

Thanks,
Vlastimil

> I have not tried disabling CONFIG_KVFREE_RCU_BATCHED=y but I can. I am 
> not sure if there are any downsides to disabling this?
> 
> Thanks
> Jon
>