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

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Message-ID: <8dd08cb4-b7a4-49c8-be16-fc6443daab05@nvidia.com>
Date: Fri, 28 Nov 2025 08:59:38 +0000
From: Jon Hunter <jonathanh@...dia.com>
To: Vlastimil Babka <vbabka@...e.cz>, 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 27/11/2025 13:18, Vlastimil Babka wrote:
> 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?

In this specific case I am not running the tegra-tests but we have a 
internal testsuite of GPU related tests. I don't believe that believe 
this is unloading any modules. I can take a look next week to see if 
kmem_cache_destroy() is getting called somewhere when these tests run.

Thanks
Jon

-- 
nvpublic