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Subject: Re: [PATCH 1/2] kselftests: cgroup: update kmem test tolerance for multi-memcg stock
Date: Wed, 15 Apr 2026 11:03:56 +0000
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>Hello Xiaokai.
>
>On Tue, Apr 14, 2026 at 11:05:23AM +0000, ranxiaokai627@163.com wrote:
>> Fixes: f735eebe55f8 ("memcg: multi-memcg percpu charge cache")
>
>An interesting catch.
>
>> -#define MAX_VMSTAT_ERROR (4096 * 64 * get_nprocs())
>> +#define NR_MEMCG_STOCK 7
>> +#define MAX_VMSTAT_ERROR (4096 * 64 * NR_MEMCG_STOCK * get_nprocs())
>
>When you touch this, I think this could be factored into it too:
>
>+#define MAX_VMSTAT_ERROR (sysconf(_SC_PAGESIZE) * 64 * NR_MEMCG_STOCK * get_nprocs())

Thanks for the review, yes, this will improve the test' portability
across architectures with different page sizes.

>And given how much the selftest depends in this implementation
>detail(?), I see that there are other selftests that include directly
>from the tree, I'd suggest also
>#include "../../../../include/linux/memcontrol.h"
>
>and use the constant from there (i.e. move NR_MEMCG_STOCK to there too).
>
>That should make the selftest more flexible, resilient to future changes
>and it'd document ramification of these constants too.

Agreed. Including memcontrol.h ensures the test stays in sync with
kernel changes.

>Thanks,
>Michal