Re: [LTP] getrusage03: account for percpu RSS counter batching

[linuxtestproject.agent@gmail.com]

Hi Nirmoy,

On Aug 25, 2026, Nirmoy Das wrote:
> getrusage03: account for percpu RSS counter batching

> +	long batch = MAX(32L, tst_ncpus() * 2);
> +	long delta = MAXRSS_BATCHES * batch * SAFE_SYSCONF(_SC_PAGESIZE) / 1024;

Could this allowance also scale by the number of online CPUs? An mm's
anonymous RSS counter can retain up to batch - 1 pages on every CPU visited
by the child, and task migration does not flush the previous CPU's local
counter. Linux's own error bound in __percpu_counter_compare() is
batch * num_online_cpus().

For example, with 64 online CPUs and 4 KiB pages, the batch is 128 pages.
This code computes 1 MiB and therefore retains the old 20 MiB floor, while
partial batches on 41 CPUs can already omit more than 20 MiB. The failure
this patch intends to address therefore remains possible.

Verdict - Needs revision

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