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SubjectRe: [PATCH-next 2/5] lib/test_vmalloc.c: add a new 'nr_threads' parameter
> On Fri,  2 Apr 2021 22:22:34 +0200 "Uladzislau Rezki (Sony)" <urezki@gmail.com> wrote:
>
> > By using this parameter we can specify how many workers are
> > created to perform vmalloc tests. By default it is one CPU.
> > The maximum value is set to 1024.
> >
> > As a result of this change a 'single_cpu_test' one becomes
> > obsolete, therefore it is no longer needed.
> >
>
> Why limit to 1024? Maybe testers want more - what's the downside to
> permitting that?
>
I was thinking mainly about if a tester issues enormous number of kthreads,
so a system is not able to handle it. Therefore i clamped that value to 1024.

From the other hand we can give more wide permissions, in that case a
user should think more carefully about what is passed. For example we
can limit max value by USHRT_MAX what is 65536.

>
> We may need to replaced that kcalloc() with kmvalloc() though...
>
Yep. If we limit to USHRT_MAX, the maximum amount of memory for
internal data would be ~12MB. Something like below:

diff --git a/lib/test_vmalloc.c b/lib/test_vmalloc.c
index d337985e4c5e..a5103e3461bf 100644
--- a/lib/test_vmalloc.c
+++ b/lib/test_vmalloc.c
@@ -24,7 +24,7 @@
MODULE_PARM_DESC(name, msg) \

__param(int, nr_threads, 0,
- "Number of workers to perform tests(min: 1 max: 1024)");
+ "Number of workers to perform tests(min: 1 max: 65536)");

__param(bool, sequential_test_order, false,
"Use sequential stress tests order");
@@ -469,13 +469,13 @@ init_test_configurtion(void)
{
/*
* A maximum number of workers is defined as hard-coded
- * value and set to 1024. We add such gap just in case
+ * value and set to 65536. We add such gap just in case
* and for potential heavy stressing.
*/
- nr_threads = clamp(nr_threads, 1, 1024);
+ nr_threads = clamp(nr_threads, 1, 65536);

/* Allocate the space for test instances. */
- tdriver = kcalloc(nr_threads, sizeof(*tdriver), GFP_KERNEL);
+ tdriver = kvcalloc(nr_threads, sizeof(*tdriver), GFP_KERNEL);
if (tdriver == NULL)
return -1;

@@ -555,7 +555,7 @@ static void do_concurrent_test(void)
i, t->stop - t->start);
}

- kfree(tdriver);
+ kvfree(tdriver);
}

static int vmalloc_test_init(void)
Does it sound reasonable for you?

--
Vlad Rezki

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