linux-kernel - Re: [PATCH-next 2/5] lib/test_vmalloc.c: add a new 'nr

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Date:   Sat, 3 Apr 2021 14:31:43 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     "Uladzislau Rezki (Sony)" <urezki@...il.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Hillf Danton <hdanton@...a.com>,
        Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [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@...il.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