linux-kernel - Re: [RFC PATCH 0/2] improve vmalloc allocation

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Date:   Tue, 23 Oct 2018 09:02:56 -0600
From:   Shuah Khan <shuah@...nel.org>
To:     Michal Hocko <mhocko@...nel.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Kees Cook <keescook@...omium.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joelaf@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>, Tejun Heo <tj@...nel.org>,
        Shuah Khan <shuah@...nel.org>
Subject: Re: [RFC PATCH 0/2] improve vmalloc allocation

Hi Michal,

On 10/23/2018 01:23 AM, Michal Hocko wrote:
> Hi Shuah,
> 
> On Mon 22-10-18 18:52:53, Uladzislau Rezki wrote:
>> On Mon, Oct 22, 2018 at 02:51:42PM +0200, Michal Hocko wrote:
>>> Hi,
>>> I haven't read through the implementation yet but I have say that I
>>> really love this cover letter. It is clear on intetion, it covers design
>>> from high level enough to start discussion and provides a very nice
>>> testing coverage. Nice work!
>>>
>>> I also think that we need a better performing vmalloc implementation
>>> long term because of the increasing number of kvmalloc users.
>>>
>>> I just have two mostly workflow specific comments.
>>>
>>>> A test-suite patch you can find here, it is based on 4.18 kernel.
>>>> ftp://vps418301.ovh.net/incoming/0001-mm-vmalloc-stress-test-suite-v4.18.patch
>>>
>>> Can you fit this stress test into the standard self test machinery?
>>>
>> If you mean "tools/testing/selftests", then i can fit that as a kernel module.
>> But not all the tests i can trigger from kernel module, because 3 of 8 tests
>> use __vmalloc_node_range() function that is not marked as EXPORT_SYMBOL.
> 
> Is there any way to conditionally export these internal symbols just for
> kselftests? Or is there any other standard way how to test internal
> functionality that is not exported to modules?
> 

The way it can be handled is by adding a test module under lib. test_kmod,
test_sysctl, test_user_copy etc.

There is a corresponding test script e.g selftests/kmod/kmod.sh that loads
the module and runs tests.

Take a look at lib/test_overflow.c - It is running some vmalloc_node tests
test_overflow.c:DEFINE_TEST_ALLOC(vmalloc_node,  vfree,	     0, 0, 1);
test_overflow.c:DEFINE_TEST_ALLOC(kvmalloc_node, kvfree,     0, 1, 1);
test_overflow.c:	err |= test_kvmalloc_node(NULL);
test_overflow.c:	err |= test_vmalloc_node(NULL);

This module could be extended to tun these stress tests perhaps? I don't see a
selftests test script for test_overflow, one could be added.

Adding Kees Cook to the thread for input on test_overflow.

thanks,
-- Shuah