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

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Date:   Mon, 22 Oct 2018 14:51:42 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     "Uladzislau Rezki (Sony)" <urezki@...il.com>
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>
Subject: Re: [RFC PATCH 0/2] improve vmalloc allocation

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?

> It is fixed by second commit in this series. Please see more description in
> the commit message of the patch.

Bug fixes should go first and new functionality should be built on top.
A kernel crash sounds serious enough to have a fix marked for stable. If
the fix is too hard/complex then we might consider a revert of the
faulty commit.
> 
> 3) This one is related to PCPU allocator(see pcpu_alloc_test()). In that
> stress test case i see that SUnreclaim(/proc/meminfo) parameter gets increased,
> i.e. there is a memory leek somewhere in percpu allocator. It sounds like
> a memory that is allocated by pcpu_get_vm_areas() sometimes is not freed.
> Resulting in memory leaking or "Kernel panic":
> 
> ---[ end Kernel panic - not syncing: Out of memory and no killable processes...

It would be great to pin point this one down before the rework as well.

Thanks a lot!
-- 
Michal Hocko
SUSE Labs