Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20201001065104.apevlkqrs6nid3r5@hp-nas.internet>
In-Reply-To: <20201001065104.apevlkqrs6nid3r5@hp-nas.internet>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 1 Oct 2020 12:19:57 -0700
Message-ID: <CAHk-=wixd9kUup4o1d1y9Wg9WoRt6_mN7kM5sPX=_nrgrkZzFg@mail.gmail.com>
Subject: Re: Linux 5.9-rc7 / VmallocTotal wrongly reported
To:     Bastian Bittorf <bb@npl.de>, Vlastimil Babka <vbabka@suse.cz>,
        Roman Gushchin <guro@fb.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Adding Vlastimil, Roman and the kernel mailing list to the cc.

Vlastimil, Roman - this looks like a slab regression. And while others
have touched slab in this merge window, you guys did so more than
most.. Comments?

On Wed, Sep 30, 2020 at 11:55 PM Bastian Bittorf <bb@npl.de> wrote:
>
> Since 5.9-rc1 i can see false values, booting with qemu (128mb RAM):
>
> / # free
>               total        used        free      shared  buff/cache available
> Mem:         122176 18014398506028288      114848           0 3461024     3568096

that looks like a negative 64-bit number shifted down by 10 bits (bytes -> kB).

> / # cat /proc/meminfo | grep ^V
> VmallocTotal:   34359738367 kB

.. but this part is normal. VMALLOC_TOTAL is the VM space for vmalloc
areas, and it's large on a 64-bit machine.

And afaik, it hasn't changed in a long time.

So I think there's something else confusing 'free'.

I think it's this:

> / # cat /proc/meminfo
> MemAvailable:    3617184 kB
..
> Slab:           10321920 kB
> SReclaimable:    3506176 kB
> SUnreclaim:      6815744 kB

because those slab reclaimable/unreclaimable numbers look completely
bogus. You have more unreclaimable slab space than you have memory.

Hmm. I'm not seeing anything similar. And your config looks sane, with
the main difference I see wrt SLAB being that you have

# CONFIG_SLAB_MERGE_DEFAULT is not set

but there's nothing wrong with that either.

It would be lovely if you could bisect it, but maybe Vlastimil or
Roman will go "Ahh, obviously.."

                 Linus