linux-kernel - Re: [PATCH 00/16] The new slab memory controller

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Date:   Tue, 10 Dec 2019 11:53:08 +0530
From:   Bharata B Rao <bharata@...ux.ibm.com>
To:     Roman Gushchin <guro@...com>
Cc:     "mhocko@...nel.org" <mhocko@...nel.org>,
        "hannes@...xchg.org" <hannes@...xchg.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        "shakeelb@...gle.com" <shakeelb@...gle.com>,
        "vdavydov.dev@...il.com" <vdavydov.dev@...il.com>,
        "longman@...hat.com" <longman@...hat.com>
Subject: Re: [PATCH 00/16] The new slab memory controller

On Mon, Dec 09, 2019 at 06:04:22PM +0000, Roman Gushchin wrote:
> On Mon, Dec 09, 2019 at 05:26:49PM +0530, Bharata B Rao wrote:
> > On Mon, Dec 09, 2019 at 02:47:52PM +0530, Bharata B Rao wrote:
> Hello, Bharata!
> 
> Thank you very much for the report and the patch, it's a good catch,
> and the code looks good to me. I'll include the fix into the next
> version of the patchset (I can't keep it as a separate fix due to massive
> renamings/rewrites).

Sure, but please note that I did post only the core change without
the associated header includes etc, where I took some short cuts.

> 
> > 
> > But that still doesn't explain why we don't hit this problem on x86.
> 
> On x86 (and arm64) we're using vmap-based stacks, so the underlying memory is
> allocated directly by the page allocator, bypassing the slab allocator.
> It depends on CONFIG_VMAP_STACK.

I turned off CONFIG_VMAP_STACK on x86, but still don't hit any
problems.

$ grep VMAP .config
CONFIG_HAVE_ARCH_HUGE_VMAP=y
CONFIG_HAVE_ARCH_VMAP_STACK=y
# CONFIG_VMAP_STACK is not set

May be something else prevents this particular crash on x86?

> 
> Btw, thank you for looking into the patchset and trying it on powerpc.
> Would you mind to share some results?

Sure, I will get back with more results, but initial numbers when running
a small alpine docker image look promising.

With slab patches
# docker stats --no-stream
CONTAINER ID        NAME                CPU %               MEM USAGE / LIMIT   MEM %               NET I/O             BLOCK I/O           PIDS
24bc99d94d91        sleek               0.00%               1MiB / 25MiB        4.00%               1.81kB / 0B         0B / 0B             0

Without slab patches
# docker stats --no-stream
CONTAINER ID        NAME                CPU %               MEM USAGE / LIMIT   MEM %               NET I/O             BLOCK I/O           PIDS
52382f8aaa13        sleek               0.00%               8.688MiB / 25MiB    34.75%              1.53kB / 0B         0B / 0B             0

So that's an improvement of MEM USAGE from 8.688MiB to 1MiB. Note that this
docker container isn't doing anything useful and hence the numbers
aren't representative of any workload.

Regards,
Bharata.