linux-kernel - Re: [PATCH v4 10/19] mm: memcg/slab: deprecate memory.kmem.slabinfo

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Message-ID: <20200527162808.GB396660@carbon.dhcp.thefacebook.com>
Date:   Wed, 27 May 2020 09:28:08 -0700
From:   Roman Gushchin <guro@...com>
To:     Vlastimil Babka <vbabka@...e.cz>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Shakeel Butt <shakeelb@...gle.com>, <linux-mm@...ck.org>,
        <kernel-team@...com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 10/19] mm: memcg/slab: deprecate memory.kmem.slabinfo

On Wed, May 27, 2020 at 05:54:50PM +0200, Vlastimil Babka wrote:
> On 5/26/20 11:42 PM, Roman Gushchin wrote:
> > Deprecate memory.kmem.slabinfo.
> > 
> > An empty file will be presented if corresponding config options are
> > enabled.
> > 
> > The interface is implementation dependent, isn't present in cgroup v2,
> > and is generally useful only for core mm debugging purposes. In other
> > words, it doesn't provide any value for the absolute majority of users.
> > 
> > A drgn-based replacement can be found in tools/cgroup/slabinfo.py .
> > It does support cgroup v1 and v2, mimics memory.kmem.slabinfo output
> > and also allows to get any additional information without a need
> > to recompile the kernel.
> > 
> > If a drgn-based solution is too slow for a task, a bpf-based tracing
> > tool can be used, which can easily keep track of all slab allocations
> > belonging to a memory cgroup.
> > 
> > Signed-off-by: Roman Gushchin <guro@...com>
> 
> Also there was a
> Acked-by: Johannes Weiner <hannes@...xchg.org>
> for this patch.
> And here's mine:
> Acked-by: Vlastimil Babka <vbabka@...e.cz>

Thanks!

> 
> Of course this depends on whether we break somebody's workflow and they complain.

We've discussed it a bit around RFC/v1. I hope nobody uses it for anything
except debug purposes, where dragon + bpf can be as good or better.

And actually it is what it is: there are no more per-memcg kmem caches,
so there is nothing to display.