linux-kernel - Re: [PATCH v2 14/23] mm/slab_common: print cache name in tracepoints

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Message-ID: <20220430140654.GB25819@ip-172-31-27-201.ap-northeast-1.compute.internal>
Date:   Sat, 30 Apr 2022 14:06:55 +0000
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Marco Elver <elver@...gle.com>,
        Matthew WilCox <willy@...radead.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 14/23] mm/slab_common: print cache name in tracepoints

On Fri, Apr 29, 2022 at 04:05:14PM +0200, Vlastimil Babka wrote:
> On 4/14/22 10:57, Hyeonggon Yoo wrote:
> > Print cache name in tracepoints. If there is no corresponding cache
> > (kmalloc in SLOB or kmalloc_large_node), use KMALLOC_{,LARGE_}NAME
> > macro.
> > 
> > Signed-off-by: Hyeonggon Yoo <42.hyeyoo@...il.com>
> 
> Regarding tracepoints, I'm not sure it's a good idea to unify kmalloc and
> kmem_cache_alloc. I think the common use case is to trace kmalloc as there
> are many different callers, and then I'm not interested in kmem_cache_alloc
> callers much.

Make sense.

> What I would suggest instead is:
> - drop the _node versions, add node to normal versions
> - drop the kmem_alloc EVENT_CLASS, as kmalloc is different enough from
> kmem_cache_alloc (see next points), define separately as TRACE_EVENT().
> - printing cache_name makes sense to add for kmem_cache_alloc (also allows
> filtering events) but not for kmalloc.
> - kmem_cache_alloc with name can then drop the bytes_req, bytes_alloc as
> they are fixed for given name (and can be read from slabinfo).

Those suggestions makes sense to me.
kmalloc and kmem_cache_alloc are a bit different.

> Not using a common tracepoint will prevent some later unifications/cleanup
> (patch 21?), but hopefully not too much?

In v2 unification of __kmalloc_node()/kfree() somewhat depends on unified tracepoint.
I'll try to unify them with this approach in v3.