linux-kernel - Re: [RFC PATCH 00/30] Code tagging framework and applications

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Date:   Mon, 5 Sep 2022 19:50:07 -0400
From:   Kent Overstreet <kent.overstreet@...ux.dev>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Suren Baghdasaryan <surenb@...gle.com>,
        Michal Hocko <mhocko@...e.com>, Mel Gorman <mgorman@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Davidlohr Bueso <dave@...olabs.net>,
        Matthew Wilcox <willy@...radead.org>,
        "Liam R. Howlett" <liam.howlett@...cle.com>,
        David Vernet <void@...ifault.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Peter Xu <peterx@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Jens Axboe <axboe@...nel.dk>, mcgrof@...nel.org,
        masahiroy@...nel.org, nathan@...nel.org, changbin.du@...el.com,
        ytcoode@...il.com, Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Benjamin Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Christopher Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, 42.hyeyoo@...il.com,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
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        Muchun Song <songmuchun@...edance.com>, arnd@...db.de,
        jbaron@...mai.com, David Rientjes <rientjes@...gle.com>,
        Minchan Kim <minchan@...gle.com>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        kernel-team <kernel-team@...roid.com>,
        linux-mm <linux-mm@...ck.org>, iommu@...ts.linux.dev,
        kasan-dev@...glegroups.com, io-uring@...r.kernel.org,
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        linux-bcache@...r.kernel.org, linux-modules@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 00/30] Code tagging framework and applications

On Mon, Sep 05, 2022 at 06:16:50PM -0400, Steven Rostedt wrote:
> On Mon, 5 Sep 2022 16:42:29 -0400
> Kent Overstreet <kent.overstreet@...ux.dev> wrote:
> 
> > > Haven't tried that yet but will do. Thanks for the reference code!  
> > 
> > Is it really worth the effort of benchmarking tracing API overhead here?
> > 
> > The main cost of a tracing based approach is going to to be the data structure
> > for remembering outstanding allocations so that free events can be matched to
> > the appropriate callsite. Regardless of whether it's done with BFP or by
> > attaching to the tracepoints directly, that's going to be the main overhead.
> 
> The point I was making here is that you do not need your own hooking
> mechanism. You can get the information directly by attaching to the
> tracepoint.
> 
> > > static void my_callback(void *data, unsigned long call_site,
> > >                         const void *ptr, struct kmem_cache *s,
> > >                         size_t bytes_req, size_t bytes_alloc,
> > >                         gfp_t gfp_flags)
> > > {
> > >         struct my_data_struct *my_data = data;
> > >
> > >         { do whatever }
> > > }
> 
> The "do whatever" is anything you want to do.
> 
> Or is the data structure you create with this approach going to be too much
> overhead? How hard is it for a hash or binary search lookup?

If you don't think it's hard, go ahead and show us.