From: Jiri Olsa <jolsa@redhat.com>
To: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Namhyung Kim <namhyung@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Michael Petlan <mpetlan@redhat.com>
Subject: Re: [PATCH 3/3] perf tools: Make 'struct map_shared' truly shared
Date: Mon, 14 Oct 2019 21:20:49 +0200 [thread overview]
Message-ID: <20191014192049.GB15890@krava> (raw)
In-Reply-To: <20191014031054.GJ9933@tassilo.jf.intel.com>
On Sun, Oct 13, 2019 at 08:10:54PM -0700, Andi Kleen wrote:
> On Sun, Oct 13, 2019 at 05:14:27PM +0200, Jiri Olsa wrote:
> > Andi reported that maps cloning is eating lot of memory and
> > it's probably unnecessary, because they keep the same data.
> >
> > Changing 'struct map_shared' to be a pointer inside 'struct map',
> > so it can be shared on fork. Changing the map__clone function to
> > actually share 'struct map_shared' for cloned maps.
> >
> > The 'struct map_shared' carries its own refcnt counter, which is
> > incremented when it's assigned to new 'struct map' and decremented
> > when 'struct map' gets deleted in map__delete (its refcnt is 0).
> >
> > This 'maps sharing' seems to save lot of heap for reports with
> > many forks/cloned mmaps (over 60% in example below).
>
> The one case I wasn't sure about is with JIT support. So if
> a map gets modified with fixup/start from /tmp/perf-%d
> in one process, would it impact the other too?
>
> We may need a COW operation for this (hopefully rare) case.
so the jitted mmaps are inserted into the data file
and processed during report where they can overload
existing maps - thats detected before addition in:
thread__insert_map
map_groups__fixup_overlappings
- which uses COW way -> map__clone(map, false);
to create new map
other fixups to maps are being done only for kernel maps,
where we dont have a problem, because there's only one copy
jirka
next prev parent reply other threads:[~2019-10-14 19:20 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-13 15:14 [PATCH 0/3] perf tools: Share struct map after clone Jiri Olsa
2019-10-13 15:14 ` [PATCH 1/3] perf tools: Allow to build with -ltcmalloc Jiri Olsa
2019-10-14 1:33 ` Andi Kleen
2019-10-14 14:01 ` Arnaldo Carvalho de Melo
2019-10-21 23:19 ` [tip: perf/core] " tip-bot2 for Jiri Olsa
2019-10-13 15:14 ` [PATCH 2/3] perf tools: Separate shareable part of 'struct map' into 'struct map_shared' Jiri Olsa
2019-10-13 15:14 ` [PATCH 3/3] perf tools: Make 'struct map_shared' truly shared Jiri Olsa
2019-10-14 3:10 ` Andi Kleen
2019-10-14 8:48 ` Jiri Olsa
2019-10-14 19:20 ` Jiri Olsa [this message]
2019-10-14 19:46 ` Andi Kleen
2019-10-14 20:40 ` Jiri Olsa
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