linux-kernel - Re: [PATCH RESEND] perf inject --jit: Remove //anon mmap events

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Message-ID: <20191019174900.GC12782@krava>
Date:   Sat, 19 Oct 2019 19:49:00 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Steve MacLean <steve.maclean@...ux.microsoft.com>
Cc:     Steve MacLean <Steve.MacLean@...rosoft.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Stephane Eranian <eranian@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND] perf inject --jit: Remove //anon mmap events

On Thu, Oct 17, 2019 at 11:23:20AM -0700, Steve MacLean wrote:
> From: Steve MacLean <Steve.MacLean@...rosoft.com>
> 
> While a JIT is jitting code it will eventually need to commit more pages and
> change these pages to executable permissions.
> 
> Typically the JIT will want these colocated to minimize branch displacements.
> 
> The kernel will coalesce these anonymous mapping with identical permissions
> before sending an MMAP event for the new pages. This means the mmap event for
> the new pages will include the older pages.
> 
> These anonymous mmap events will obscure the jitdump injected pseudo events.
> This means that the jitdump generated symbols, machine code, debugging info,
> and unwind info will no longer be used.
> 
> Observations:
> 
> When a process emits a jit dump marker and a jitdump file, the perf-xxx.map
> file represents inferior information which has been superceded by the
> jitdump jit-xxx.dump file.
> 
> Further the '//anon*' mmap events are only required for the legacy
> perf-xxx.map mapping.
> 
> Summary:
> 
> Add rbtree to track which pids have sucessfully injected a jitdump file.
> 
> During "perf inject --jit", discard "//anon*" mmap events for any pid which
> has sucessfully processed a jitdump file.
> 
> Committer testing:
> 
> // jitdump case
> perf record <app with jitdump>
> perf inject --jit --input perf.data --output perfjit.data
> 
> // verify mmap "//anon" events present initially
> perf script --input perf.data --show-mmap-events | grep '//anon'
> // verify mmap "//anon" events removed
> perf script --input perfjit.data --show-mmap-events | grep '//anon'
> 
> // no jitdump case
> perf record <app without jitdump>
> perf inject --jit --input perf.data --output perfjit.data
> 
> // verify mmap "//anon" events present initially
> perf script --input perf.data --show-mmap-events | grep '//anon'
> // verify mmap "//anon" events not removed
> perf script --input perfjit.data --show-mmap-events | grep '//anon'
> 
> Repro:
> 
> This issue was discovered while testing the initial CoreCLR jitdump
> implementation. https://github.com/dotnet/coreclr/pull/26897.

I posted some questions for previous version in here,
but can't find answers:
  https://lore.kernel.org/lkml/20191003105716.GB23291@krava/

thanks,
jirka