Re: [PATCH] perf tool: add skip_not_exec_file_map_events option

[zhizhi xu]

On Thu, 18 Aug 2022 at 23:00, Ian Rogers <irogers@xxxxxxxxxx> wrote:
>
> On Wed, Aug 17, 2022 at 8:24 PM lika you <tcwzxx@xxxxxxxxx> wrote:
> >
> > I'm so sorry for forgetting to reply to all. Here is the reply again.
> >
> > Thanks for the reply.
> >
> > The background is we have two types of tasks running on the same host.The high
> > priority one which is CPU overhead and the low priority which is IO overhead.
> > The high priority task has mmap many files as shared memory. The low priority
> > task may load multi TB data from SSD at once time which will cause the high
> > priority task file page cache to be swapped out. So we mmap all files with the
> > PROT_EXEC flag to prevent hot page cache to be swapped out. That cause
> > too many executable memory regions without symbols on it.
> >
> > The trick is implementate here.
> > https://github.com/torvalds/linux/blob/master/mm/vmscan.c#L2572
> >
> > Thanks again
>
> Thanks. So you are making data pages executable for the sake of
> getting "better chances to stay in memory under moderate memory
> pressure." Having lots of executable pages in your program isn't
> great, I'm reminded of efforts to stop stacks from being executable.
> This also feels like a case where madvise should be being used, for
> example, the MADV_WILLNEED option. Given this, I'm not sure supporting
> this case in the perf tool makes sense.
>
> > On Thu, 18 Aug 2022 at 02:13, Ian Rogers <irogers@xxxxxxxxxx> wrote:
> > >
> > > On Wed, Aug 17, 2022 at 6:43 AM tcwzxx <tcwzxx@xxxxxxxxx> wrote:
> > > >
> > > > When generate the flame graph, the perf-script subcommand will
> > > > process all mmap event and add them to the rbtree. The 240,000
> > > > mmap region takes about 5 minutes, which is not useful for flame
> > > > graph. So add the skip-not-exec-file-map-events option to skip
> > > > not PROT_EXEC flag memory regions.
> > > >
> > > > Signed-off-by: tcwzxx <tcwzxx@xxxxxxxxx>
> > >
> > > Could you provide more context? A reproduction?
> > >
> > > When we synthesize mmap events we drop non-executable pages:
> > > https://github.com/torvalds/linux/blob/master/tools/perf/util/synthetic-events.c#L466
> > >
> > > Similarly in the kernel for the "dummy" event:
> > > https://github.com/torvalds/linux/blob/master/kernel/events/core.c#L8258
> > >
> > > Thanks,
> > > Ian
> > >
> > > > ---
> > > >  tools/perf/builtin-report.c | 2 ++
> > > >  tools/perf/builtin-script.c | 3 +++
> > > >  tools/perf/util/machine.c   | 3 +++
> > > >  tools/perf/util/map.c       | 5 +++++
> > > >  tools/perf/util/map.h       | 2 ++
> > > >  5 files changed, 15 insertions(+)
> > > >
> > > > diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
> > > > index 91ed41cc7d88..c28eb9450a66 100644
> > > > --- a/tools/perf/builtin-report.c
> > > > +++ b/tools/perf/builtin-report.c
> > > > @@ -1364,6 +1364,8 @@ int cmd_report(int argc, const char **argv)
> > > >                     "Disable raw trace ordering"),
> > > >         OPT_BOOLEAN(0, "skip-empty", &report.skip_empty,
> > > >                     "Do not display empty (or dummy) events in the output"),
> > > > +       OPT_BOOLEAN(0, "skip-not-exec-file-map_events", &skip_not_exec_file_map_events,
> > > > +                   "skip not exec map events"),
> > > >         OPT_END()
> > > >         };
> > > >         struct perf_data data = {
> > > > diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
> > > > index 13580a9c50b8..e3f4e5e654c9 100644
> > > > --- a/tools/perf/builtin-script.c
> > > > +++ b/tools/perf/builtin-script.c
> > > > @@ -32,6 +32,7 @@
> > > >  #include "util/time-utils.h"
> > > >  #include "util/path.h"
> > > >  #include "util/event.h"
> > > > +#include "util/map.h"
> > > >  #include "ui/ui.h"
> > > >  #include "print_binary.h"
> > > >  #include "archinsn.h"
> > > > @@ -3936,6 +3937,8 @@ int cmd_script(int argc, const char **argv)
> > > >                     "Guest code can be found in hypervisor process"),
> > > >         OPT_BOOLEAN('\0', "stitch-lbr", &script.stitch_lbr,
> > > >                     "Enable LBR callgraph stitching approach"),
> > > > +       OPT_BOOLEAN(0, "skip-not-exec-map_events", &skip_not_exec_file_map_events,
> > > > +                   "skip not exec map events"),
> > > >         OPTS_EVSWITCH(&script.evswitch),
> > > >         OPT_END()
> > > >         };
> > > > diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> > > > index 2a16cae28407..21dde9f9935c 100644
> > > > --- a/tools/perf/util/machine.c
> > > > +++ b/tools/perf/util/machine.c
> > > > @@ -1904,6 +1904,9 @@ int machine__process_mmap2_event(struct machine *machine,
> > > >         if (thread == NULL)
> > > >                 goto out_problem;
> > > >
> > > > +       if (skip_not_exec_file_map_events && !(event->mmap2.prot & PROT_EXEC))
> > > > +               goto out_problem;
>
> Do you mean to drop all executable pages with the flag here or just
> those with the DSO__TYPE_UNKNOWN (as below)? It reads that all
> executable pages will be dropped.
>
> Thanks,
> Ian
>

Thank you for your advice.
I mean remove non-executable pages and non-ELF files

!(event->mmap2.prot & PROT_EXEC)

Thanks

> > > > +
> > > >         map = map__new(machine, event->mmap2.start,
> > > >                         event->mmap2.len, event->mmap2.pgoff,
> > > >                         &dso_id, event->mmap2.prot,
> > > > diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
> > > > index e0aa4a254583..2b51ca012c91 100644
> > > > --- a/tools/perf/util/map.c
> > > > +++ b/tools/perf/util/map.c
> > > > @@ -16,6 +16,8 @@
> > > >  #include "thread.h"
> > > >  #include "vdso.h"
> > > >
> > > > +bool skip_not_exec_file_map_events;
> > > > +
> > > >  static inline int is_android_lib(const char *filename)
> > > >  {
> > > >         return strstarts(filename, "/data/app-lib/") ||
> > > > @@ -168,6 +170,9 @@ struct map *map__new(struct machine *machine, u64 start, u64 len,
> > > >                 if (dso == NULL)
> > > >                         goto out_delete;
> > > >
> > > > +               if (skip_not_exec_file_map_events && dso__type(dso, machine) == DSO__TYPE_UNKNOWN)
> > > > +                       goto out_delete;
> > > > +
> > > >                 map__init(map, start, start + len, pgoff, dso);
> > > >
> > > >                 if (anon || no_dso) {
> > > > diff --git a/tools/perf/util/map.h b/tools/perf/util/map.h
> > > > index 3dcfe06db6b3..67b0e0f9f0ae 100644
> > > > --- a/tools/perf/util/map.h
> > > > +++ b/tools/perf/util/map.h
> > > > @@ -11,6 +11,8 @@
> > > >  #include <stdbool.h>
> > > >  #include <linux/types.h>
> > > >
> > > > +extern bool skip_not_exec_file_map_events;
> > > > +
> > > >  struct dso;
> > > >  struct maps;
> > > >  struct machine;
> > > > --
> > > > 2.34.1
> > > >