Re: [PATCH] trace-cmd: Try alternate path for message cache

[Tzvetomir Stoyanov <tz.stoyanov@gmail.com>]

On Mon, Apr 4, 2022 at 7:41 AM Tzvetomir Stoyanov <tz.stoyanov@gmail.com> wrote:
>
> On Sun, Apr 3, 2022 at 5:56 PM Joel Fernandes <joel@joelfernandes.org> wrote:
> >
> > On Fri, Apr 01, 2022 at 07:06:29PM -0400, Steven Rostedt wrote:
> > > On Fri, 1 Apr 2022 15:50:10 -0400
> > > Joel Fernandes <joel@joelfernandes.org> wrote:
> > >
> > > > export TRACECMD_TEMPDIR="/data"
> > > >
> > > > That’s fair. What about using memfd for this, do you feel that’s
> > > > reasonable? I have not yet measured how big this file gets but if it’s
> > > > small enough that might work too.
> > >
> > > Is this a separate question? That is, do you mean using the above
> > > environment variable *and* then use memfd?
> > >
> > > I believe that the cache is used for passing the compressed data from the
> > > guest to the host. I don't think it will be more than one compressed chunk.
> > >
> > > But Tzvetomir would know better.
> >
> > Hey Steve,
> > No its the same question. Instead of temp file, I was proposing in-memory
> > file using memfd_create(2), that way no hassle as long as the file is not too
> > huge.
> >
>
> Hi  Joel,
> That cache file is used for constructing the trace meta-data on the
> guest, before sending it to the host. Usually it is compressed, but it
> could be uncompressed in some cases (depending on the configuration) -
> and in that case it can grow up to a few megabytes. Using memfd is ok
> in most cases, but I'm wondering in the worst case - these few
> megabytes could be a problem, especially if the guest runs with a
> minimum amount of memory.
>

Can you check that file size on your Android setup with that command,
it will force to not use compression on the guest trace file:
   trace-cmd <host trace options> -A <guest> <guest trace options>
--file-version 7 --compression none

Thanks!

> > Also looks like my patch is incomplete anyway, I need to change
> > tracecmd_msg_handle_cache() as well.
> >
> > I'll try to write up a patch with memfd unless you guys disagree.
> >
> > Thanks,
> >
> > - Joel
> >
>
>
> --
> Tzvetomir (Ceco) Stoyanov
> VMware Open Source Technology Center



-- 
Tzvetomir (Ceco) Stoyanov
VMware Open Source Technology Center