Re: [PATCH] mmap_lock: add tracepoints around lock acquisition

From: Axel Rasmussen <axelrasmussen@google.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Yafang Shao <laoar.shao@gmail.com>,
	Ingo Molnar <mingo@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	Michel Lespinasse <walken@google.com>,
	Daniel Jordan <daniel.m.jordan@oracle.com>,
	Davidlohr Bueso <dbueso@suse.de>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux MM <linux-mm@kvack.org>
Subject: Re: [PATCH] mmap_lock: add tracepoints around lock acquisition
Date: Wed, 23 Sep 2020 09:40:23 -0700	[thread overview]
Message-ID: <CAJHvVcgmJYZS=+g2_V7Bkx3fVGVZEytdpQDQgxu2nEe3qJh2OQ@mail.gmail.com> (raw)
In-Reply-To: <20200923120924.49638d90@oasis.local.home>

On Wed, Sep 23, 2020 at 9:09 AM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Wed, 23 Sep 2020 18:04:17 +0800
> Yafang Shao <laoar.shao@gmail.com> wrote:
>
> > > What you can do, and what we have done is the following:
> > >
> > > (see include/linux/page_ref.h)
> > >
> > >
> > > #ifdef CONFIG_TRACING
> > > extern struct tracepoint __tracepoint_mmap_lock_start_locking;
> > > extern struct tracepoint __tracepoint_mmap_lock_acquire_returned;
> > >
> > > #define mmap_lock_tracepoint_active(t) static_key_false(&(__tracepoint_mmap_lock_##t).key)
> > >
> > > #else
> > > #define mmap_lock_tracepoint_active(t) false
> > > #endif
> > >
> > > static inline void mmap_write_lock(struct mm_struct *mm)
> > > {
> > >         if (mmap_lock_tracepoint_active(start_locking))
> > >                 mmap_lock_start_trace_wrapper();
> > >         down_write(&mm->mmap_lock);
> > >         if (mmap_lock_tracepoint_active(acquire_returned))
> > >                 mmap_lock_acquire_trace_wrapper();
> > > }
> > >
> > >
> > > -- Steve
> >
> >
> > Great!
> >
> > Thanks Steve.
>
> If the above becomes useful, I may just add helper functions into a
> header file that you can include. Perhaps call it: tracepoint_active()
> and you need to pass in as an argument the name of the tracepoint.

Thanks for this suggestion Steven, it's working quite well.

I also have a very short patch to the tracing which allows plumbing
the string values through to "just work".

I plan to send out a v2 before the end of the week.

>
> -- Steve