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Date:   Wed, 23 Sep 2020 12:09:24 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Yafang Shao <laoar.shao@gmail.com>
Cc:     Axel Rasmussen <axelrasmussen@google.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
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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.

-- Steve