linux-kernel - Re: Re: [PATCH 3/3] mm: mmap_lock: add ip to mmap

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Date:   Mon, 2 Aug 2021 10:44:56 +0800
From:   Gang Li <ligang.bdlg@...edance.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Axel Rasmussen <axelrasmussen@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>
Subject: Re: Re: [PATCH 3/3] mm: mmap_lock: add ip to mmap_lock tracepoints

On 7/31/21 4:03 AM, Steven Rostedt wrote:
> Yes, synthetic events are just like normal events, and have triggers,
> stack traces, and do pretty much anything that another event can do.
> 
> I'm just finishing up a libtracfs called tracefs_sql() (hopefully
> posting it today), that allows you to create a synthetic event via an
> SQL statement. But I don't think this is what you are looking for.
> 
> What about using function tracing? Because the tracepoint is called
> from __mmap_lock* helper functions that function tracer can see, you
> can just do the following:
> 
>   # trace-cmd start -e mmap_lock -p function -l '__mmap_lock_*'
>   # trace-cmd show
> [..]
>         trace-cmd-1840    [006] ....   194.576801: __mmap_lock_do_trace_start_locking <-do_user_addr_fault
>         trace-cmd-1840    [006] ...1   194.576805: mmap_lock_start_locking: mm=000000006515cb1f memcg_path=/user.slice/user-0.slice/session-2.scope write=false
> 
>         trace-cmd-1840    [006] ....   194.576806: __mmap_lock_do_trace_acquire_returned <-do_user_addr_fault
>         trace-cmd-1840    [006] ...1   194.576807: mmap_lock_acquire_returned: mm=000000006515cb1f memcg_path=/user.slice/user-0.slice/session-2.scope write=false success=true
> 
>         trace-cmd-1840    [006] ....   194.576811: __mmap_lock_do_trace_released <-do_user_addr_fault
>         trace-cmd-1840    [006] ...1   194.576812: mmap_lock_released: mm=000000006515cb1f memcg_path=/user.slice/user-0.slice/session-2.scope write=false
> 
>         trace-cmd-1840    [006] ....   194.576815: __mmap_lock_do_trace_start_locking <-do_user_addr_fault
>         trace-cmd-1840    [006] ...1   194.576816: mmap_lock_start_locking: mm=000000006515cb1f memcg_path=/user.slice/user-0.slice/session-2.scope write=false
> 
>         trace-cmd-1840    [006] ....   194.576816: __mmap_lock_do_trace_acquire_returned <-do_user_addr_fault
>         trace-cmd-1840    [006] ...1   194.576817: mmap_lock_acquire_returned: mm=000000006515cb1f memcg_path=/user.slice/user-0.slice/session-2.scope write=false success=true
> 
>         trace-cmd-1840    [006] ....   194.576820: __mmap_lock_do_trace_released <-do_user_addr_fault
>         trace-cmd-1840    [006] ...1   194.576821: mmap_lock_released: mm=000000006515cb1f memcg_path=/user.slice/user-0.slice/session-2.scope write=false
> 
> 
> This looks exactly like the robots you are looking for.
> 
> -- Steve
> 

I think this is exactly what I am looking for.
Thanks!