linux-kernel - Re: [PATCH] mm: mmap_lock: optimize mmap

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Message-ID: <i3joc4vme76imq2etk7gjfntsy2z5l5niyqobeun5e7m6jh4yi@adwzrxbvuc6l>
Date: Sat, 23 Nov 2024 13:35:24 -0800
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Matthew Wilcox <willy@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Muchun Song <muchun.song@...ux.dev>, 
	Vlastimil Babka <vbabka@...e.cz>, Axel Rasmussen <axelrasmussen@...gle.com>, 
	Steven Rostedt <rostedt@...dmis.org>, Suren Baghdasaryan <surenb@...gle.com>, linux-mm@...ck.org, 
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH] mm: mmap_lock: optimize mmap_lock tracepoints

On Sat, Nov 23, 2024 at 05:01:57PM +0000, Matthew Wilcox wrote:
> On Fri, Nov 22, 2024 at 10:09:39PM -0800, Shakeel Butt wrote:
> >  	TP_printk(
> > -		"mm=%p memcg_path=%s write=%s",
> > -		__entry->mm,
> > -		__get_str(memcg_path),
> > +		"mm=%p memcg_id=%llu write=%s",
> > +		__entry->mm, __entry->memcg_id,
> >  		__entry->write ? "true" : "false"
> 
> Is it actually useful to print out the (hashed) pointer of the mm?
> Wouldn't the PID be more useful so you could actually associate it with
> a task?
> 

For our usecase i.e. bpftrace, we don't really care about these prints
as we can directly access the arguments like mm in bpftrace. I wonder if
others are using this hased pointer in some other way. I don't mind
chaning it but I think that would be a separate patch.