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Date: Thu, 19 Jun 2025 09:56:11 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
	bpf@vger.kernel.org, x86@kernel.org,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Josh Poimboeuf <jpoimboe@kernel.org>,
	Ingo Molnar <mingo@kernel.org>, Jiri Olsa <jolsa@kernel.org>,
	Namhyung Kim <namhyung@kernel.org>,
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	Andrii Nakryiko <andrii@kernel.org>,
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	"Jose E. Marchesi" <jemarch@gnu.org>,
	Beau Belgrave <beaub@linux.microsoft.com>,
	Jens Remus <jremus@linux.ibm.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v10 05/14] unwind_user/deferred: Add unwind cache
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On Wed, Jun 18, 2025 at 11:33:59AM -0400, Steven Rostedt wrote:
> On Wed, 18 Jun 2025 16:13:45 +0200
> Peter Zijlstra <peterz@infradead.org> wrote:

> > > +		info->cache = kzalloc(struct_size(cache, entries, UNWIND_MAX_ENTRIES),
> > > +				      GFP_KERNEL);  
> > 
> > And now you're one 'long' larger than a page. Surely that's a crap size
> > for an allocator?
> 
> Bah, Ingo suggested to put the counter in the allocation and I didn't think
> about the size going over the page. Good catch!
> 
> Since it can make one per task, it may be good to make this into a
> kmemcache.

Well, the trivial solution is to make it 511 and call it a day. Don't
make things complicated if you don't have to.