linux-kernel - Re: [PATCH v10 05/14] unwind_user/deferred: Add unwind cache

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Message-ID: <88E4D247-84F1-41A8-AA64-0E1390F41B1E@goodmis.org>
Date: Thu, 19 Jun 2025 05:12:18 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Peter Zijlstra <peterz@...radead.org>
CC: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 bpf@...r.kernel.org, x86@...nel.org, Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Josh Poimboeuf <jpoimboe@...nel.org>, Ingo Molnar <mingo@...nel.org>,
 Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, Andrii Nakryiko <andrii@...nel.org>,
 Indu Bhagat <indu.bhagat@...cle.com>, "Jose E. Marchesi" <jemarch@....org>,
 Beau Belgrave <beaub@...ux.microsoft.com>, Jens Remus <jremus@...ux.ibm.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v10 05/14] unwind_user/deferred: Add unwind cache

On June 19, 2025 5:04:36 AM EDT, Peter Zijlstra <peterz@...radead.org> wrote:
>On Thu, Jun 19, 2025 at 04:47:14AM -0400, Steven Rostedt wrote:
>> On Thu, 19 Jun 2025 09:56:11 +0200
>> Peter Zijlstra <peterz@...radead.org> wrote:
>> 
>> > 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.
>> 
>> I don't know if this is more complicated, but it should make it fit
>> nicely in a page:
>> 
>>   /* Make the cache fit in a page */
>>   #define UNWIND_MAX_ENTRIES                                      \
>>         ((PAGE_SIZE - sizeof(struct unwind_cache)) / sizeof(long))
>
>Right, that's the fancy way of spelling 511 :-) Except on 32bit, where
>it now spells 1023 instead.
>
>Did you want that bitness difference?
>
>Also, you ready for some *reaaally* big numbers on Power/ARM with 64K
>pages? :-)

Bah, yeah, I need to use a size and not just PAGE_SIZE.

 Thanks,

-- Steve