linux-kernel - Re: [PATCH v2] tracing: Make percpu stack trace buffer invariant to PAGE

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Message-ID: <20241030171532.7ed01770@rorschach.local.home>
Date: Wed, 30 Oct 2024 17:15:32 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tracing: Make percpu stack trace buffer invariant to
 PAGE_SIZE

On Wed, 30 Oct 2024 08:50:16 +0000
Ryan Roberts <ryan.roberts@....com> wrote:

> On 21/10/2024 15:18, Ryan Roberts wrote:
> > Previously the size of "struct ftrace_stacks" depended upon PAGE_SIZE.
> > For the common 4K page size, on a 64-bit system, sizeof(struct
> > ftrace_stacks) was 32K. But for a 64K page size, sizeof(struct
> > ftrace_stacks) was 512K.
> > 
> > But ftrace stack usage requirements should be invariant to page size. So
> > let's redefine FTRACE_KSTACK_ENTRIES so that "struct ftrace_stacks" is
> > always sized at 32K for 64-bit and 16K for 32-bit.
> > 
> > As a side effect, it removes the PAGE_SIZE compile-time constant
> > assumption from this code, which is required to reach the goal of
> > boot-time page size selection.  
> 
> Just a polite bump on this... Does anyone have any comments?

No, it's in my queue. I've just been traveling.

-- Steve