linux-kernel - Re: [RFC PATCH v1 18/57] trace: Remove PAGE

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Message-ID: <20241018112411.6311a9e9@gandalf.local.home>
Date: Fri, 18 Oct 2024 11:24:11 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Anshuman Khandual
 <anshuman.khandual@....com>, Ard Biesheuvel <ardb@...nel.org>, Catalin
 Marinas <catalin.marinas@....com>, David Hildenbrand <david@...hat.com>,
 Greg Marsden <greg.marsden@...cle.com>, Ivan Ivanov <ivan.ivanov@...e.com>,
 Kalesh Singh <kaleshsingh@...gle.com>, Marc Zyngier <maz@...nel.org>, Mark
 Rutland <mark.rutland@....com>, Masami Hiramatsu <mhiramat@...nel.org>,
 Matthias Brugger <mbrugger@...e.com>, Miroslav Benes <mbenes@...e.cz>, Will
 Deacon <will@...nel.org>, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 18/57] trace: Remove PAGE_SIZE compile-time
 constant assumption

On Tue, 15 Oct 2024 12:09:38 +0100
Ryan Roberts <ryan.roberts@....com> wrote:

> > 
> > Not to mention, when function graph tracing is enabled, this gets triggered
> > for *every* function call! So I do not want any runtime test done. Every
> > nanosecond counts in this code path.
> > 
> > If anything, this needs to be moved to initialization and checked once, if
> > it fails, gives a WARN_ON() and disables function graph tracing.  
> 
> I'm hoping my suggestion above to decouple SHADOW_STACK_SIZE from PAGE_SIZE is
> acceptable and simpler? If not, happy to do as you suggest here.

Yeah, I think we can do that. In fact, I'm thinking it should turn into a
kmem_cache item that doesn't have to be a power of two (but must be evenly
divisible by the size of long).

I'll write up a patch.

-- Steve