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Date: Fri, 18 Oct 2024 11:24:11 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Ryan Roberts <ryan.roberts@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Anshuman Khandual
 <anshuman.khandual@arm.com>, Ard Biesheuvel <ardb@kernel.org>, Catalin
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 Deacon <will@kernel.org>, linux-arm-kernel@lists.infradead.org,
 linux-kernel@vger.kernel.org, linux-mm@kvack.org,
 linux-trace-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v1 18/57] trace: Remove PAGE_SIZE compile-time
 constant assumption
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On Tue, 15 Oct 2024 12:09:38 +0100
Ryan Roberts <ryan.roberts@arm.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