Re: [linux-next:master 9995/11651] fs/buffer.c:2254:5: warning: stack frame size (2144) exceeds limit (1024) in 'block_read_full_folio'

From: Matthew Wilcox <willy@infradead.org>
To: Nathan Chancellor <nathan@kernel.org>
Cc: Brian Cain <bcain@quicinc.com>, kernel test robot <lkp@intel.com>,
	llvm@lists.linux.dev, kbuild-all@lists.01.org,
	Linux Memory Management List <linux-mm@kvack.org>,
	linux-hexagon@vger.kernel.org
Subject: Re: [linux-next:master 9995/11651] fs/buffer.c:2254:5: warning: stack frame size (2144) exceeds limit (1024) in 'block_read_full_folio'
Date: Sun, 15 May 2022 01:30:52 +0100	[thread overview]
Message-ID: <YoBJvJ9pVPtiRbUo@casper.infradead.org> (raw)
In-Reply-To: <YoAlvnyjEbYV4T1L@dev-arch.thelio-3990X>

On Sat, May 14, 2022 at 02:57:18PM -0700, Nathan Chancellor wrote:
> On Sat, May 14, 2022 at 05:28:33PM +0100, Matthew Wilcox wrote:
> > On Sun, May 15, 2022 at 12:23:46AM +0800, kernel test robot wrote:
> > > commit: 2c69e2057962b6bd76d72446453862eb59325b49 [9995/11651] fs: Convert block_read_full_page() to block_read_full_folio()
> > > config: hexagon-randconfig-r041-20220513 (https://download.01.org/0day-ci/archive/20220515/202205150051.3RzuooAG-lkp@intel.com/config)
> > > compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project 38189438b69ca27b4c6ce707c52dbd217583d046)
> > ...
> > > All warnings (new ones prefixed by >>):
> > > 
> > > >> fs/buffer.c:2254:5: warning: stack frame size (2144) exceeds limit (1024) in 'block_read_full_folio' [-Wframe-larger-than]
> > >    int block_read_full_folio(struct folio *folio, get_block_t *get_block)
> > >        ^
> > >    1 warning generated.
> > 
> > Now show the warnings that were removed.  This patch renames the
> > function, and I bet there was a similar warning before this patch.
> > 
> > But basically, I don't care about stack usage on hexagon with clang.
> > AIUI, it's a known bug.
> 
> For what it's worth, it seems like this is just 256K pages being 256K
> pages... MAX_BUF_PER_PAGE is PAGE_SIZE / 512 so *arr is 2048 bytes big
> in this configuration. You'd see a similar warning with PowerPC but that
> configuration is non-standard:

Ahh!  Yes, I'd forgotten that Hexagon has that crazy config option.
I think I can get rid of that enormous array of pointers, it just wasn't
a high priority for me.

> fs/buffer.c: In function ‘block_read_full_page’:
> fs/buffer.c:2337:1: warning: the frame size of 2064 bytes is larger than 1024 bytes [-Wframe-larger-than=]
>  2337 | }
>       | ^
> 
> It would be nice if the Intel folks could look at recognizing a function
> rename so that you are not bothered by reports like this.
> 
> As a side note... Brian, is there any reason for 256K pages to exist for
> Hexagon? This has been an option since Hexagon's introduction but is it
> actually used? 4K pages is the default and the help text says "use with
> caution". Perhaps the choice should be turned off altogether for
> CONFIG_COMPILE_TEST so that we cannot select this configuration and
> bother developers with these reports.
> 
> Cheers,
> Nathan