RE: [PATCH] mm/memremap: Mark folio_span_valid() as __maybe_unused

[Dan Williams <dan.j.williams@intel.com>]

Nathan Chancellor wrote:
> When building without CONFIG_DEBUG_VM, clang warns:
> 
>   mm/memremap.c:495:13: error: function 'folio_span_valid' is not needed and will not be emitted [-Werror,-Wunneeded-internal-declaration]
>   static bool folio_span_valid(struct dev_pagemap *pgmap, struct folio *folio,
>               ^
>   1 error generated.
> 
> folio_span_valid() is only used within a instance of VM_WARN_ON_ONCE(),
> which evaluates to BUILD_BUG_ON_INVALID() with CONFIG_DEBUG_VM=n, which
> ultimately resolves to sizeof(), which is fully resolved at compile
> time. Basically, the warning is flagging that folio_span_valid() is
> only used in a compile time context and will not be called at run time.
> 
> Since this is expected given the configuration, mark folio_span_valid()
> as __maybe_unused so that there is no warning.
> 
> Fixes: 07108d5bfeeb ("fsdax: introduce pgmap_request_folios()")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1739
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
> 
> I am aware the Fixes SHA is probably not stable but I figured I would
> include it anyways.

This fix looks good to me, but I assume commit-ids are not stable until
the patch moves from mm-unstable to mm-stable. Andrew, do I have that
right?