Re: [PATCH v2 3/4] mm: split folio_pte_batch() into folio_pte_batch() and folio_pte_batch_flags()

[Dev Jain <dev.jain@arm.com>]

On 02/07/25 4:19 pm, David Hildenbrand wrote:
> Many users (including upcoming ones) don't really need the flags etc,
> and can live with the possible overhead of a function call.
>
> So let's provide a basic, non-inlined folio_pte_batch(), to avoid code
> bloat while still providing a variant that optimizes out all flag
> checks at runtime. folio_pte_batch_flags() will get inlined into
> folio_pte_batch(), optimizing out any conditionals that depend on input
> flags.
>
> folio_pte_batch() will behave like folio_pte_batch_flags() when no
> flags are specified. It's okay to add new users of
> folio_pte_batch_flags(), but using folio_pte_batch() if applicable is
> preferred.
>
> So, before this change, folio_pte_batch() was inlined into the C file
> optimized by propagating constants within the resulting object file.
>
> With this change, we now also have a folio_pte_batch() that is
> optimized by propagating all constants. But instead of having one instance
> per object file, we have a single shared one.
>
> In zap_present_ptes(), where we care about performance, the compiler
> already seem to generate a call to a common inlined folio_pte_batch()
> variant, shared with fork() code. So calling the new non-inlined variant
> should not make a difference.
>
> While at it, drop the "addr" parameter that is unused.
>
> Suggested-by: Andrew Morton <akpm@linux-foundation.org>
> Link: https://lore.kernel.org/linux-mm/20250503182858.5a02729fcffd6d4723afcfc2@linux-foundation.org/
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>   

Having one place to share the inlined copy is amazing! In the near
future I will be doing some GNU toolchain work so hopefully I gain
knowledge on compiler stuff; it was fun reading the inlined
vs non-inlined discussion.

Reviewed-by: Dev Jain <dev.jain@arm.com>