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

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Message-ID: <42BA6F99-8DCD-41EF-87E9-A538FACD15D4@nvidia.com>
Date: Wed, 02 Jul 2025 10:25:52 -0400
From: Zi Yan <ziy@...dia.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
 Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>,
 Michal Hocko <mhocko@...e.com>, Matthew Brost <matthew.brost@...el.com>,
 Joshua Hahn <joshua.hahnjy@...il.com>, Rakie Kim <rakie.kim@...com>,
 Byungchul Park <byungchul@...com>, Gregory Price <gourry@...rry.net>,
 Ying Huang <ying.huang@...ux.alibaba.com>,
 Alistair Popple <apopple@...dia.com>, Pedro Falcato <pfalcato@...e.de>,
 Rik van Riel <riel@...riel.com>, Harry Yoo <harry.yoo@...cle.com>,
 Lance Yang <ioworker0@...il.com>, Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH v2 3/4] mm: split folio_pte_batch() into folio_pte_batch()
 and folio_pte_batch_flags()

On 2 Jul 2025, at 6:49, 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@...ux-foundation.org>
> Link: https://lore.kernel.org/linux-mm/20250503182858.5a02729fcffd6d4723afcfc2@linux-foundation.org/
> Reviewed-by: Oscar Salvador <osalvador@...e.de>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  mm/internal.h  | 11 ++++++++---
>  mm/madvise.c   |  4 ++--
>  mm/memory.c    |  8 +++-----
>  mm/mempolicy.c |  3 +--
>  mm/mlock.c     |  3 +--
>  mm/mremap.c    |  3 +--
>  mm/rmap.c      |  3 +--
>  mm/util.c      | 29 +++++++++++++++++++++++++++++
>  8 files changed, 46 insertions(+), 18 deletions(-)
>
Reviewed-by: Zi Yan <ziy@...dia.com>

Best Regards,
Yan, Zi