linux-kernel - Re: [PATCH v1 3/4] mm: split folio_pte_batch() into folio_pte_batch() and folio_pte_batch

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Message-ID: <9eb26777-cdfd-49df-9e1f-e326454ab477@redhat.com>
Date: Fri, 27 Jun 2025 17:09:04 +0200
From: David Hildenbrand <david@...hat.com>
To: Lance Yang <ioworker0@...il.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>, Zi Yan <ziy@...dia.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>
Subject: Re: [PATCH v1 3/4] mm: split folio_pte_batch() into folio_pte_batch()
 and folio_pte_batch_ext()

On 27.06.25 16:19, Lance Yang wrote:
> On Fri, Jun 27, 2025 at 7:55 PM David Hildenbrand <david@...hat.com> wrote:
>>
>> Many users (including upcoming ones) don't really need the flags etc,
>> and can live with a function call.
>>
>> So let's provide a basic, non-inlined folio_pte_batch().
>>
>> 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.
> 
> It's always an interesting dance with the compiler when it comes to inlining,
> isn't it? We want the speed of 'inline' for critical paths, but also a compact
> binary for the common case ...
> 
> This split is a nice solution to the classic 'inline' vs. code size dilemma ;p

Yeah, in particular when we primarily care about optimizing out all the 
unnecessary checks inside the function, not necessarily also inlining 
the function call itself.

If we ever realize we absolute must inline it into a caller, we could 
turn folio_pte_batch_ext() into an "__always_inline", but for now it 
does not seem like this is really required from my experiments.

-- 
Cheers,

David / dhildenb