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: <2cee98d1-bdaa-4252-a9a6-15b1bc864ba0@linux.dev>
Date: Fri, 27 Jun 2025 23:45:15 +0800
From: Lance Yang <lance.yang@...ux.dev>
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>, 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>,
 Lance Yang <ioworker0@...il.com>
Subject: Re: [PATCH v1 3/4] mm: split folio_pte_batch() into folio_pte_batch()
 and folio_pte_batch_ext()

On 2025/6/27 23:09, David Hildenbrand wrote:
> 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.

Right, that makes sense. No need to force "__always_inline" prematurely.