linux-kernel - Re: [PATCH v1 4/4] mm: remove boolean output parameters from folio_pte_batch

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Message-ID: <62c00c9e-1ba4-46dd-a6e0-18e9eee7f93a@linux.dev>
Date: Fri, 27 Jun 2025 23:40:55 +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 4/4] mm: remove boolean output parameters from
 folio_pte_batch_ext()

On 2025/6/27 23:11, David Hildenbrand wrote:
> On 27.06.25 16:34, Lance Yang wrote:
>> On Fri, Jun 27, 2025 at 7:55 PM David Hildenbrand <david@...hat.com> 
>> wrote:
>>>
>>> Instead, let's just allow for specifying through flags whether we want
>>> to have bits merged into the original PTE.
>>>
>>> For the madvise() case, simplify by having only a single parameter for
>>> merging young+dirty. For madvise_cold_or_pageout_pte_range() merging the
>>> dirty bit is not required, but also not harmful. This code is not that
>>> performance critical after all to really force all micro-optimizations.
>>
>> IIRC, this work you've wanted to do for a long time - maybe even a 
>> year ago?
> 
> Heh, maybe, I don't remember.
> 
> For this user here, I realized that we might already check the existence 
> of any_dirty at runtime -- because the compiler will not necessarily 
> create two optimized functions.

Ah, I see! That's a very sharp observation about the compiler's behavior ;)

> 
> So we already have runtime checks ... instead of checking whether 
> any_dirty == NULL, we now simply do the merging (checking for 
> pte_young() instead) now.

Thanks for the lesson!
Lance