linux-kernel - Re: [PATCH 0/3] mm: treewide: make get_free

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Message-ID: <85707316-3f2b-4e29-b821-a32f9097244e@kernel.org>
Date: Mon, 20 Oct 2025 09:06:48 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Matthew Wilcox <willy@...radead.org>, Mike Rapoport <rppt@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Brendan Jackman <jackmanb@...gle.com>, David Hildenbrand <david@...hat.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Johannes Weiner <hannes@...xchg.org>, Julia Lawall <Julia.Lawall@...ia.fr>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Michal Hocko
 <mhocko@...e.com>, Suren Baghdasaryan <surenb@...gle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Zi Yan <ziy@...dia.com>,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 0/3] mm: treewide: make get_free_pages() and return void *

On 20. 10. 25, 8:58, Jiri Slaby wrote:
> On 19. 10. 25, 2:30, Matthew Wilcox wrote:
>> On Sat, Oct 18, 2025 at 12:29:59PM +0300, Mike Rapoport wrote:
>>> Vast majority of allocations that use get_free_pages() and its 
>>> derivatives
>>> cast the returned unsigned long to a pointer and then cast it back to
>>> unsigned long when freeing the memory.
>>>
>>> These castings are useless and only obfuscate the code.
>>>
>>> Make get_free_pages() and friends return 'void *' and free_pages() 
>>> accept
>>> 'void *' as its address parameter.
>>
>> No.  Linus has rejected this change before.  I can't find it now, it was
>> a long time ago.  Most of them shouldn't be using get_free_pages() at
>> all, they should be using kmalloc().
> 
> I'd be interested in the refusal thread (what was the rejection exactly 
> about). In a need of whole pages, why would I want to alloc more for 
> metadata (using k*alloc)? Or what am I missing?

OK, AI yielded:
https://lkml.iu.edu/1512.2/03853.html
and an LWN summary:
https://lwn.net/Articles/669015/

> thanks,
-- 
js
suse labs