linux-kernel - Re: [PATCH v1 0/2] Free contiguous order-0 pages efficiently

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Message-ID: <acd0b9ab-9b7c-42b9-91a9-7fc85140b6ca@arm.com>
Date: Mon, 5 Jan 2026 16:41:58 +0000
From: Ryan Roberts <ryan.roberts@....com>
To: Zi Yan <ziy@...dia.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...nel.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Brendan Jackman <jackmanb@...gle.com>, Johannes Weiner <hannes@...xchg.org>,
 Uladzislau Rezki <urezki@...il.com>,
 "Vishal Moola (Oracle)" <vishal.moola@...il.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: Re: [PATCH v1 0/2] Free contiguous order-0 pages efficiently

On 05/01/2026 16:36, Zi Yan wrote:
> On 5 Jan 2026, at 11:17, Ryan Roberts wrote:
> 
>> Hi All,
>>
>> A recent change to vmalloc caused some performance benchmark regressions (see
>> [1]). I'm attempting to fix that (and at the same time signficantly improve
>> beyond the baseline) by freeing a contiguous set of order-0 pages as a batch.
>>
>> At the same time I observed that free_contig_range() was essentially doing the
>> same thing as vfree() so I've fixed it there too.
>>
>> I think I've convinced myself that free_pages_prepare() per order-0 page
>> followed by a single free_frozen_page_commit() or free_one_page() for the high
>> order block is safe/correct, but would be good if a page_alloc expert can
>> confirm!
>>
>> Applies against today's mm-unstable (344d3580dacd). All mm selftests run and
>> pass.
> 
> Kefeng has a series on using frozen pages for alloc_contig*() in mm-new
> and touches free_contig_range() as well. You might want to rebase on top
> of that.
> 
> I like your approach of freeing multiple order-0 pages as a batch, since
> they are essentially a non-compound high order page. I also pointed out
> a similar optimization when reviewing Kefeng’s patchset[1] (see my comment
> on __free_contig_frozen_range()).
> 
> In terms of rebase, there should be minor for free_contig_range(). In addition,
> maybe your free_prepared_contig_range() can replace __free_contig_frozen_range()
> in Kefeng’s version to improve performance for both code paths.

OK, great! I'll hold off on the rebase until I get some code review feedback on
this version (I'd like to hear someone agree that what I'm doing is actually
sound!). Assuming feedback is positive, I'll rebase v2 onto mm-new and look at
the extra optimization opportunites as you suggest.

Thanks,
Ryan

> 
> I will take a look at the patches. Thanks.
> 
> [1] https://lore.kernel.org/linux-mm/D90F7769-F3A8-4234-A9CE-F97BC48CCACE@nvidia.com/
> 
>>
>> Thanks,
>> Ryan
>>
>> Ryan Roberts (2):
>>   mm/page_alloc: Optimize free_contig_range()
>>   vmalloc: Optimize vfree
>>
>>  include/linux/gfp.h |   1 +
>>  mm/page_alloc.c     | 116 +++++++++++++++++++++++++++++++++++++++-----
>>  mm/vmalloc.c        |  29 +++++++----
>>  3 files changed, 125 insertions(+), 21 deletions(-)
>>
>> --
>> 2.43.0
> 
> 
> Best Regards,
> Yan, Zi