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

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Message-ID: <D9734C47-0EDA-4154-8889-1B789B49322F@nvidia.com>
Date: Mon, 05 Jan 2026 11:36:20 -0500
From: Zi Yan <ziy@...dia.com>
To: Ryan Roberts <ryan.roberts@....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 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.

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