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Date: Fri, 27 Mar 2026 12:42:49 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Muhammad Usama Anjum <usama.anjum@arm.com>
Cc: David Hildenbrand <david@kernel.org>, Lorenzo Stoakes <ljs@kernel.org>,
 "Liam R . Howlett" <Liam.Howlett@oracle.com>, Vlastimil Babka
 <vbabka@kernel.org>, Mike Rapoport <rppt@kernel.org>, Suren Baghdasaryan
 <surenb@google.com>, Michal Hocko <mhocko@suse.com>, Brendan Jackman
 <jackmanb@google.com>, Johannes Weiner <hannes@cmpxchg.org>, Zi Yan
 <ziy@nvidia.com>, Uladzislau Rezki <urezki@gmail.com>, Nick Terrell
 <terrelln@fb.com>, David Sterba <dsterba@suse.com>, Vishal Moola
 <vishal.moola@gmail.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org,
 bpf@vger.kernel.org, Ryan.Roberts@arm.com, david.hildenbrand@arm.com
Subject: Re: [PATCH v4 0/3] mm: Free contiguous order-0 pages efficiently
Message-Id: <20260327124249.a8de2259cf3438c5f4216894@linux-foundation.org>
In-Reply-To: <20260327125720.2270651-1-usama.anjum@arm.com>
References: <20260327125720.2270651-1-usama.anjum@arm.com>
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On Fri, 27 Mar 2026 12:57:12 +0000 Muhammad Usama Anjum <usama.anjum@arm.com> wrote:

> A recent change to vmalloc caused some performance benchmark regressions (see
> [1]). I'm attempting to fix that (and at the same time significantly 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. While at it, optimize the
> __free_contig_frozen_range() as well.
> 
> Check that the contiguous range falls in the same section. If they aren't enabled,
> the if conditions get optimized out by the compiler as memdesc_section() returns 0.
> See num_pages_contiguous() for more details about it.

Thanks.  I'm seeing impressive speedups for microbenchmarks.  The
speedup in [3/3] may be a bit more real-worldy.

Do you have a feeling for how much difference these changes will make
for any real-world workload?

Also, AI review said things:
	https://sashiko.dev/#/patchset/20260327125720.2270651-1-usama.anjum@arm.com

The can_free one (at least) seems legit.  I suggest that can_free be
made local to that for() loop - this would clear things up a bit.