linux-kernel - Re: [PATCH 2/2] mm/vmalloc: Add attempt_larger_order

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Message-ID: <aUKV-RZE8QjHQ0PW@milan>
Date: Wed, 17 Dec 2025 12:37:29 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Uladzislau Rezki (Sony)" <urezki@...il.com>, linux-mm@...ck.org,
	Vishal Moola <vishal.moola@...il.com>,
	Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
	Baoquan He <bhe@...hat.com>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm/vmalloc: Add attempt_larger_order_alloc parameter

On Tue, Dec 16, 2025 at 03:36:04PM -0800, Andrew Morton wrote:
> On Tue, 16 Dec 2025 22:19:21 +0100 "Uladzislau Rezki (Sony)" <urezki@...il.com> wrote:
> 
> > Introduce a module parameter to enable or disable the large-order
> > allocation path in vmalloc. High-order allocations are disabled by
> > default so far, but users may explicitly enable them at runtime if
> > desired.
> > 
> > High-order pages allocated for vmalloc are immediately split into
> > order-0 pages and later freed as order-0, which means they do not
> > feed the per-CPU page caches. As a result, high-order attempts tend
> > to bypass the PCP fastpath and fall back to the buddy allocator that
> > can affect performance.
> > 
> > However, when the PCP caches are empty, high-order allocations may
> > show better performance characteristics especially for larger
> > allocation requests.
> > 
> > Since the best strategy is workload-dependent, this patch adds a
> > parameter letting users to choose whether vmalloc should try
> > high-order allocations or stay strictly on the order-0 fastpath.
> > 
> > ...
> >
> > +module_param(attempt_larger_order_alloc, int, 0644);
> 
> We should have user docs, please.  Probably in kernel-parameters.txt.
>
Thanks. I will add it.

--
Uladzislau Rezki