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

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Message-Id: <20251216153604.0c00504223d3fad070f2e803@linux-foundation.org>
Date: Tue, 16 Dec 2025 15:36:04 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc: 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, 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.