linux-kernel - Re: [RFC PATCH] mm: net: disable kswapd for high-order network buffer allocation

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Message-ID: <CAGsJ_4x9=Be2Prbjia8-p97zAsoqjsPHkZOfXwz74Z_T=RjKAA@mail.gmail.com>
Date: Tue, 14 Oct 2025 12:09:19 +0800
From: Barry Song <21cnbao@...il.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: netdev@...r.kernel.org, linux-mm@...ck.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Barry Song <v-songbaohua@...o.com>, 
	Jonathan Corbet <corbet@....net>, Eric Dumazet <edumazet@...gle.com>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, Paolo Abeni <pabeni@...hat.com>, 
	Willem de Bruijn <willemb@...gle.com>, "David S. Miller" <davem@...emloft.net>, 
	Jakub Kicinski <kuba@...nel.org>, Simon Horman <horms@...nel.org>, Vlastimil Babka <vbabka@...e.cz>, 
	Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>, 
	Brendan Jackman <jackmanb@...gle.com>, Johannes Weiner <hannes@...xchg.org>, Zi Yan <ziy@...dia.com>, 
	Yunsheng Lin <linyunsheng@...wei.com>, Huacai Zhou <zhouhuacai@...o.com>
Subject: Re: [RFC PATCH] mm: net: disable kswapd for high-order network buffer allocation

On Tue, Oct 14, 2025 at 5:56 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Mon, Oct 13, 2025 at 06:16:36PM +0800, Barry Song wrote:
> > On phones, we have observed significant phone heating when running apps
> > with high network bandwidth. This is caused by the network stack frequently
> > waking kswapd for order-3 allocations. As a result, memory reclamation becomes
> > constantly active, even though plenty of memory is still available for network
> > allocations which can fall back to order-0.
>
> I think we need to understand what's going on here a whole lot more than
> this!
>
> So, we try to do an order-3 allocation.  kswapd runs and ... succeeds in
> creating order-3 pages?  Or fails to?
>

Our team observed that most of the time we successfully obtain order-3
memory, but the cost is excessive memory reclamation, since we end up
over-reclaiming order-0 pages that could have remained in memory.

> If it fails, that's something we need to sort out.
>
> If it succeeds, now we have several order-3 pages, great.  But where do
> they all go that we need to run kswapd again?

The network app keeps running and continues to issue new order-3 allocation
requests, so those few order-3 pages won’t be enough to satisfy the
continuous demand.

Thanks
Barry