netdev - Re: [PATCH] mm: Decline to manipulate the refcount on a slab page

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Message-ID: <Z9Ef75c1ffTWGU_c@infradead.org>
Date: Tue, 11 Mar 2025 22:47:27 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>, netdev@...r.kernel.org,
	Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
	Hannes Reinecke <hare@...e.de>
Subject: Re: [PATCH] mm: Decline to manipulate the refcount on a slab page

On Tue, Mar 11, 2025 at 11:15:11AM +0100, Jakub Kicinski wrote:
> On Mon, 10 Mar 2025 14:35:24 +0000 Matthew Wilcox (Oracle) wrote:
> > Long-term, networking needs to stop taking a refcount on the pages that
> > it uses and rely on the caller to hold whatever references are necessary
> > to make the memory stable. 
> 
> TBH I'm not clear on who is going to fix this.
> IIRC we already told NVMe people that sending slab memory over sendpage 
> is not well supported. Plus the bug is in BPF integration, judging by
> the stack traces (skmsg is a BPF thing). Joy.

slab over sendpage doesn't work because you refuse to take the patches
to make it work by transparently falling back to sendmsg.  It's a giant
pain for all network storage drivers caused by the networking
maintainers.  The ultimate root cause is the fact that networking messes
with the refcounts.