linux-kernel - Re: [PATCH v3] 9p: Use kvmalloc for message buffers on supported transports

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Message-ID: <aQhfVa_jdI_1kQwB@codewreck.org>
Date: Mon, 3 Nov 2025 16:52:53 +0900
From: asmadeus <asmadeus@...ewreck.org>
To: Pierre Barre <pierre@...re.sh>
Cc: Christian Schoenebeck <linux_oss@...debyte.com>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	v9fs@...ts.linux.dev, ericvh@...nel.org, lucho@...kov.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] 9p: Use kvmalloc for message buffers on supported
 transports

Pierre Barre wrote on Thu, Oct 16, 2025 at 03:58:36PM +0200:
> While developing a 9P server (https://github.com/Barre/ZeroFS) and
> testing it under high-load, I was running into allocation failures.
> The failures occur even with plenty of free memory available because
> kmalloc requires contiguous physical memory.
> 
> This results in errors like:
> ls: page allocation failure: order:7, mode:0x40c40(GFP_NOFS|__GFP_COMP)
> 
> This patch introduces a transport capability flag (supports_vmalloc)
> that indicates whether a transport can work with vmalloc'd buffers
> (non-physically contiguous memory). Transports requiring DMA should
> leave this flag as false.
> 
> The fd-based transports (tcp, unix, fd) set this flag to true, and
> p9_fcall_init will use kvmalloc instead of kmalloc for these
> transports. This allows the allocator to fall back to vmalloc when
> contiguous physical memory is not available.
> 
> Additionally, if kmem_cache_alloc fails, the code falls back to
> kvmalloc for transports that support it.
> 
> Signed-off-by: Pierre Barre <pierre@...re.sh>

Thanks, it's now picked up and queued in -next -- will send to Linus in
a couple of months.

FWIW, I prefer (and I think it's the norm in the linux world) if patches
new versions aren't sent as a reply to previous version, it confuses
tools like b4 that fetch the patch thread for version operations.
If you send patches again please just send later versions without
using --in-reply-to :)

Cheers,
-- 
Dominique Martinet | Asmadeus