linux-kernel - Re: [PATCH] virtiofs: limit the length of ITER_KVEC dio by max_nopage

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Date: Fri, 23 Feb 2024 08:58:30 +0800
From: Hou Tao <houtao@...weicloud.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: linux-fsdevel@...r.kernel.org, Miklos Szeredi <miklos@...redi.hu>,
 Vivek Goyal <vgoyal@...hat.com>, Stefan Hajnoczi <stefanha@...hat.com>,
 linux-kernel@...r.kernel.org, virtualization@...ts.linux.dev,
 houtao1@...wei.com, Bernd Schubert <bernd.schubert@...tmail.fm>
Subject: Re: [PATCH] virtiofs: limit the length of ITER_KVEC dio by
 max_nopage_rw

Hi,

On 2/23/2024 3:49 AM, Michael S. Tsirkin wrote:
> On Wed, Jan 03, 2024 at 06:59:29PM +0800, Hou Tao wrote:
>> From: Hou Tao <houtao1@...wei.com>
>>
>> When trying to insert a 10MB kernel module kept in a virtiofs with cache
>> disabled, the following warning was reported:
>>

SNIP

>>
>> A feasible solution is to limit the value of max_read for virtiofs, so
>> the length passed to kmalloc() will be limited. However it will affects
>> the max read size for ITER_IOVEC io and the value of max_write also needs
>> limitation. So instead of limiting the values of max_read and max_write,
>> introducing max_nopage_rw to cap both the values of max_read and
>> max_write when the fuse dio read/write request is initiated from kernel.
>>
>> Considering that fuse read/write request from kernel is uncommon and to
>> decrease the demand for large contiguous pages, set max_nopage_rw as
>> 256KB instead of KMALLOC_MAX_SIZE - 4096 or similar.
>>
>> Fixes: a62a8ef9d97d ("virtio-fs: add virtiofs filesystem")
>> Signed-off-by: Hou Tao <houtao1@...wei.com>
>
> So what should I do with this patch? It includes fuse changes
> but of course I can merge too if no one wants to bother either way...

The patch had got some feedback from Bernd Schubert . And I will post v2
before next Thursday.