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Subject: Re: [PATCH] virtiofs: limit the length of ITER_KVEC dio by
 max_nopage_rw
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: linux-fsdevel@vger.kernel.org, Miklos Szeredi <miklos@szeredi.hu>,
 Vivek Goyal <vgoyal@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>,
 linux-kernel@vger.kernel.org, virtualization@lists.linux.dev,
 houtao1@huawei.com, Bernd Schubert <bernd.schubert@fastmail.fm>
References: <20240103105929.1902658-1-houtao@huaweicloud.com>
 <20240222144828-mutt-send-email-mst@kernel.org>
From: Hou Tao <houtao@huaweicloud.com>
Message-ID: <2fe9376d-27a6-d502-9acb-3890b3d3946f@huaweicloud.com>
Date: Fri, 23 Feb 2024 08:58:30 +0800
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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@huawei.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@huawei.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.