Re: [PATCH v3 0/2] virtiofs: fix the warning for kernel direct IO

[Jingbo Xu <jefflexu@linux.alibaba.com>]

Hi, Tao,

On 4/26/24 10:39 PM, Hou Tao wrote:
> From: Hou Tao <houtao1@huawei.com>
> 
> Hi,
> 
> The patch set aims to fix the warning related to an abnormal size
> parameter of kmalloc() in virtiofs. Patch #1 fixes it by introducing
> use_pages_for_kvec_io option in fuse_conn and enabling it in virtiofs.
> Beside the abnormal size parameter for kmalloc, the gfp parameter is
> also questionable: GFP_ATOMIC is used even when the allocation occurs
> in a kworker context. Patch #2 fixes it by using GFP_NOFS when the
> allocation is initiated by the kworker. For more details, please check
> the individual patches.
> 
> As usual, comments are always welcome.
> 
> Change Log:
> 
> v3:
>  * introduce use_pages_for_kvec_io for virtiofs. When the option is
>    enabled, fuse will use iov_iter_extract_pages() to construct a page
>    array and pass the pages array instead of a pointer to virtiofs.
>    The benefit is twofold: the length of the data passed to virtiofs is
>    limited by max_pages, and there is no memory copy compared with v2.
> 
> v2: https://lore.kernel.org/linux-fsdevel/20240228144126.2864064-1-houtao@huaweicloud.com/
>   * limit the length of ITER_KVEC dio by max_pages instead of the
>     newly-introduced max_nopage_rw. Using max_pages make the ITER_KVEC
>     dio being consistent with other rw operations.
>   * replace kmalloc-allocated bounce buffer by using a bounce buffer
>     backed by scattered pages when the length of the bounce buffer for
>     KVEC_ITER dio is larger than PAG_SIZE, so even on hosts with
>     fragmented memory, the KVEC_ITER dio can be handled normally by
>     virtiofs. (Bernd Schubert)
>   * merge the GFP_NOFS patch [1] into this patch-set and use
>     memalloc_nofs_{save|restore}+GFP_KERNEL instead of GFP_NOFS
>     (Benjamin Coddington)
> 
> v1: https://lore.kernel.org/linux-fsdevel/20240103105929.1902658-1-houtao@huaweicloud.com/
> 
> [1]: https://lore.kernel.org/linux-fsdevel/20240105105305.4052672-1-houtao@huaweicloud.com/
> 
> Hou Tao (2):
>   virtiofs: use pages instead of pointer for kernel direct IO
>   virtiofs: use GFP_NOFS when enqueuing request through kworker
> 
>  fs/fuse/file.c      | 12 ++++++++----
>  fs/fuse/fuse_i.h    |  3 +++
>  fs/fuse/virtio_fs.c | 25 ++++++++++++++++---------
>  3 files changed, 27 insertions(+), 13 deletions(-)
> 

We also encountered the same issue as [1] these days when attempting to
insmod a module with ~6MB size, which is upon a virtiofs filesystem.

It would be much helpful if this issue has a standard fix in the
upstream.  I see there will be v4 when reading through the mailing
thread.  Glad to know if there's any update to this series.

[1]
https://lore.kernel.org/linux-fsdevel/20240103105929.1902658-1-houtao@huaweicloud.com/

-- 
Thanks,
Jingbo