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

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Message-ID: <dbd4499a-8359-6d59-83f6-50f8dba84747@huaweicloud.com>
Date: Wed, 14 Aug 2024 15:46:47 +0800
From: Hou Tao <houtao@...weicloud.com>
To: Jingbo Xu <jefflexu@...ux.alibaba.com>, linux-fsdevel@...r.kernel.org
Cc: Miklos Szeredi <miklos@...redi.hu>, Vivek Goyal <vgoyal@...hat.com>,
 Stefan Hajnoczi <stefanha@...hat.com>,
 Bernd Schubert <bernd.schubert@...tmail.fm>,
 "Michael S . Tsirkin" <mst@...hat.com>, Matthew Wilcox
 <willy@...radead.org>, Benjamin Coddington <bcodding@...hat.com>,
 linux-kernel@...r.kernel.org, virtualization@...ts.linux.dev,
 houtao1@...wei.com
Subject: Re: [PATCH v3 0/2] virtiofs: fix the warning for kernel direct IO

Hi,

On 8/14/2024 2:34 PM, Jingbo Xu wrote:
> Hi, Tao,
>
> On 4/26/24 10:39 PM, Hou Tao wrote:
>> From: Hou Tao <houtao1@...wei.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.

Being busy with other stuff these days. I hope to send v4 before next
weekend.
>
> [1]
> https://lore.kernel.org/linux-fsdevel/20240103105929.1902658-1-houtao@huaweicloud.com/
>