On Wed, Feb 28, 2024 at 10:41:20PM +0800, Hou Tao wrote:
> From: Hou Tao <hout...@huawei.com>
>
> Hi,
>
> The patch set aims to fix the warning related to an abnormal size
> parameter of kmalloc() in virtiofs. The warning occurred when attempting
> to insert a 10MB sized kernel module kept in a virtiofs with cache
> disabled. As analyzed in patch #1, the root cause is that the length of
> the read buffer is no limited, and the read buffer is passed directly to
> virtiofs through out_args[0].value. Therefore patch #1 limits the
> length of the read buffer passed to virtiofs by using max_pages. However
> it is not enough, because now the maximal value of max_pages is 256.
> Consequently, when reading a 10MB-sized kernel module, the length of the
> bounce buffer in virtiofs will be 40 + (256 * 4096), and kmalloc will
> try to allocate 2MB from memory subsystem. The request for 2MB of
> physically contiguous memory significantly stress the memory subsystem
> and may fail indefinitely on hosts with fragmented memory. To address
> this, patch #2~#5 use scattered pages in a bio_vec to replace the
> kmalloc-allocated bounce buffer when the length of the bounce buffer for
> KVEC_ITER dio is larger than PAGE_SIZE. The final issue with the
> allocation of the bounce buffer and sg array in virtiofs is that
> GFP_ATOMIC is used even when the allocation occurs in a kworker context.
> Therefore the last patch uses GFP_NOFS for the allocation of both sg
> array and bounce buffer when initiated by the kworker. For more details,
> please check the individual patches.
>
> As usual, comments are always welcome.
>
> Change Log:
Bernd should I just merge the patchset as is?
It seems to fix a real problem and no one has the
time to work on a better fix .... WDYT?
> v2:
> * 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-hou...@huaweicloud.com/
>
> [1]:
> https://lore.kernel.org/linux-fsdevel/20240105105305.4052672-1-hou...@huaweicloud.com/
>
> Hou Tao (6):
> fuse: limit the length of ITER_KVEC dio by max_pages
> virtiofs: move alloc/free of argbuf into separated helpers
> virtiofs: factor out more common methods for argbuf
> virtiofs: support bounce buffer backed by scattered pages
> virtiofs: use scattered bounce buffer for ITER_KVEC dio
> virtiofs: use GFP_NOFS when enqueuing request through kworker
>
> fs/fuse/file.c | 12 +-
> fs/fuse/virtio_fs.c | 336 +++++++++++++++++++++++++++++++++++++-------
> 2 files changed, 296 insertions(+), 52 deletions(-)
>
> --
> 2.29.2
