Hi,

On 5/10/2024 7:19 PM, Miklos Szeredi wrote:

On Fri, 26 Apr 2024 at 16:38, Hou Tao [off-list ref] wrote:

quoted

From: Hou Tao <redacted>

When invoking virtio_fs_enqueue_req() through kworker, both the
allocation of the sg array and the bounce buffer still use GFP_ATOMIC.
Considering the size of the sg array may be greater than PAGE_SIZE, use
GFP_NOFS instead of GFP_ATOMIC to lower the possibility of memory
allocation failure and to avoid unnecessarily depleting the atomic
reserves. GFP_NOFS is not passed to virtio_fs_enqueue_req() directly,
GFP_KERNEL and memalloc_nofs_{save|restore} helpers are used instead.

Makes sense.

However, I don't understand why the GFP_NOFS behavior is optional. It
should work when queuing the request for the first time as well, no?

No. fuse_request_queue_background() may call queue_request_and_unlock()
with fc->bg_lock being held and bg_lock is a spin-lock, so as for now it
is bad to call kmalloc(GFP_NOFS) with a spin-lock being held. The
acquisition of fc->bg_lock in  fuse_request_queue_background() may could
be optimized, but I will leave it for future work.

Thanks,
Miklos
.