Hi, On 5/10/2024 7:19 PM, Miklos Szeredi wrote: > On Fri, 26 Apr 2024 at 16:38, Hou Tao <hou...@huaweicloud.com> wrote: >> From: Hou Tao <hout...@huawei.com> >> >> 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 inĀ fuse_request_queue_background() may could be optimized, but I will leave it for future work. > Thanks, > Miklos > .