On Thu, Aug 8, 2024 at 10:58 AM Jason Wang <jasowang@xxxxxxxxxx> wrote: > > On Wed, Aug 7, 2024 at 2:52 PM Yongji Xie <xieyongji@xxxxxxxxxxxxx> wrote: > > > > On Mon, Aug 5, 2024 at 4:21 PM Jason Wang <jasowang@xxxxxxxxxx> wrote: > > > > > > Barry said [1]: > > > > > > """ > > > mm doesn't support non-blockable __GFP_NOFAIL allocation. Because > > > __GFP_NOFAIL without direct reclamation may just result in a busy > > > loop within non-sleepable contexts. > > > ""“ > > > > > > Unfortuantely, we do that under read lock. A possible way to fix that > > > is to move the pages allocation out of the lock into the caller, but > > > having to allocate a huge number of pages and auxiliary page array > > > seems to be problematic as well per Tetsuon [2]: > > > > > > """ > > > You should implement proper error handling instead of using > > > __GFP_NOFAIL if count can become large. > > > """ > > > > > > So I choose another way, which does not release kernel bounce pages > > > when user tries to register usersapce bounce pages. Then we don't need > > > to do allocation in the path which is not expected to be fail (e.g in > > > the release). We pay this for more memory usage but further > > > optimizations could be done on top. > > > > > > [1] https://lore.kernel.org/all/CACGkMEtcOJAA96SF9B8m-nZ1X04-XZr+nq8ZQ2saLnUdfOGOLg@xxxxxxxxxxxxxx/T/#m3caef86a66ea6318ef94f9976ddb3a0ccfe6fcf8 > > > [2] https://lore.kernel.org/all/CACGkMEtcOJAA96SF9B8m-nZ1X04-XZr+nq8ZQ2saLnUdfOGOLg@xxxxxxxxxxxxxx/T/#m7ad10eaba48ade5abf2d572f24e185d9fb146480 > > > > > > Fixes: 6c77ed22880d ("vduse: Support using userspace pages as bounce buffer") > > > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx> > > > --- > > > > Reviewed-by: Xie Yongji <xieyongji@xxxxxxxxxxxxx> > > Tested-by: Xie Yongji <xieyongji@xxxxxxxxxxxxx> > > Thanks. > > > > > Have tested it with qemu-storage-daemon [1]: > > > > $ qemu-storage-daemon \ > > --chardev socket,id=charmonitor,path=/tmp/qmp.sock,server=on,wait=off \ > > --monitor chardev=charmonitor \ > > --blockdev driver=host_device,cache.direct=on,aio=native,filename=/dev/nullb0,node-name=disk0 > > \ > > --export type=vduse-blk,id=vduse-test,name=vduse-test,node-name=disk0,writable=on > > > > [1] https://github.com/bytedance/qemu/tree/vduse-umem > > Great, would you want to post them to the Qemu? > Looks like qemu-storage-daemon would not benefit from this feature which is designed for some hugepage users such as SPDK/DPDK. Thanks, Yongji
