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> 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 > drivers/vdpa/vdpa_user/iova_domain.c | 18 ++++++++++-------- > drivers/vdpa/vdpa_user/iova_domain.h | 1 + > 2 files changed, 11 insertions(+), 8 deletions(-) > > diff --git a/drivers/vdpa/vdpa_user/iova_domain.c b/drivers/vdpa/vdpa_user/iova_domain.c > index 791d38d6284c..933d2f7cd49a 100644 > --- a/drivers/vdpa/vdpa_user/iova_domain.c > +++ b/drivers/vdpa/vdpa_user/iova_domain.c > @@ -162,6 +162,7 @@ static void vduse_domain_bounce(struct vduse_iova_domain *domain, > enum dma_data_direction dir) > { > struct vduse_bounce_map *map; > + struct page *page; > unsigned int offset; > void *addr; > size_t sz; > @@ -178,7 +179,10 @@ static void vduse_domain_bounce(struct vduse_iova_domain *domain, > map->orig_phys == INVALID_PHYS_ADDR)) > return; > > - addr = kmap_local_page(map->bounce_page); > + page = domain->user_bounce_pages ? > + map->user_bounce_page : map->bounce_page; > + > + addr = kmap_local_page(page); > do_bounce(map->orig_phys + offset, addr + offset, sz, dir); > kunmap_local(addr); > size -= sz; > @@ -270,9 +274,8 @@ int vduse_domain_add_user_bounce_pages(struct vduse_iova_domain *domain, > memcpy_to_page(pages[i], 0, > page_address(map->bounce_page), > PAGE_SIZE); > - __free_page(map->bounce_page); > } > - map->bounce_page = pages[i]; > + map->user_bounce_page = pages[i]; > get_page(pages[i]); > } > domain->user_bounce_pages = true; > @@ -297,17 +300,16 @@ void vduse_domain_remove_user_bounce_pages(struct vduse_iova_domain *domain) > struct page *page = NULL; > > map = &domain->bounce_maps[i]; > - if (WARN_ON(!map->bounce_page)) > + if (WARN_ON(!map->user_bounce_page)) > continue; > > /* Copy user page to kernel page if it's in use */ > if (map->orig_phys != INVALID_PHYS_ADDR) { > - page = alloc_page(GFP_ATOMIC | __GFP_NOFAIL); > + page = map->bounce_page; > memcpy_from_page(page_address(page), > - map->bounce_page, 0, PAGE_SIZE); > + map->user_bounce_page, 0, PAGE_SIZE); > } > - put_page(map->bounce_page); > - map->bounce_page = page; > + put_page(map->user_bounce_page); map->user_bounce_page = NULL? Thanks, Yongji
