On Mon, Sep 15, 2025 at 3:34 PM <[email protected]> wrote: > > From: Sheng Zhao <[email protected]> > > The allocation granularity of bounce pages is PAGE_SIZE. This may cause > even small IO requests to occupy an entire bounce page exclusively. The > kind of memory waste will be more significant on arm64 with 64KB pages.
Let's tweak the title as there are archs that are using non 4KB pages other than arm. > > So, optimize it by using fixed 4KB bounce pages. > > Signed-off-by: Sheng Zhao <[email protected]> > --- > drivers/vdpa/vdpa_user/iova_domain.c | 120 +++++++++++++++++---------- > drivers/vdpa/vdpa_user/iova_domain.h | 5 ++ > 2 files changed, 83 insertions(+), 42 deletions(-) > > diff --git a/drivers/vdpa/vdpa_user/iova_domain.c > b/drivers/vdpa/vdpa_user/iova_domain.c > index 58116f89d8da..768313c80b62 100644 > --- a/drivers/vdpa/vdpa_user/iova_domain.c > +++ b/drivers/vdpa/vdpa_user/iova_domain.c > @@ -103,19 +103,26 @@ void vduse_domain_clear_map(struct vduse_iova_domain > *domain, > static int vduse_domain_map_bounce_page(struct vduse_iova_domain *domain, > u64 iova, u64 size, u64 paddr) > { > - struct vduse_bounce_map *map; > + struct vduse_bounce_map *map, *head_map; > + struct page *tmp_page; > u64 last = iova + size - 1; > > while (iova <= last) { > - map = &domain->bounce_maps[iova >> PAGE_SHIFT]; > + map = &domain->bounce_maps[iova >> BOUNCE_PAGE_SHIFT]; BOUNCE_PAGE_SIZE is kind of confusing as it's not the size of any page at all when PAGE_SIZE is not 4K. > if (!map->bounce_page) { > - map->bounce_page = alloc_page(GFP_ATOMIC); > - if (!map->bounce_page) > - return -ENOMEM; > + head_map = &domain->bounce_maps[(iova & PAGE_MASK) >> > BOUNCE_PAGE_SHIFT]; > + if (!head_map->bounce_page) { > + tmp_page = alloc_page(GFP_ATOMIC); > + if (!tmp_page) > + return -ENOMEM; > + if (cmpxchg(&head_map->bounce_page, NULL, > tmp_page)) > + __free_page(tmp_page); I don't understand why we need cmpxchg() logic. Btw, it looks like you want to make multiple bounce_map to point to the same 64KB page? I wonder what's the advantages of doing this. Can we simply keep the 64KB page in bounce_map? Thanks
