From: ZhangPeng <zhangpeng362@huawei.com> maillist inclusion category: performance bugzilla: https://gitee.com/openeuler/kernel/issues/I9CKXN CVE: NA Reference: https://lore.kernel.org/all/20240327090835.3232629-1-zhangpeng362@huawei.com... -------------------------------- When vma->vm_userfaultfd_ctx.ctx is NULL, vma->vm_flags should have cleared __VM_UFFD_FLAGS. Therefore, there is no need to down_write or clear the flag, which will affect fork performance. Fix this by returning early if octx is NULL in dup_userfaultfd(). By applying this patch we can get a 1.3% performance improvement for lmbench fork_prot. Results are as follows: base early return Process fork+exit: 419.1106 413.4804 Link: https://lkml.kernel.org/r/20240327090835.3232629-1-zhangpeng362@huawei.com Signed-off-by: ZhangPeng <zhangpeng362@huawei.com> Reviewed-by: Peter Xu <peterx@redhat.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: David Hildenbrand <david@redhat.com> Cc: Kefeng Wang <wangkefeng.wang@huawei.com> Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Lokesh Gidra <lokeshgidra@google.com> Cc: Nanyong Sun <sunnanyong@huawei.com> Cc: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: ZhangPeng <zhangpeng362@huawei.com> --- fs/userfaultfd.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 4db4a6b8a4a3..789c8328b24a 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -707,7 +707,10 @@ int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs) struct userfaultfd_fork_ctx *fctx; octx = vma->vm_userfaultfd_ctx.ctx; - if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) { + if (!octx) + return 0; + + if (!(octx->features & UFFD_FEATURE_EVENT_FORK)) { vma_start_write(vma); vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; userfaultfd_set_vm_flags(vma, vma->vm_flags & ~__VM_UFFD_FLAGS); -- 2.25.1