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authorZhangPeng2024-03-27 17:08:35 +0800
committerAndrew Morton2024-04-25 20:56:25 -0700
commitafd584398b51eba12d0ffa4e0e0a493323993103 (patch)
treeb4a25841bb77576d694d669cd491ce321413d645 /fs/userfaultfd.c
parent08b8247ebd2b70367ab3a87657efb237662bd8f6 (diff)
userfaultfd: early return in dup_userfaultfd()
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>
Diffstat (limited to 'fs/userfaultfd.c')
-rw-r--r--fs/userfaultfd.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 60dcfafdc11a..3e6ddda6f159 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -657,7 +657,10 @@ 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);