diff options
| author | ZhangPeng <zhangpeng362@huawei.com> | 2024-03-27 17:08:35 +0800 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2024-04-25 20:56:25 -0700 |
| commit | afd584398b51eba12d0ffa4e0e0a493323993103 (patch) | |
| tree | b4a25841bb77576d694d669cd491ce321413d645 | |
| parent | 08b8247ebd2b70367ab3a87657efb237662bd8f6 (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>
| -rw-r--r-- | fs/userfaultfd.c | 5 |
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); |