Re: [PATCH] userfaultfd: early return in dup_userfaultfd()

[Peter Xu]

On Wed, Mar 27, 2024 at 05:08:35PM +0800, Peng Zhang wrote:
> From: ZhangPeng <zhangpeng362@xxxxxxxxxx>
> 
> 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
> 
> Signed-off-by: ZhangPeng <zhangpeng362@xxxxxxxxxx>

Reviewed-by: Peter Xu <peterx@xxxxxxxxxx>

-- 
Peter Xu