Re: [PATCH v3] mm: memory: check userfaultfd_wp() in vmf_orig_pte_uffd_wp()

[Peter Xu <peterx@redhat.com>]

On Mon, Apr 22, 2024 at 11:00:39AM +0800, Kefeng Wang wrote:
> Adding userfaultfd_wp() check in vmf_orig_pte_uffd_wp() to avoid the
> unnecessary FAULT_FLAG_ORIG_PTE_VALID check/pte_marker_entry_uffd_wp()
> in most pagefault, note, the function vmf_orig_pte_uffd_wp() is not
> inlined in the two kernel versions, the difference is shown below,
> 
> perf date,
> 
>   perf report -i perf.data.before | grep vmf
>      0.17%     0.13%  lat_pagefault  [kernel.kallsyms]      [k] vmf_orig_pte_uffd_wp.part.0.isra.0
>   perf report -i perf.data.after  | grep vmf
> 
> lat_pagefault -W 5 -N 5 /tmp/XXX
>   latency              before        after        diff
>   average(8 tests)     0.262675      0.2600375   -0.0026375
> 
> Although it's a small, but the uffd_wp is a new feature than previous
> kernel, when the vma is not registered with UFFD_WP, let's avoid to
> execute the new logical, also adding __always_inline attribute to 
> vmf_orig_pte_uffd_wp(), which make set_pte_range() only check VM_UFFD_WP
> flags without the function call. In addition, directly call the
> vmf_orig_pte_uffd_wp() in do_anonymous_page() and set_pte_range()
> to save an uffd_wp variable.
> 
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu