Re: [PATCH 4/5] mm: Do early cow for pinned pages during fork() for ptes

Oleg Nesterov
2020-09-22T18:44:17Z

On 09/22, Peter Xu wrote:
>
> Or I can also do it in inverted order if you think better:
>
> if (unlikely(copy_ret == COPY_MM_BREAK_COW)) {
> WARN_ON_ONCE(!data.cow_new_page);
> ...
> }

Peter, let me say this again. I don't understand this code enough, you
can safely ignore me ;)

However. Personally I strongly prefer the above. Personally I really
dislike this part of 4/5:

again:
+ /* We don't reset this for COPY_MM_BREAK_COW */
+ memset(&data, 0, sizeof(data));
+
+again_break_cow:

If we rely on "copy_ret == COPY_MM_BREAK_COW" we can unify "again" and
"again_break_cow", we don't need to clear ->cow_new_page, this makes the
logic more understandable. To me at least ;)

Oleg.