On Fri, Feb 19, 2021 at 10:56:42AM +0100, Michal Hocko wrote:
> OK, this should work but I am really wondering whether it wouldn't be
> just simpler to replace the old page by a new one in the free list
> directly. Or is there any reason we have to go through the generic
> helpers path? I mean something like this
>
> new_page = alloc_fresh_huge_page();
> if (!new_page)
> goto fail;
> spin_lock(hugetlb_lock);
> if (!PageHuge(old_page)) {
> /* freed from under us, nothing to do */
> __update_and_free_page(new_page);
> goto unlock;
> }
> list_del(&old_page->lru);
> __update_and_free_page(old_page);
> __enqueue_huge_page(new_page);
> unlock:
> spin_unlock(hugetlb_lock);
>
> This will require to split update_and_free_page and enqueue_huge_page to
> counters independent parts but that shouldn't be a big deal. But it will
> also protect from any races. Not an act of beauty but seems less hackish
> to me.
On a closer look, do we really need to decouple update_and_free_page and
enqueue_huge_page? These two functions do not handle the lock, but rather
the functions that call them (as would be in our case).
Only update_and_free_page drops the lock during the freeing of a gigantic page
and then it takes it again, as the caller is who took the lock.
am I missing anything obvious here?
--
Oscar Salvador
SUSE L3
