On Sat, Jul 31, 2021 at 12:39:38AM -0600, Yu Zhao wrote:
> +++ b/mm/migrate.c
> @@ -168,14 +168,53 @@ void putback_movable_pages(struct list_head *l)
> }
> }
>
> +static bool try_to_unmap_clean(struct page_vma_mapped_walk *pvmw, struct page *page)
> +{
> + void *addr;
> + bool dirty;
> +
> + VM_BUG_ON_PAGE(PageLRU(page), page);
> + VM_BUG_ON_PAGE(PageCompound(page), page);
> + VM_BUG_ON_PAGE(!PageAnon(page), page);
> + VM_BUG_ON_PAGE(!PageLocked(page), page);
> + VM_BUG_ON_PAGE(pte_present(*pvmw->pte), page);
> +
> + if (PageMlocked(page) || (pvmw->vma->vm_flags & VM_LOCKED))
> + return false;
> +
> + /*
> + * The pmd entry mapping the old thp was flushed and the pte mapping
> + * this subpage has been non present. Therefore, this subpage is
> + * inaccessible. We don't need to remap it if it contains only zeros.
> + */
> + addr = kmap_atomic(page);
> + dirty = !!memchr_inv(addr, 0, PAGE_SIZE);
> + kunmap_atomic(addr);
kmap_local() is preferred now. Also, Linus has a particular hatred for
the !! idiom; just compare against NULL.
