On 2/21/20 10:53 PM, Rik van Riel wrote:
> @@ -981,7 +981,9 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> if (__isolate_lru_page(page, isolate_mode) != 0)
> goto isolate_fail;
>
> - VM_BUG_ON_PAGE(PageCompound(page), page);
> + /* The whole page is taken off the LRU; skip the tail pages. */
> + if (PageCompound(page))
> + low_pfn += compound_nr(page) - 1;
>
> /* Successfully isolated */
> del_page_from_lru_list(page, lruvec, page_lru(page));
This continues by:
inc_node_page_state(page, NR_ISOLATED_ANON + page_is_file_cache(page));
I think it now needs to use mod_node_page_state() with
hpage_nr_pages(page) otherwise the counter will underflow after the
migration?
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index a36736812596..38c8ddfcecc8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8253,14 +8253,16 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
>
> /*
> * Hugepages are not in LRU lists, but they're movable.
> + * THPs are on the LRU, but need to be counted as #small pages.
> * We need not scan over tail pages because we don't
> * handle each tail page individually in migration.
> */
> - if (PageHuge(page)) {
> + if (PageTransHuge(page)) {
Hmm, PageTransHuge() has VM_BUG_ON() for tail pages, while this code is
written so that it can encounter a tail page and skip the rest of the
compound page properly. So I would be worried about this.
Also PageTransHuge() is basically just a PageHead() so for each
non-hugetlbfs compound page this will assume it's a THP, while correctly
it should reach the __PageMovable() || PageLRU(page) tests below.
So probably this should do something like.
if (PageHuge(page) || PageTransCompound(page)) {
...
if (PageHuge(page) && !hpage_migration_supported)) return page.
if (!PageLRU(head) && !__PageMovable(head)) return page
...
> struct page *head = compound_head(page);
> unsigned int skip_pages;
>
> - if (!hugepage_migration_supported(page_hstate(head)))
> + if (PageHuge(page) &&
> + !hugepage_migration_supported(page_hstate(head)))
> return page;
>
> skip_pages = compound_nr(head) - (page - head);
>
