Commit c3096e67 authored by Hugh Dickins's avatar Hugh Dickins Committed by Matthew Wilcox (Oracle)
Browse files

mm/migrate: __unmap_and_move() push good newpage to LRU 



Compaction, NUMA page movement, THP collapse/split, and memory failure
do isolate unevictable pages from their "LRU", losing the record of
mlock_count in doing so (isolators are likely to use page->lru for their
own private lists, so mlock_count has to be presumed lost).

That's unfortunate, and we should put in some work to correct that: one
can imagine a function to build up the mlock_count again - but it would
require i_mmap_rwsem for read, so be careful where it's called.  Or
page_referenced_one() and try_to_unmap_one() might do that extra work.

But one place that can very easily be improved is page migration's
__unmap_and_move(): a small adjustment to where the successful new page
is put back on LRU, and its mlock_count (if any) is built back up by
remove_migration_ptes().

Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
parent 34b67923

mm/migrate.c

+19 −12
Original line number Diff line number Diff line
@@ -1032,6 +1032,21 @@ static int __unmap_and_move(struct page *page, struct page *newpage, 
	if (!page_mapped(page))

		rc = move_to_new_page(newpage, page, mode);



	/*

	 * When successful, push newpage to LRU immediately: so that if it

	 * turns out to be an mlocked page, remove_migration_ptes() will

	 * automatically build up the correct newpage->mlock_count for it.

	 *

	 * We would like to do something similar for the old page, when

	 * unsuccessful, and other cases when a page has been temporarily

	 * isolated from the unevictable LRU: but this case is the easiest.

	 */

	if (rc == MIGRATEPAGE_SUCCESS) {

		lru_cache_add(newpage);

		if (page_was_mapped)

			lru_add_drain();

	}



	if (page_was_mapped)

		remove_migration_ptes(page,

			rc == MIGRATEPAGE_SUCCESS ? newpage : page, false);
@@ -1045,20 +1060,12 @@ static int __unmap_and_move(struct page *page, struct page *newpage, 
	unlock_page(page);

out:

	/*

	 * If migration is successful, decrease refcount of the newpage

	 * If migration is successful, decrease refcount of the newpage,

	 * which will not free the page because new page owner increased

	 * refcounter. As well, if it is LRU page, add the page to LRU

	 * list in here. Use the old state of the isolated source page to

	 * determine if we migrated a LRU page. newpage was already unlocked

	 * and possibly modified by its owner - don't rely on the page

	 * state.

	 * refcounter.

	 */

	if (rc == MIGRATEPAGE_SUCCESS) {

		if (unlikely(!is_lru))

	if (rc == MIGRATEPAGE_SUCCESS)

		put_page(newpage);

		else

			putback_lru_page(newpage);

	}



	return rc;

}