From: Huang Ying <ying.huang@xxxxxxxxx> To help people understand the MADV_FREE code, especially the page flag, PG_swapbacked. Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx> Suggested-by: David Hildenbrand <david@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxxx> --- include/linux/mm_inline.h | 9 +++++---- include/linux/page-flags.h | 4 ++++ mm/swap.c | 6 +++--- 3 files changed, 12 insertions(+), 7 deletions(-) diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h index 6f2fef7b0784..01144dd02a5f 100644 --- a/include/linux/mm_inline.h +++ b/include/linux/mm_inline.h @@ -9,10 +9,11 @@ * page_is_file_cache - should the page be on a file LRU or anon LRU? * @page: the page to test * - * Returns 1 if @page is page cache page backed by a regular filesystem, - * or 0 if @page is anonymous, tmpfs or otherwise ram or swap backed. - * Used by functions that manipulate the LRU lists, to sort a page - * onto the right LRU list. + * Returns 1 if @page is page cache page backed by a regular filesystem or + * anonymous page lazily freed (e.g. via MADV_FREE). Returns 0 if @page is + * normal anonymous page, tmpfs or otherwise ram or swap backed. Used by + * functions that manipulate the LRU lists, to sort a page onto the right LRU + * list. * * We would like to get this info without a page flag, but the state * needs to survive until the page is last deleted from the LRU, which diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 49c2697046b9..992b71c4fc85 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -63,6 +63,10 @@ * page_waitqueue(page) is a wait queue of all tasks waiting for the page * to become unlocked. * + * PG_swapbacked is cleared if the page is page cache page backed by a regular + * file system or anonymous page lazily freed (e.g. via MADV_FREE). It is set + * if the page is normal anonymous page, tmpfs or otherwise RAM or swap backed. + * * PG_uptodate tells whether the page's contents is valid. When a read * completes, the page becomes uptodate, unless a disk I/O error happened. * diff --git a/mm/swap.c b/mm/swap.c index 6a8be910b14d..90bb14695809 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -573,9 +573,9 @@ static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec, ClearPageActive(page); ClearPageReferenced(page); /* - * lazyfree pages are clean anonymous pages. They have - * SwapBacked flag cleared to distinguish normal anonymous - * pages + * Lazyfree pages are clean anonymous pages. They + * have PG_swapbacked flag cleared, to distinguish + * them from normal anonymous pages */ ClearPageSwapBacked(page); add_page_to_lru_list(page, lruvec, LRU_INACTIVE_FILE); -- 2.25.0
