From: Michal Hocko <[email protected]> PGDEACTIVATE represents the number of pages moved from the active list to the inactive list. At least this sounds like the original motivation of the counter. move_active_pages_to_lru, however, counts pages which got freed in the mean time as deactivated as well. This is a very rare event and counting them as deactivation in itself is not harmful but it makes the code more convoluted than necessary - we have to count both all pages and those which are freed which is a bit confusing.
After this patch the PGDEACTIVATE should have a slightly more clear semantic and only count those pages which are moved from the active to the inactive list which is a plus. Suggested-by: Vlastimil Babka <[email protected]> Signed-off-by: Michal Hocko <[email protected]> --- Hi, Vlastimil has pointed out [1] that move_active_pages_to_lru is more confusing than necessary because we count two things, pgmoved and nr_moved. I believe that counting freed pages as PGDEACTIVATE is more confusing than helpful. I doubt that this patch will make any real difference in the real life but it at least makes the code easier which is a plus so I think this is more a cleanup than any bug fix. [1] http://lkml.kernel.org/r/[email protected] mm/vmscan.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index cf940af609fd..7e1c3cd91fab 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1878,7 +1878,6 @@ static unsigned move_active_pages_to_lru(struct lruvec *lruvec, enum lru_list lru) { struct pglist_data *pgdat = lruvec_pgdat(lruvec); - unsigned long pgmoved = 0; struct page *page; int nr_pages; int nr_moved = 0; @@ -1893,7 +1892,6 @@ static unsigned move_active_pages_to_lru(struct lruvec *lruvec, nr_pages = hpage_nr_pages(page); update_lru_size(lruvec, lru, page_zonenum(page), nr_pages); list_move(&page->lru, &lruvec->lists[lru]); - pgmoved += nr_pages; if (put_page_testzero(page)) { __ClearPageLRU(page); @@ -1913,7 +1911,7 @@ static unsigned move_active_pages_to_lru(struct lruvec *lruvec, } if (!is_active_lru(lru)) - __count_vm_events(PGDEACTIVATE, pgmoved); + __count_vm_events(PGDEACTIVATE, nr_moved); return nr_moved; } -- 2.11.0
