mm/vmscan.c: do not allocate duplicate stack variables in shrink_page_list()

On path shrink_inactive_list() ---> shrink_page_list() we allocate stack
variables for the statistics twice.  This is completely useless, and
this just consumes stack much more, then we really need.

The patch kills duplicate stack variables from shrink_page_list(), and
this reduce stack usage and object file size significantly:

Stack usage:
  Before: vmscan.c:1122:22:shrink_page_list	648	static
  After:  vmscan.c:1122:22:shrink_page_list	616	static

Size of vmscan.o:
           text	   data	    bss	    dec	    hex	filename
  Before: 56866	   4720	    128	  61714	   f112	mm/vmscan.o
  After:  56770	   4720	    128	  61618	   f0b2	mm/vmscan.o

Link: http://lkml.kernel.org/r/154894900030.5211.12104993874109647641.stgit@localhost.localdomain
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 07a68dc..209c2c7 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1106,16 +1106,9 @@ static unsigned long shrink_page_list(struct list_head *page_list,
 {
        LIST_HEAD(ret_pages);
        LIST_HEAD(free_pages);
-       int pgactivate = 0;
-       unsigned nr_unqueued_dirty = 0;
-       unsigned nr_dirty = 0;
-       unsigned nr_congested = 0;
        unsigned nr_reclaimed = 0;
-       unsigned nr_writeback = 0;
-       unsigned nr_immediate = 0;
-       unsigned nr_ref_keep = 0;
-       unsigned nr_unmap_fail = 0;
 
+       memset(stat, 0, sizeof(*stat));
        cond_resched();
 
        while (!list_empty(page_list)) {
@@ -1159,10 +1152,10 @@ static unsigned long shrink_page_list(struct list_head *page_list,
                 */
                page_check_dirty_writeback(page, &dirty, &writeback);
                if (dirty || writeback)
-                       nr_dirty++;
+                       stat->nr_dirty++;
 
                if (dirty && !writeback)
-                       nr_unqueued_dirty++;
+                       stat->nr_unqueued_dirty++;
 
                /*
                 * Treat this page as congested if the underlying BDI is or if
@@ -1174,7 +1167,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
                if (((dirty || writeback) && mapping &&
                     inode_write_congested(mapping->host)) ||
                    (writeback && PageReclaim(page)))
-                       nr_congested++;
+                       stat->nr_congested++;
 
                /*
                 * If a page at the tail of the LRU is under writeback, there
@@ -1223,7 +1216,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
                        if (current_is_kswapd() &&
                            PageReclaim(page) &&
                            test_bit(PGDAT_WRITEBACK, &pgdat->flags)) {
-                               nr_immediate++;
+                               stat->nr_immediate++;
                                goto activate_locked;
 
                        /* Case 2 above */
@@ -1241,7 +1234,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
                                 * and it's also appropriate in global reclaim.
                                 */
                                SetPageReclaim(page);
-                               nr_writeback++;
+                               stat->nr_writeback++;
                                goto activate_locked;
 
                        /* Case 3 above */
@@ -1261,7 +1254,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
                case PAGEREF_ACTIVATE:
                        goto activate_locked;
                case PAGEREF_KEEP:
-                       nr_ref_keep++;
+                       stat->nr_ref_keep++;
                        goto keep_locked;
                case PAGEREF_RECLAIM:
                case PAGEREF_RECLAIM_CLEAN:
@@ -1326,7 +1319,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
                        if (unlikely(PageTransHuge(page)))
                                flags |= TTU_SPLIT_HUGE_PMD;
                        if (!try_to_unmap(page, flags)) {
-                               nr_unmap_fail++;
+                               stat->nr_unmap_fail++;
                                goto activate_locked;
                        }
                }
@@ -1474,7 +1467,7 @@ activate_locked:
                VM_BUG_ON_PAGE(PageActive(page), page);
                if (!PageMlocked(page)) {
                        SetPageActive(page);
-                       pgactivate++;
+                       stat->nr_activate++;
                        count_memcg_page_event(page, PGACTIVATE);
                }
 keep_locked:
@@ -1489,18 +1482,8 @@ keep:
        free_unref_page_list(&free_pages);
 
        list_splice(&ret_pages, page_list);
-       count_vm_events(PGACTIVATE, pgactivate);
-
-       if (stat) {
-               stat->nr_dirty = nr_dirty;
-               stat->nr_congested = nr_congested;
-               stat->nr_unqueued_dirty = nr_unqueued_dirty;
-               stat->nr_writeback = nr_writeback;
-               stat->nr_immediate = nr_immediate;
-               stat->nr_activate = pgactivate;
-               stat->nr_ref_keep = nr_ref_keep;
-               stat->nr_unmap_fail = nr_unmap_fail;
-       }
+       count_vm_events(PGACTIVATE, stat->nr_activate);
+
        return nr_reclaimed;
 }
 
@@ -1512,6 +1495,7 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
                .priority = DEF_PRIORITY,
                .may_unmap = 1,
        };
+       struct reclaim_stat dummy_stat;
        unsigned long ret;
        struct page *page, *next;
        LIST_HEAD(clean_pages);
@@ -1525,7 +1509,7 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
        }
 
        ret = shrink_page_list(&clean_pages, zone->zone_pgdat, &sc,
-                       TTU_IGNORE_ACCESS, NULL, true);
+                       TTU_IGNORE_ACCESS, &dummy_stat, true);
        list_splice(&clean_pages, page_list);
        mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, -ret);
        return ret;
@@ -1900,7 +1884,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
        unsigned long nr_scanned;
        unsigned long nr_reclaimed = 0;
        unsigned long nr_taken;
-       struct reclaim_stat stat = {};
+       struct reclaim_stat stat;
        int file = is_file_lru(lru);
        struct pglist_data *pgdat = lruvec_pgdat(lruvec);
        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;