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Subject[PATCH] mm: Do not allocate duplicate stack variables in shrink_page_list()
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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

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
mm/vmscan.c | 44 ++++++++++++++------------------------------
1 file changed, 14 insertions(+), 30 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index dd9554f5d788..54a389fd91e2 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1128,16 +1128,9 @@ 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)) {
@@ -1181,10 +1174,10 @@ 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
@@ -1196,7 +1189,7 @@ 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
@@ -1245,7 +1238,7 @@ 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 */
@@ -1263,7 +1256,7 @@ 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 */
@@ -1283,7 +1276,7 @@ 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:
@@ -1348,7 +1341,7 @@ 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;
}
}
@@ -1496,7 +1489,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
VM_BUG_ON_PAGE(PageActive(page), page);
if (!PageMlocked(page)) {
SetPageActive(page);
- pgactivate++;
+ stat->nr_activate++;
count_memcg_page_event(page, PGACTIVATE);
}
keep_locked:
@@ -1511,18 +1504,8 @@ static unsigned long shrink_page_list(struct list_head *page_list,
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;
}

@@ -1534,6 +1517,7 @@ 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);
@@ -1547,7 +1531,7 @@ 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;
@@ -1922,7 +1906,7 @@ 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;
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