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SubjectRe: [PATCH] mm: Do not allocate duplicate stack variables in shrink_page_list()
On Thu 31-01-19 18:37:02, Kirill Tkhai wrote:
> 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:

significantly is a bit of an overstatement for 32B saved...

> 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>

Acked-by: Michal Hocko <mhocko@suse.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;
>

--
Michal Hocko
SUSE Labs

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