On 01.02.2019 14:26, Michal Hocko wrote: > 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...
32/648*100 = 4.93827160493827160400 Almost 5%. I think it's not so bad... >> 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 <[email protected]> > > Acked-by: Michal Hocko <[email protected]> > >> --- >> 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; >> >
