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Message-ID: <e61efd8b-2a27-d83f-0568-1d16e0321417@virtuozzo.com>
Date: Fri, 1 Feb 2019 14:59:10 +0300
From: Kirill Tkhai <ktkhai@...tuozzo.com>
To: Michal Hocko <mhocko@...nel.org>
Cc: akpm@...ux-foundation.org, hannes@...xchg.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Do not allocate duplicate stack variables in
shrink_page_list()
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 <ktkhai@...tuozzo.com>
>
> Acked-by: Michal Hocko <mhocko@...e.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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