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Date: Tue, 09 Apr 2013 16:41:36 +0800
From: Simon Jeons <simon.jeons@...il.com>
To: Joonsoo Kim <iamjoonsoo.kim@....com>
CC: Mel Gorman <mgorman@...e.de>, Linux-MM <linux-mm@...ck.org>,
Jiri Slaby <jslaby@...e.cz>,
Valdis Kletnieks <Valdis.Kletnieks@...edu>,
Rik van Riel <riel@...hat.com>,
Zlatko Calusic <zcalusic@...sync.net>,
Johannes Weiner <hannes@...xchg.org>,
dormando <dormando@...ia.net>,
Satoru Moriya <satoru.moriya@....com>,
Michal Hocko <mhocko@...e.cz>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/10] mm: vmscan: Have kswapd shrink slab only once per
priority
Hi Joonsoo,
On 04/09/2013 02:53 PM, Joonsoo Kim wrote:
> Hello, Mel.
> Sorry for too late question.
>
> On Sun, Mar 17, 2013 at 01:04:14PM +0000, Mel Gorman wrote:
>> If kswaps fails to make progress but continues to shrink slab then it'll
>> either discard all of slab or consume CPU uselessly scanning shrinkers.
>> This patch causes kswapd to only call the shrinkers once per priority.
>>
>> Signed-off-by: Mel Gorman <mgorman@...e.de>
>> ---
>> mm/vmscan.c | 28 +++++++++++++++++++++-------
>> 1 file changed, 21 insertions(+), 7 deletions(-)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 7d5a932..84375b2 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -2661,9 +2661,10 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
>> */
>> static bool kswapd_shrink_zone(struct zone *zone,
>> struct scan_control *sc,
>> - unsigned long lru_pages)
>> + unsigned long lru_pages,
>> + bool shrinking_slab)
>> {
>> - unsigned long nr_slab;
>> + unsigned long nr_slab = 0;
>> struct reclaim_state *reclaim_state = current->reclaim_state;
>> struct shrink_control shrink = {
>> .gfp_mask = sc->gfp_mask,
>> @@ -2673,9 +2674,15 @@ static bool kswapd_shrink_zone(struct zone *zone,
>> sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone));
>> shrink_zone(zone, sc);
>>
>> - reclaim_state->reclaimed_slab = 0;
>> - nr_slab = shrink_slab(&shrink, sc->nr_scanned, lru_pages);
>> - sc->nr_reclaimed += reclaim_state->reclaimed_slab;
>> + /*
>> + * Slabs are shrunk for each zone once per priority or if the zone
>> + * being balanced is otherwise unreclaimable
>> + */
>> + if (shrinking_slab || !zone_reclaimable(zone)) {
>> + reclaim_state->reclaimed_slab = 0;
>> + nr_slab = shrink_slab(&shrink, sc->nr_scanned, lru_pages);
>> + sc->nr_reclaimed += reclaim_state->reclaimed_slab;
>> + }
>>
>> if (nr_slab == 0 && !zone_reclaimable(zone))
>> zone->all_unreclaimable = 1;
> Why shrink_slab() is called here?
> I think that outside of zone loop is better place to run shrink_slab(),
> because shrink_slab() is not directly related to a specific zone.
True.
>
> And this is a question not related to this patch.
> Why nr_slab is used here to decide zone->all_unreclaimable?
> nr_slab is not directly related whether a specific zone is reclaimable
> or not, and, moreover, nr_slab is not directly related to number of
> reclaimed pages. It just say some objects in the system are freed.
>
> This question comes from my ignorance, so please enlighten me.
Good question, I also want to know. ;-)
>
> Thanks.
>
>> @@ -2713,6 +2720,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
>> int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
>> unsigned long nr_soft_reclaimed;
>> unsigned long nr_soft_scanned;
>> + bool shrinking_slab = true;
>> struct scan_control sc = {
>> .gfp_mask = GFP_KERNEL,
>> .priority = DEF_PRIORITY,
>> @@ -2861,7 +2869,8 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
>> * already being scanned that that high
>> * watermark would be met at 100% efficiency.
>> */
>> - if (kswapd_shrink_zone(zone, &sc, lru_pages))
>> + if (kswapd_shrink_zone(zone, &sc,
>> + lru_pages, shrinking_slab))
>> raise_priority = false;
>>
>> nr_to_reclaim += sc.nr_to_reclaim;
>> @@ -2900,6 +2909,9 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
>> pfmemalloc_watermark_ok(pgdat))
>> wake_up(&pgdat->pfmemalloc_wait);
>>
>> + /* Only shrink slab once per priority */
>> + shrinking_slab = false;
>> +
>> /*
>> * Fragmentation may mean that the system cannot be rebalanced
>> * for high-order allocations in all zones. If twice the
>> @@ -2925,8 +2937,10 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
>> * Raise priority if scanning rate is too low or there was no
>> * progress in reclaiming pages
>> */
>> - if (raise_priority || !this_reclaimed)
>> + if (raise_priority || !this_reclaimed) {
>> sc.priority--;
>> + shrinking_slab = true;
>> + }
>> } while (sc.priority >= 1 &&
>> !pgdat_balanced(pgdat, order, *classzone_idx));
>>
>> --
>> 1.8.1.4
>>
>> --
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> --
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