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Date: Tue, 22 Mar 2022 10:56:50 +0530
From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To: Yu Zhao <yuzhao@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andi Kleen <ak@...ux.intel.com>,
Catalin Marinas <catalin.marinas@....com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Hillf Danton <hdanton@...a.com>, Jens Axboe <axboe@...nel.dk>,
Jesse Barnes <jsbarnes@...gle.com>,
Johannes Weiner <hannes@...xchg.org>,
Jonathan Corbet <corbet@....net>,
Matthew Wilcox <willy@...radead.org>,
Mel Gorman <mgorman@...e.de>,
Michael Larabel <Michael@...haellarabel.com>,
Michal Hocko <mhocko@...nel.org>,
Mike Rapoport <rppt@...nel.org>,
Rik van Riel <riel@...riel.com>,
Vlastimil Babka <vbabka@...e.cz>,
Will Deacon <will@...nel.org>,
Ying Huang <ying.huang@...el.com>,
linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
page-reclaim@...gle.com, x86@...nel.org,
Yu Zhao <yuzhao@...gle.com>, Brian Geffon <bgeffon@...gle.com>,
Jan Alexander Steffens <heftig@...hlinux.org>,
Oleksandr Natalenko <oleksandr@...alenko.name>,
Steven Barrett <steven@...uorix.net>,
Suleiman Souhlal <suleiman@...gle.com>,
Daniel Byrne <djbyrne@....edu>,
Donald Carr <d@...os-reins.com>,
Holger Hoffstätte
<holger@...lied-asynchrony.com>,
Konstantin Kharlamov <Hi-Angel@...dex.ru>,
Shuang Zhai <szhai2@...rochester.edu>,
Sofia Trinh <sofia.trinh@....works>,
Vaibhav Jain <vaibhav@...ux.ibm.com>
Subject: Re: [PATCH v9 06/14] mm: multi-gen LRU: minimal implementation
Yu Zhao <yuzhao@...gle.com> writes:
+
> +static void inc_min_seq(struct lruvec *lruvec)
> +{
> + int type;
> + struct lru_gen_struct *lrugen = &lruvec->lrugen;
> +
> + VM_BUG_ON(!seq_is_valid(lruvec));
> +
> + for (type = 0; type < ANON_AND_FILE; type++) {
> + if (get_nr_gens(lruvec, type) != MAX_NR_GENS)
> + continue;
> +
> + reset_ctrl_pos(lruvec, type, true);
> + WRITE_ONCE(lrugen->min_seq[type], lrugen->min_seq[type] + 1);
> + }
> +}
> +
> +static bool try_to_inc_min_seq(struct lruvec *lruvec, bool can_swap)
> +{
> + int gen, type, zone;
> + bool success = false;
> + struct lru_gen_struct *lrugen = &lruvec->lrugen;
> + DEFINE_MIN_SEQ(lruvec);
> +
> + VM_BUG_ON(!seq_is_valid(lruvec));
> +
> + for (type = !can_swap; type < ANON_AND_FILE; type++) {
> + while (min_seq[type] + MIN_NR_GENS <= lrugen->max_seq) {
> + gen = lru_gen_from_seq(min_seq[type]);
> +
> + for (zone = 0; zone < MAX_NR_ZONES; zone++) {
> + if (!list_empty(&lrugen->lists[gen][type][zone]))
> + goto next;
> + }
> +
> + min_seq[type]++;
> + }
> +next:
> + ;
> + }
> +
> + /* see the comment on lru_gen_struct */
> + if (can_swap) {
> + min_seq[LRU_GEN_ANON] = min(min_seq[LRU_GEN_ANON], min_seq[LRU_GEN_FILE]);
> + min_seq[LRU_GEN_FILE] = max(min_seq[LRU_GEN_ANON], lrugen->min_seq[LRU_GEN_FILE]);
> + }
> +
> + for (type = !can_swap; type < ANON_AND_FILE; type++) {
> + if (min_seq[type] == lrugen->min_seq[type])
> + continue;
> +
> + reset_ctrl_pos(lruvec, type, true);
> + WRITE_ONCE(lrugen->min_seq[type], min_seq[type]);
> + success = true;
> + }
> +
> + return success;
> +}
> +
> +static void inc_max_seq(struct lruvec *lruvec, unsigned long max_seq)
> +{
> + int prev, next;
> + int type, zone;
> + struct lru_gen_struct *lrugen = &lruvec->lrugen;
> +
> + spin_lock_irq(&lruvec->lru_lock);
> +
> + VM_BUG_ON(!seq_is_valid(lruvec));
> +
> + if (max_seq != lrugen->max_seq)
> + goto unlock;
> +
> + inc_min_seq(lruvec);
Can this min seq update result in pages considered oldest become young.
ie, if we had seq value of 0 - 3 and we need ageing, the new min seq and
max_seq value will now become 1 - 4. What happens to pages in the
generation value 0 which was oldest generation earlier and is youngest
now.
> +
> + /* update the active/inactive LRU sizes for compatibility */
> + prev = lru_gen_from_seq(lrugen->max_seq - 1);
> + next = lru_gen_from_seq(lrugen->max_seq + 1);
> +
> + for (type = 0; type < ANON_AND_FILE; type++) {
> + for (zone = 0; zone < MAX_NR_ZONES; zone++) {
> + enum lru_list lru = type * LRU_INACTIVE_FILE;
> + long delta = lrugen->nr_pages[prev][type][zone] -
> + lrugen->nr_pages[next][type][zone];
> +
> + if (!delta)
> + continue;
> +
> + __update_lru_size(lruvec, lru, zone, delta);
> + __update_lru_size(lruvec, lru + LRU_ACTIVE, zone, -delta);
> + }
> + }
> +
> + for (type = 0; type < ANON_AND_FILE; type++)
> + reset_ctrl_pos(lruvec, type, false);
> +
> + /* make sure preceding modifications appear */
> + smp_store_release(&lrugen->max_seq, lrugen->max_seq + 1);
> +unlock:
> + spin_unlock_irq(&lruvec->lru_lock);
> +}
> +
....
+
> +static int evict_folios(struct lruvec *lruvec, struct scan_control *sc, int swappiness)
> +{
> + int type;
> + int scanned;
> + int reclaimed;
> + LIST_HEAD(list);
> + struct folio *folio;
> + enum vm_event_item item;
> + struct reclaim_stat stat;
> + struct mem_cgroup *memcg = lruvec_memcg(lruvec);
> + struct pglist_data *pgdat = lruvec_pgdat(lruvec);
> +
> + spin_lock_irq(&lruvec->lru_lock);
> +
> + scanned = isolate_folios(lruvec, sc, swappiness, &type, &list);
> +
> + if (try_to_inc_min_seq(lruvec, swappiness))
> + scanned++;
we are doing this before we shrink the page list. Any reason to do this before?
> +
> + if (get_nr_gens(lruvec, LRU_GEN_FILE) == MIN_NR_GENS)
> + scanned = 0;
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