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Wed, 03 Aug 2022 03:05:35 -0700 (PDT) From: cgel.zte@gmail.com X-Google-Original-From: xu.xin16@zte.con.cn To: akpm@linux-foundation.org Cc: hughd@google.com, izik.eidus@ravellosystems.com, willy@infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, xu xin , CGEL Subject: [RFC PATCH 2/4] ksm: implement scan-enhanced algorithm of auto mode Date: Wed, 3 Aug 2022 10:05:30 +0000 Message-Id: <20220803100530.1653496-1-xu.xin16@zte.con.cn> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220803100306.1653382-1-xu.xin16@zte.con.cn> References: <20220803100306.1653382-1-xu.xin16@zte.con.cn> MIME-Version: 1.0 ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1659521137; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=C9VGA9sPog0r28l3bCbEGjn4o1fpHQlIN2nhYVLWw/k=; 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dmarc=pass (policy=none) header.from=gmail.com X-Stat-Signature: qow4upure796wwob5q9ftgba4tzrp7ek X-Rspamd-Queue-Id: 436D7140128 X-Rspamd-Server: rspam10 X-HE-Tag: 1659521136-536576 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: xu xin Implement the scan-enhanced algorithm of auto mode. In this algorithm, after every time of scanning, if new ksm pages are obtained, it will double pages_to_scan for the next scanning until the general multiplying factor is not less than max_scanning_factor. If no new ksm pages are obtained, then reset pages_to_scan to the default value. We add the sysfs klob of max_scanning_factor to limit scanning factor's excessive growth. Signed-off-by: CGEL Signed-off-by: xu xin --- mm/ksm.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 86 insertions(+), 2 deletions(-) diff --git a/mm/ksm.c b/mm/ksm.c index c80d908221a4..8acc893e4d61 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -131,6 +131,8 @@ struct mm_slot { * @address: the next address inside that to be scanned * @rmap_list: link to the next rmap to be scanned in the rmap_list * @seqnr: count of completed full scans (needed when removing unstable node) + * @new_ksmpages_of_this_scanning: count of the new merged KSM pages in the + * current scanning of mm_lists (cleared after ksm_do_scan() ends) * * There is only the one ksm_scan instance of this cursor structure. */ @@ -139,6 +141,7 @@ struct ksm_scan { unsigned long address; struct rmap_item **rmap_list; unsigned long seqnr; + unsigned long new_ksmpages_of_this_scanning; }; /** @@ -277,6 +280,20 @@ static unsigned int zero_checksum __read_mostly; /* Whether to merge empty (zeroed) pages with actual zero pages */ static bool ksm_use_zero_pages __read_mostly; +/* + * Work in auto-mode. + * Maximum number of multiplicative factor of pages_to_scan. + */ +static unsigned int ksm_max_scanning_factor = 32; + +/* + * Work in auto-mode. + * The multiplicative factor of pages_to_scan. + * Real pages to scan equals to the product of scanning_factor + * and pages_to_scan + */ +static unsigned int scanning_factor = 1; + #ifdef CONFIG_NUMA /* Zeroed when merging across nodes is not allowed */ static unsigned int ksm_merge_across_nodes = 1; @@ -2031,6 +2048,8 @@ static void stable_tree_append(struct rmap_item *rmap_item, rmap_item->address |= STABLE_FLAG; hlist_add_head(&rmap_item->hlist, &stable_node->hlist); + ksm_scan.new_ksmpages_of_this_scanning++; + if (rmap_item->hlist.next) ksm_pages_sharing++; else @@ -2396,6 +2415,23 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page) return NULL; } +/* + * enhance_scanning_factor(): + * double the values of scanning_factor, but not more than + * ksm_max_scanning_factor. + */ +static inline void enhance_scanning_factor(void) +{ + scanning_factor = scanning_factor << 1; + if (scanning_factor > ksm_max_scanning_factor) + scanning_factor = ksm_max_scanning_factor; +} + +static inline void reset_scanning_factor(void) +{ + scanning_factor = 1; +} + /** * ksm_do_scan - the ksm scanner main worker function. * @scan_npages: number of pages we want to scan before we return. @@ -2432,10 +2468,31 @@ static int ksm_scan_thread(void *nothing) while (!kthread_should_stop()) { mutex_lock(&ksm_thread_mutex); wait_while_offlining(); - if (ksmd_should_run()) - ksm_do_scan(ksm_thread_pages_to_scan); + if (ksmd_should_run()) { + if (ksm_run & KSM_RUN_AUTO) + ksm_do_scan(ksm_thread_pages_to_scan * scanning_factor); + else + ksm_do_scan(ksm_thread_pages_to_scan); + } mutex_unlock(&ksm_thread_mutex); + /* + * If there are new ksm pages after scanning, then we + * can enhance scanning_factor to improve ksm_thread's + * pages_to_scan to speed up scanning. Otherwaise, we + * reset scanning_factor to be one, so that to recover + * the normal state because there is greater probability + * of getting no new KsmPages in the next scanning. + */ + if (ksm_run & KSM_RUN_AUTO) { + if (ksm_scan.new_ksmpages_of_this_scanning > 0) + enhance_scanning_factor(); + else + reset_scanning_factor(); + + ksm_scan.new_ksmpages_of_this_scanning = 0; + } + try_to_freeze(); if (ksmd_should_run()) { @@ -2952,6 +3009,32 @@ static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr, } KSM_ATTR(run); +static ssize_t max_scanning_factor_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sysfs_emit(buf, "%u\n", ksm_max_scanning_factor); +} + +static ssize_t max_scanning_factor_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + unsigned int value; + int err; + + err = kstrtouint(buf, 10, &value); + if (err) + return -EINVAL; + + if (value < 1) + return -EINVAL; + + ksm_max_scanning_factor = value; + + return count; +} +KSM_ATTR(max_scanning_factor); + #ifdef CONFIG_NUMA static ssize_t merge_across_nodes_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) @@ -3162,6 +3245,7 @@ static struct attribute *ksm_attrs[] = { &sleep_millisecs_attr.attr, &pages_to_scan_attr.attr, &run_attr.attr, + &max_scanning_factor_attr.attr, &pages_shared_attr.attr, &pages_sharing_attr.attr, &pages_unshared_attr.attr,