From patchwork Tue Sep 26 04:09:36 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefan Roesch X-Patchwork-Id: 13398636 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7C46E81818 for ; Tue, 26 Sep 2023 04:10:01 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7BB306B018B; Tue, 26 Sep 2023 00:10:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 76B3F6B018C; Tue, 26 Sep 2023 00:10:01 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6326C6B018E; Tue, 26 Sep 2023 00:10:01 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 4E0E36B018B for ; Tue, 26 Sep 2023 00:10:01 -0400 (EDT) Received: from smtpin07.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 0FC3EC07A7 for ; Tue, 26 Sep 2023 04:10:01 +0000 (UTC) X-FDA: 81277420602.07.E13E8D0 Received: from 66-220-144-179.mail-mxout.facebook.com (66-220-144-179.mail-mxout.facebook.com [66.220.144.179]) by imf16.hostedemail.com (Postfix) with ESMTP id 6CA6C180006 for ; Tue, 26 Sep 2023 04:09:59 +0000 (UTC) Authentication-Results: imf16.hostedemail.com; dkim=none; spf=neutral (imf16.hostedemail.com: 66.220.144.179 is neither permitted nor denied by domain of shr@devkernel.io) smtp.mailfrom=shr@devkernel.io; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1695701399; 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; bh=wM4Sh7wNLr/HEbxi4LofFi4JD4PV8ZH53mZErVMmhPo=; b=7LguuAuWecUYkrr3nYF2SIpjisu6ls1LI+HduoAz5I/49QCm9z/RGbcaqpMgJKPb/2YMBr s8lg0qqDfkzYbQS9KJasKCb5yoIkRu8wLUP0FPjZIVbq1NtZSHFl8gpSwFRJyew7h3Eupe ivxa8Dv0vWcM0ZBuKzpft+Wcg4BLSG4= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1695701399; a=rsa-sha256; cv=none; b=uij9flJVd92jddS/djcYvebJYL1CrCisBQmWsGC/mgv77rECa5m0pT/IWmIstpIl8qkmj8 SzKY7XfEc8R1Tenf4OuPfZNdQ0tDRcWguX8Do7hw7QlENtYalR9YzbdpGVJQsKToM27Mgc X7NsAYWe7EFFX0GGppHGnjT+JGr5+8s= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=none; spf=neutral (imf16.hostedemail.com: 66.220.144.179 is neither permitted nor denied by domain of shr@devkernel.io) smtp.mailfrom=shr@devkernel.io; dmarc=none Received: by devbig1114.prn1.facebook.com (Postfix, from userid 425415) id 246DBC8F2417; Mon, 25 Sep 2023 21:09:43 -0700 (PDT) From: Stefan Roesch To: kernel-team@fb.com Cc: shr@devkernel.io, akpm@linux-foundation.org, david@redhat.com, hannes@cmpxchg.org, riel@surriel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v3 1/4] mm/ksm: add "smart" page scanning mode Date: Mon, 25 Sep 2023 21:09:36 -0700 Message-Id: <20230926040939.516161-2-shr@devkernel.io> X-Mailer: git-send-email 2.39.3 In-Reply-To: <20230926040939.516161-1-shr@devkernel.io> References: <20230926040939.516161-1-shr@devkernel.io> MIME-Version: 1.0 X-Rspamd-Queue-Id: 6CA6C180006 X-Rspam-User: X-Stat-Signature: sjk48m81j1tpc4pc6cce7dds6u3x99cx X-Rspamd-Server: rspam03 X-HE-Tag: 1695701399-301774 X-HE-Meta: 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 TDj99T93 WuFpzYXWQe5Ci7AAHPRpckINdOQ== 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: This change adds a "smart" page scanning mode for KSM. So far all the candidate pages are continuously scanned to find candidates for de-duplication. There are a considerably number of pages that cannot be de-duplicated. This is costly in terms of CPU. By using smart scanning considerable CPU savings can be achieved. This change takes the history of scanning pages into account and skips the page scanning of certain pages for a while if de-deduplication for this page has not been successful in the past. To do this it introduces two new fields in the ksm_rmap_item structure: age and remaining_skips. age, is the KSM age and remaining_skips determines how often scanning of this page is skipped. The age field is incremented each time the page is scanned and the page cannot be de- duplicated. age updated is capped at U8_MAX. How often a page is skipped is dependent how often de-duplication has been tried so far and the number of skips is currently limited to 8. This value has shown to be effective with different workloads. The feature is currently disable by default and can be enabled with the new smart_scan knob. The feature has shown to be very effective: upt to 25% of the page scans can be eliminated; the pages_to_scan rate can be reduced by 40 - 50% and a similar de-duplication rate can be maintained. Signed-off-by: Stefan Roesch Reviewed-by: David Hildenbrand --- mm/ksm.c | 103 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 103 insertions(+) diff --git a/mm/ksm.c b/mm/ksm.c index 981af9c72e7a..d65eb48f9a13 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -56,6 +56,8 @@ #define DO_NUMA(x) do { } while (0) #endif +typedef u8 rmap_age_t; + /** * DOC: Overview * @@ -193,6 +195,8 @@ struct ksm_stable_node { * @node: rb node of this rmap_item in the unstable tree * @head: pointer to stable_node heading this list in the stable tree * @hlist: link into hlist of rmap_items hanging off that stable_node + * @age: number of scan iterations since creation + * @remaining_skips: how many scans to skip */ struct ksm_rmap_item { struct ksm_rmap_item *rmap_list; @@ -205,6 +209,8 @@ struct ksm_rmap_item { struct mm_struct *mm; unsigned long address; /* + low bits used for flags below */ unsigned int oldchecksum; /* when unstable */ + rmap_age_t age; + rmap_age_t remaining_skips; union { struct rb_node node; /* when node of unstable tree */ struct { /* when listed from stable tree */ @@ -281,6 +287,9 @@ 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; +/* Skip pages that couldn't be de-duplicated previously */ +static bool ksm_smart_scan; + /* The number of zero pages which is placed by KSM */ unsigned long ksm_zero_pages; @@ -2305,6 +2314,73 @@ static struct ksm_rmap_item *get_next_rmap_item(struct ksm_mm_slot *mm_slot, return rmap_item; } +/* + * Calculate skip age for the ksm page age. The age determines how often + * de-duplicating has already been tried unsuccessfully. If the age is + * smaller, the scanning of this page is skipped for less scans. + * + * @age: rmap_item age of page + */ +static unsigned int skip_age(rmap_age_t age) +{ + if (age <= 3) + return 1; + if (age <= 5) + return 2; + if (age <= 8) + return 4; + + return 8; +} + +/* + * Determines if a page should be skipped for the current scan. + * + * @page: page to check + * @rmap_item: associated rmap_item of page + */ +static bool should_skip_rmap_item(struct page *page, + struct ksm_rmap_item *rmap_item) +{ + rmap_age_t age; + + if (!ksm_smart_scan) + return false; + + /* + * Never skip pages that are already KSM; pages cmp_and_merge_page() + * will essentially ignore them, but we still have to process them + * properly. + */ + if (PageKsm(page)) + return false; + + age = rmap_item->age; + if (age != U8_MAX) + rmap_item->age++; + + /* + * Smaller ages are not skipped, they need to get a chance to go + * through the different phases of the KSM merging. + */ + if (age < 3) + return false; + + /* + * Are we still allowed to skip? If not, then don't skip it + * and determine how much more often we are allowed to skip next. + */ + if (!rmap_item->remaining_skips) { + rmap_item->remaining_skips = skip_age(age); + return false; + } + + /* Skip this page */ + rmap_item->remaining_skips--; + remove_rmap_item_from_tree(rmap_item); + return true; +} + static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page) { struct mm_struct *mm; @@ -2409,6 +2485,10 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(struct page **page) if (rmap_item) { ksm_scan.rmap_list = &rmap_item->rmap_list; + + if (should_skip_rmap_item(*page, rmap_item)) + goto next_page; + ksm_scan.address += PAGE_SIZE; } else put_page(*page); @@ -3449,6 +3529,28 @@ static ssize_t full_scans_show(struct kobject *kobj, } KSM_ATTR_RO(full_scans); +static ssize_t smart_scan_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sysfs_emit(buf, "%u\n", ksm_smart_scan); +} + +static ssize_t smart_scan_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + int err; + bool value; + + err = kstrtobool(buf, &value); + if (err) + return -EINVAL; + + ksm_smart_scan = value; + return count; +} +KSM_ATTR(smart_scan); + static struct attribute *ksm_attrs[] = { &sleep_millisecs_attr.attr, &pages_to_scan_attr.attr, @@ -3469,6 +3571,7 @@ static struct attribute *ksm_attrs[] = { &stable_node_chains_prune_millisecs_attr.attr, &use_zero_pages_attr.attr, &general_profit_attr.attr, + &smart_scan_attr.attr, NULL, };