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This is to pave the way for subsequent real optimization features. Use it by: echo 8 > /sys/kernel/mm/ksm/run Signed-off-by: xu xin Signed-off-by: CGEL --- mm/ksm.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/mm/ksm.c b/mm/ksm.c index 2f315c69fa2c..c80d908221a4 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -290,6 +290,7 @@ static int ksm_nr_node_ids =3D 1; #define KSM_RUN_MERGE 1 #define KSM_RUN_UNMERGE 2 #define KSM_RUN_OFFLINE 4 +#define KSM_RUN_AUTO 8 static unsigned long ksm_run =3D KSM_RUN_STOP; static void wait_while_offlining(void); =20 @@ -2416,7 +2417,9 @@ static void ksm_do_scan(unsigned int scan_npages) =20 static int ksmd_should_run(void) { - return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list); + if (!list_empty(&ksm_mm_head.mm_list)) + return ksm_run & KSM_RUN_AUTO || ksm_run & KSM_RUN_MERGE; + return 0; } =20 static int ksm_scan_thread(void *nothing) @@ -2916,7 +2919,7 @@ static ssize_t run_store(struct kobject *kobj, struct= kobj_attribute *attr, err =3D kstrtouint(buf, 10, &flags); if (err) return -EINVAL; - if (flags > KSM_RUN_UNMERGE) + if (flags > KSM_RUN_UNMERGE && flags !=3D KSM_RUN_AUTO) return -EINVAL; =20 /* @@ -2942,7 +2945,7 @@ static ssize_t run_store(struct kobject *kobj, struct= kobj_attribute *attr, } mutex_unlock(&ksm_thread_mutex); =20 - if (flags & KSM_RUN_MERGE) + if (flags & KSM_RUN_MERGE || flags & KSM_RUN_AUTO) wake_up_interruptible(&ksm_thread_wait); =20 return count; --=20 2.25.1 From nobody Sun Apr 12 00:55:48 2026 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 10F70C19F28 for ; Wed, 3 Aug 2022 10:05:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237674AbiHCKFl (ORCPT ); Wed, 3 Aug 2022 06:05:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48038 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236217AbiHCKFh (ORCPT ); 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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 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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 no= de) + * @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; }; =20 /** @@ -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; =20 +/* + * Work in auto-mode. + * Maximum number of multiplicative factor of pages_to_scan. + */ +static unsigned int ksm_max_scanning_factor =3D 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 =3D 1; + #ifdef CONFIG_NUMA /* Zeroed when merging across nodes is not allowed */ static unsigned int ksm_merge_across_nodes =3D 1; @@ -2031,6 +2048,8 @@ static void stable_tree_append(struct rmap_item *rmap= _item, rmap_item->address |=3D STABLE_FLAG; hlist_add_head(&rmap_item->hlist, &stable_node->hlist); =20 + 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(str= uct page **page) return NULL; } =20 +/* + * 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 =3D scanning_factor << 1; + if (scanning_factor > ksm_max_scanning_factor) + scanning_factor =3D ksm_max_scanning_factor; +} + +static inline void reset_scanning_factor(void) +{ + scanning_factor =3D 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); =20 + /* + * 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 =3D 0; + } + try_to_freeze(); =20 if (ksmd_should_run()) { @@ -2952,6 +3009,32 @@ static ssize_t run_store(struct kobject *kobj, struc= t kobj_attribute *attr, } KSM_ATTR(run); =20 +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 =3D kstrtouint(buf, 10, &value); + if (err) + return -EINVAL; + + if (value < 1) + return -EINVAL; + + ksm_max_scanning_factor =3D 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[] =3D { &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, --=20 2.25.1 From nobody Sun Apr 12 00:55:48 2026 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 53063C19F28 for ; Wed, 3 Aug 2022 10:06:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236251AbiHCKGA (ORCPT ); Wed, 3 Aug 2022 06:06:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48452 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237794AbiHCKFx (ORCPT ); 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Wed, 03 Aug 2022 03:05:50 -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 3/4] ksm: let ksmd work automatically with memory threshold Date: Wed, 3 Aug 2022 10:05:43 +0000 Message-Id: <20220803100543.1653550-1-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 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: xu xin When memory is sufficient, merging pages to save memory is not very much needed, and it also inceases delays of COW for user application. So set a memory threshold, when free memory is lower than the threshold, ksmd will be triggered to compare and merge pages. And to avoid ping-pong effect due to the threshold, ksmd needs to try to merge pages until free memory is larger than (threshold + total_memory * 1/16). Before free memory is lower than the threshold, ksmd will still scan pages at a very low speed, to calculate their checksum but not to compare and merge pages. | | ----(Threshold + total_memory/16)-------- | | ------Threshold------ | | | |_____ksmd try to merge pages__| We also add a new sysfs klob auto_threshold_percent for user to be able to tune. Signed-off-by: xu xin Signed-off-by: CGEL --- mm/ksm.c | 95 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 92 insertions(+), 3 deletions(-) diff --git a/mm/ksm.c b/mm/ksm.c index 8acc893e4d61..78819b56efec 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -294,6 +294,17 @@ static unsigned int ksm_max_scanning_factor =3D 32; */ static unsigned int scanning_factor =3D 1; =20 +/* + * Work in auto-mode. + * Default ksm_auto_threshold_percent: 20, means 20%. When free memory + * is lower than total memory * ksm_auto_threshold_percent/100, ksmd will + * be triggered to compare and merge pages. + */ +unsigned int ksm_auto_threshold_percent =3D 20; + +/* Work in auto-mode. Whether trigger ksmd to compare and merge pages */ +static bool auto_triggered; + #ifdef CONFIG_NUMA /* Zeroed when merging across nodes is not allowed */ static unsigned int ksm_merge_across_nodes =3D 1; @@ -2446,11 +2457,46 @@ static void ksm_do_scan(unsigned int scan_npages) rmap_item =3D scan_get_next_rmap_item(&page); if (!rmap_item) return; - cmp_and_merge_page(page, rmap_item); + if (ksm_run & KSM_RUN_AUTO && !auto_triggered) { + /* + * This should happens only when ksm_run is KSM_RUN_AUTO + * and free memory threshold still not reached. + * The reason to calculate it's checksum is to reduce the + * waiting time the rmap_item is added to unstable tree. + */ + rmap_item->oldchecksum =3D calc_checksum(page); + } else + cmp_and_merge_page(page, rmap_item); + put_page(page); } } =20 +/* Work in auto mode, should reset auto_triggered ? */ +static bool should_untrigger_ksmd_to_merge(void) +{ + unsigned long total_ram_pages, free_pages; + + total_ram_pages =3D totalram_pages(); + free_pages =3D global_zone_page_state(NR_FREE_PAGES); + + return free_pages > (total_ram_pages * + ksm_auto_threshold_percent / 100) + + (total_ram_pages >> 4); +} + +/* Work in auto mode, should ksmd start to merge ? */ +static bool should_trigger_ksmd_to_merge(void) +{ + unsigned long total_ram_pages, free_pages; + + total_ram_pages =3D totalram_pages(); + free_pages =3D global_zone_page_state(NR_FREE_PAGES); + + return free_pages < (total_ram_pages * + ksm_auto_threshold_percent / 100); +} + static int ksmd_should_run(void) { if (!list_empty(&ksm_mm_head.mm_list)) @@ -2469,8 +2515,18 @@ static int ksm_scan_thread(void *nothing) mutex_lock(&ksm_thread_mutex); wait_while_offlining(); if (ksmd_should_run()) { - if (ksm_run & KSM_RUN_AUTO) - ksm_do_scan(ksm_thread_pages_to_scan * scanning_factor); + if (ksm_run & KSM_RUN_AUTO) { + /* + * If free memory is not lower than threshold, we only scan + * 5 pages and just calculate pages' checksum and not compare + * and merge them. Otherwise, do real scanning and merging as + * scanning-enhanced algorithm. + */ + if (!auto_triggered) + ksm_do_scan(5); + else + ksm_do_scan(ksm_thread_pages_to_scan * scanning_factor); + } else ksm_do_scan(ksm_thread_pages_to_scan); } @@ -2491,6 +2547,11 @@ static int ksm_scan_thread(void *nothing) reset_scanning_factor(); =20 ksm_scan.new_ksmpages_of_this_scanning =3D 0; + + if (should_trigger_ksmd_to_merge()) + auto_triggered =3D true; + else if (should_untrigger_ksmd_to_merge()) + auto_triggered =3D false; } =20 try_to_freeze(); @@ -3035,6 +3096,32 @@ static ssize_t max_scanning_factor_store(struct kobj= ect *kobj, } KSM_ATTR(max_scanning_factor); =20 +static ssize_t auto_threshold_percent_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sysfs_emit(buf, "%u\n", ksm_auto_threshold_percent); +} + +static ssize_t auto_threshold_percent_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + unsigned int value; + int err; + + err =3D kstrtouint(buf, 10, &value); + if (err) + return -EINVAL; + + if (value > 100) + return -EINVAL; + + ksm_auto_threshold_percent =3D value; + + return count; +} +KSM_ATTR(auto_threshold_percent); + #ifdef CONFIG_NUMA static ssize_t merge_across_nodes_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) @@ -3246,6 +3333,7 @@ static struct attribute *ksm_attrs[] =3D { &pages_to_scan_attr.attr, &run_attr.attr, &max_scanning_factor_attr.attr, + &auto_threshold_percent_attr.attr, &pages_shared_attr.attr, &pages_sharing_attr.attr, &pages_unshared_attr.attr, @@ -3277,6 +3365,7 @@ static int __init ksm_init(void) zero_checksum =3D calc_checksum(ZERO_PAGE(0)); /* Default to false for backwards compatibility */ ksm_use_zero_pages =3D false; + auto_triggered =3D false; =20 err =3D ksm_slab_init(); if (err) --=20 2.25.1 From nobody Sun Apr 12 00:55:48 2026 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 13560C19F28 for ; 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Wed, 03 Aug 2022 03:06:04 -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 4/4] ksm: show ksmd status of auto mode Date: Wed, 3 Aug 2022 10:05:59 +0000 Message-Id: <20220803100559.1653604-1-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 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: xu xin Add a sysfs interface of ksmd_status to show some details related with auto-mode. Signed-off-by: xu xin Signed-off-by: CGEL --- mm/ksm.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/mm/ksm.c b/mm/ksm.c index 78819b56efec..6417bc034a3d 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -3070,6 +3070,29 @@ static ssize_t run_store(struct kobject *kobj, struc= t kobj_attribute *attr, } KSM_ATTR(run); =20 +static ssize_t ksmd_status_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + int len =3D 0; + + if (ksm_run & KSM_RUN_AUTO) { + len +=3D sysfs_emit_at(buf, len, "mode: auto\n"); + len +=3D sysfs_emit_at(buf, len, "auto_triggered %d\n", + auto_triggered); + len +=3D sysfs_emit_at(buf, len, "scanning_factor: %u\n", + scanning_factor); + } else if (ksm_run & KSM_RUN_MERGE) + len +=3D sysfs_emit_at(buf, len, "mode: on\n"); + else if (ksm_run & KSM_RUN_UNMERGE) + len +=3D sysfs_emit_at(buf, len, "mode: unmerge\n"); + else + len +=3D sysfs_emit_at(buf, len, "mode: off\n"); + + + return len; +} +KSM_ATTR_RO(ksmd_status); + static ssize_t max_scanning_factor_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) { @@ -3332,6 +3355,7 @@ static struct attribute *ksm_attrs[] =3D { &sleep_millisecs_attr.attr, &pages_to_scan_attr.attr, &run_attr.attr, + &ksmd_status_attr.attr, &max_scanning_factor_attr.attr, &auto_threshold_percent_attr.attr, &pages_shared_attr.attr, --=20 2.25.1