From nobody Sat Jan 3 03:54:03 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 E72D6E7C4EC for ; Wed, 4 Oct 2023 19:07:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245426AbjJDTHp (ORCPT ); Wed, 4 Oct 2023 15:07:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33096 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343886AbjJDTHY (ORCPT ); Wed, 4 Oct 2023 15:07:24 -0400 Received: from 66-220-144-179.mail-mxout.facebook.com (66-220-144-179.mail-mxout.facebook.com [66.220.144.179]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C183B173F for ; Wed, 4 Oct 2023 12:03:15 -0700 (PDT) Received: by devbig1114.prn1.facebook.com (Postfix, from userid 425415) id 70FD2D08BFFB; Wed, 4 Oct 2023 12:03:02 -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 v1 1/4] mm/ksm: add ksm advisor Date: Wed, 4 Oct 2023 12:02:46 -0700 Message-Id: <20231004190249.829015-2-shr@devkernel.io> X-Mailer: git-send-email 2.39.3 In-Reply-To: <20231004190249.829015-1-shr@devkernel.io> References: <20231004190249.829015-1-shr@devkernel.io> 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" This adds the ksm advisor. The ksm advisor automatically manages the pages_to_scan setting to achieve a target scan time. The target scan time defines how many seconds it should take to scan all the candidate KSM pages. In other words the pages_to_scan rate is changed by the advisor to achieve the target scan time. The algorithm has a max and min value to: - guarantee responsiveness to changes - to avoid to spend too much CPU The respective parameters are: - ksm_advisor_target_scan_time (how many seconds a scan should take) - ksm_advisor_min_pages (minimum value for pages_to_scan per batch) - ksm_advisor_max_pages (maximum valoe for pages_to_scan per batch) The algorithm calculates the change value based on the target scan time and the previous scan time. To avoid pertubations an exponentially weighted moving average is applied. By default the advisor is disabled. Currently there are two advisors: none and scan_time. Tests with various workloads have shown considerable CPU savings. Most of the workloads I have investigated have more candidate pages during startup, once the workload is stable in terms of memory, the number of candidate pages is reduced. Without the advisor, the pages_to_scan needs to be sized for the maximum number of candidate pages. So having this advisor definitely helps in reducing CPU consumption. For the instagram workload, the advisor achieves a 25% CPU reduction. Once the memory is stable, the pages_to_scan parameter gets reduced to about 40% of its max value. Signed-off-by: Stefan Roesch --- mm/ksm.c | 132 ++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 131 insertions(+), 1 deletion(-) diff --git a/mm/ksm.c b/mm/ksm.c index 7efcc68ccc6e..c9edfb293024 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -248,6 +248,9 @@ static struct kmem_cache *rmap_item_cache; static struct kmem_cache *stable_node_cache; static struct kmem_cache *mm_slot_cache; =20 +/* Default number of pages to scan per batch */ +#define DEFAULT_PAGES_TO_SCAN 100 + /* The number of pages scanned */ static unsigned long ksm_pages_scanned; =20 @@ -276,7 +279,7 @@ static unsigned int ksm_stable_node_chains_prune_millis= ecs =3D 2000; static int ksm_max_page_sharing =3D 256; =20 /* Number of pages ksmd should scan in one batch */ -static unsigned int ksm_thread_pages_to_scan =3D 100; +static unsigned int ksm_thread_pages_to_scan =3D DEFAULT_PAGES_TO_SCAN; =20 /* Milliseconds ksmd should sleep between batches */ static unsigned int ksm_thread_sleep_millisecs =3D 20; @@ -297,6 +300,129 @@ unsigned long ksm_zero_pages; /* The number of pages that have been skipped due to "smart scanning" */ static unsigned long ksm_pages_skipped; =20 +/* At least scan this many pages per batch. */ +static unsigned long ksm_advisor_min_pages =3D 500; + +/* Don't scan more than max pages per batch. */ +static unsigned long ksm_advisor_max_pages =3D 5000; + +/* Target scan time in seconds to analyze all KSM candidate pages. */ +static unsigned long ksm_advisor_target_scan_time =3D 200; + +/* Exponentially weighted moving average. */ +#define EWMA_WEIGHT 50 + +/** + * struct advisor_ctx - metadata for KSM advisor + * @start_scan: start time of the current scan + * @scan_time: scan time of previous scan + * @change: change in percent to pages_to_scan parameter + */ +struct advisor_ctx { + ktime_t start_scan; + s64 scan_time; + unsigned long change; +}; +static struct advisor_ctx advisor_ctx; + +/* Define different advisor's */ +enum ksm_advisor_type { + KSM_ADVISOR_NONE, + KSM_ADVISOR_FIRST =3D KSM_ADVISOR_NONE, + KSM_ADVISOR_SCAN_TIME, + KSM_ADVISOR_LAST =3D KSM_ADVISOR_SCAN_TIME +}; +static enum ksm_advisor_type ksm_advisor; + +static void init_advisor(void) +{ + advisor_ctx.start_scan =3D 0; + advisor_ctx.scan_time =3D 0; + advisor_ctx.change =3D 0; +} + +/* + * Use previous scan time if available, otherwise use current scan time as= an + * approximation for the previous scan time. + */ +static inline s64 prev_scan_time(struct advisor_ctx *ctx, s64 new_scan_tim= e) +{ + return ctx->scan_time ? ctx->scan_time : new_scan_time; +} + +/* Calculate exponential weighted moving average */ +static unsigned long ewma(unsigned long prev, unsigned long curr) +{ + return ((100 - EWMA_WEIGHT) * prev + EWMA_WEIGHT * curr) / 100; +} + +/* + * The scan time advisor is based on the current scan rate and the target + * scan rate. + * + * new_pages_to_scan =3D pages_to_scan * (scan_time / target_scan_tim= e) + * + * To avoid pertubations it calculates a change factor of previous changes. + * A new change factor is calculated for each iteration and it uses an + * exponentially weighted moving average. The new pages_to_scan value is + * multiplied with that change factor: + * + * new_pages_to_scan *=3D change facor + * + * In addition the new pages_to_scan value is capped by the max and min + * limits. + */ +static void scan_time_advisor(s64 scan_time) +{ + unsigned long pages; + unsigned long factor; + unsigned long change; + unsigned long last_scan_time; + + pages =3D ksm_thread_pages_to_scan; + last_scan_time =3D prev_scan_time(&advisor_ctx, scan_time); + + /* Calculate scan time as percentage of target scan time */ + factor =3D ksm_advisor_target_scan_time * 100 / scan_time; + factor =3D factor ? factor : 1; + + /* + * Calculate scan time as percentage of last scan time and use + * exponentially weighted average to smooth it + */ + change =3D scan_time * 100 / last_scan_time; + change =3D change ? change : 1; + change =3D ewma(advisor_ctx.change, change); + + /* Calculate new scan rate based on target scan rate. */ + pages =3D pages * 100 / factor; + /* Update pages_to_scan by weighted change percentage. */ + pages =3D pages * change / 100; + + /* Cap new pages_to_scan value */ + pages =3D max(pages, ksm_advisor_min_pages); + pages =3D min(pages, ksm_advisor_max_pages); + + /* Update advisor context */ + advisor_ctx.change =3D change; + advisor_ctx.scan_time =3D scan_time; + ksm_thread_pages_to_scan =3D pages; +} + +static void run_advisor(void) +{ + if (ksm_advisor =3D=3D KSM_ADVISOR_SCAN_TIME) { + s64 scan_time; + + /* Convert scan time to seconds */ + scan_time =3D ktime_ms_delta(ktime_get(), advisor_ctx.start_scan); + scan_time /=3D MSEC_PER_SEC; + scan_time =3D scan_time ? scan_time : 1; + + scan_time_advisor(scan_time); + } +} + #ifdef CONFIG_NUMA /* Zeroed when merging across nodes is not allowed */ static unsigned int ksm_merge_across_nodes =3D 1; @@ -2401,6 +2527,7 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(= struct page **page) =20 mm_slot =3D ksm_scan.mm_slot; if (mm_slot =3D=3D &ksm_mm_head) { + advisor_ctx.start_scan =3D ktime_get(); trace_ksm_start_scan(ksm_scan.seqnr, ksm_rmap_items); =20 /* @@ -2558,6 +2685,8 @@ static struct ksm_rmap_item *scan_get_next_rmap_item(= struct page **page) if (mm_slot !=3D &ksm_mm_head) goto next_mm; =20 + run_advisor(); + trace_ksm_stop_scan(ksm_scan.seqnr, ksm_rmap_items); ksm_scan.seqnr++; return NULL; @@ -3603,6 +3732,7 @@ 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; + init_advisor(); =20 err =3D ksm_slab_init(); if (err) --=20 2.39.3 From nobody Sat Jan 3 03:54:03 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 57881E7C4E9 for ; Wed, 4 Oct 2023 19:07:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245400AbjJDTHn (ORCPT ); Wed, 4 Oct 2023 15:07:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40046 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343888AbjJDTHY (ORCPT ); Wed, 4 Oct 2023 15:07:24 -0400 Received: from 66-220-144-178.mail-mxout.facebook.com (66-220-144-178.mail-mxout.facebook.com [66.220.144.178]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F370430ED for ; Wed, 4 Oct 2023 12:03:15 -0700 (PDT) Received: by devbig1114.prn1.facebook.com (Postfix, from userid 425415) id B20EFD08BFFD; Wed, 4 Oct 2023 12:03:02 -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 v1 2/4] mm/ksm: add sysfs knobs for advisor Date: Wed, 4 Oct 2023 12:02:47 -0700 Message-Id: <20231004190249.829015-3-shr@devkernel.io> X-Mailer: git-send-email 2.39.3 In-Reply-To: <20231004190249.829015-1-shr@devkernel.io> References: <20231004190249.829015-1-shr@devkernel.io> 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" This adds four new knobs for the KSM advisor to influence its behaviour. The knobs are: - advisor_mode: 0: no advisor (default) 1: scan time advisor - advisor_min_pages: 500 (default) - advisor_max_pages: 5000 (default) - advisor_target_scan_time: 200 (default in seconds) The new values will take effect on the next scan round. Signed-off-by: Stefan Roesch --- mm/ksm.c | 108 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 108 insertions(+) diff --git a/mm/ksm.c b/mm/ksm.c index c9edfb293024..12e70f806b2b 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -341,6 +341,14 @@ static void init_advisor(void) advisor_ctx.change =3D 0; } =20 +static void set_advisor_defaults(void) +{ + if (ksm_advisor =3D=3D KSM_ADVISOR_NONE) + ksm_thread_pages_to_scan =3D DEFAULT_PAGES_TO_SCAN; + else if (ksm_advisor =3D=3D KSM_ADVISOR_SCAN_TIME) + ksm_thread_pages_to_scan =3D ksm_advisor_min_pages; +} + /* * Use previous scan time if available, otherwise use current scan time as= an * approximation for the previous scan time. @@ -3692,6 +3700,102 @@ static ssize_t smart_scan_store(struct kobject *kob= j, } KSM_ATTR(smart_scan); =20 +static ssize_t advisor_mode_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sysfs_emit(buf, "%u\n", ksm_advisor); +} + +static ssize_t advisor_mode_store(struct kobject *kobj, + struct kobj_attribute *attr, const char *buf, + size_t count) +{ + unsigned int mode; + int err; + + err =3D kstrtouint(buf, 10, &mode); + if (err) + return -EINVAL; + if (mode > KSM_ADVISOR_LAST) + return -EINVAL; + + /* Set advisor default values */ + ksm_advisor =3D mode; + init_advisor(); + set_advisor_defaults(); + + return count; +} +KSM_ATTR(advisor_mode); + +static ssize_t advisor_min_pages_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sysfs_emit(buf, "%lu\n", ksm_advisor_min_pages); +} + +static ssize_t advisor_min_pages_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + int err; + unsigned long value; + + err =3D kstrtoul(buf, 10, &value); + if (err) + return -EINVAL; + + ksm_advisor_min_pages =3D value; + return count; +} +KSM_ATTR(advisor_min_pages); + +static ssize_t advisor_max_pages_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sysfs_emit(buf, "%lu\n", ksm_advisor_max_pages); +} + +static ssize_t advisor_max_pages_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + int err; + unsigned long value; + + err =3D kstrtoul(buf, 10, &value); + if (err) + return -EINVAL; + + ksm_advisor_max_pages =3D value; + return count; +} +KSM_ATTR(advisor_max_pages); + +static ssize_t advisor_target_scan_time_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + return sysfs_emit(buf, "%lu\n", ksm_advisor_target_scan_time); +} + +static ssize_t advisor_target_scan_time_store(struct kobject *kobj, + struct kobj_attribute *attr, + const char *buf, size_t count) +{ + int err; + unsigned long value; + + err =3D kstrtoul(buf, 10, &value); + if (err) + return -EINVAL; + if (value < 1) + return -EINVAL; + + ksm_advisor_target_scan_time =3D value; + return count; +} +KSM_ATTR(advisor_target_scan_time); + static struct attribute *ksm_attrs[] =3D { &sleep_millisecs_attr.attr, &pages_to_scan_attr.attr, @@ -3714,6 +3818,10 @@ static struct attribute *ksm_attrs[] =3D { &use_zero_pages_attr.attr, &general_profit_attr.attr, &smart_scan_attr.attr, + &advisor_mode_attr.attr, + &advisor_min_pages_attr.attr, + &advisor_max_pages_attr.attr, + &advisor_target_scan_time_attr.attr, NULL, }; =20 --=20 2.39.3 From nobody Sat Jan 3 03:54:03 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 F223FE7C4EC for ; Wed, 4 Oct 2023 19:07:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245438AbjJDTHu (ORCPT ); Wed, 4 Oct 2023 15:07:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33106 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343889AbjJDTHY (ORCPT ); Wed, 4 Oct 2023 15:07:24 -0400 Received: from 66-220-144-179.mail-mxout.facebook.com (66-220-144-179.mail-mxout.facebook.com [66.220.144.179]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C1F8430EA for ; Wed, 4 Oct 2023 12:03:15 -0700 (PDT) Received: by devbig1114.prn1.facebook.com (Postfix, from userid 425415) id 0521ED08C001; Wed, 4 Oct 2023 12:03:02 -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 v1 3/4] mm/ksm: add tracepoint for ksm advisor Date: Wed, 4 Oct 2023 12:02:48 -0700 Message-Id: <20231004190249.829015-4-shr@devkernel.io> X-Mailer: git-send-email 2.39.3 In-Reply-To: <20231004190249.829015-1-shr@devkernel.io> References: <20231004190249.829015-1-shr@devkernel.io> 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" This adds a new tracepoint for the ksm advisor. It reports the last scan time and the new setting of the pages_to_scan parameter. Signed-off-by: Stefan Roesch --- include/trace/events/ksm.h | 28 ++++++++++++++++++++++++++++ mm/ksm.c | 2 ++ 2 files changed, 30 insertions(+) diff --git a/include/trace/events/ksm.h b/include/trace/events/ksm.h index b5ac35c1d0e8..164133014922 100644 --- a/include/trace/events/ksm.h +++ b/include/trace/events/ksm.h @@ -245,6 +245,34 @@ TRACE_EVENT(ksm_remove_rmap_item, __entry->pfn, __entry->rmap_item, __entry->mm) ); =20 +/** + * ksm_advisor - called after the advisor has run + * + * @scan_time: scan time in seconds + * @pages_to_scan: new pages_to_scan value + * + * Allows to trace the ksm advisor. + */ +TRACE_EVENT(ksm_advisor, + + TP_PROTO(s64 scan_time, unsigned long pages_to_scan), + + TP_ARGS(scan_time, pages_to_scan), + + TP_STRUCT__entry( + __field(s64, scan_time) + __field(unsigned long, pages_to_scan) + ), + + TP_fast_assign( + __entry->scan_time =3D scan_time; + __entry->pages_to_scan =3D pages_to_scan; + ), + + TP_printk("ksm scan time %lld pages_to_scan %lu", + __entry->scan_time, __entry->pages_to_scan) +); + #endif /* _TRACE_KSM_H */ =20 /* This part must be outside protection */ diff --git a/mm/ksm.c b/mm/ksm.c index 12e70f806b2b..93dff974f6ea 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -415,6 +415,8 @@ static void scan_time_advisor(s64 scan_time) advisor_ctx.change =3D change; advisor_ctx.scan_time =3D scan_time; ksm_thread_pages_to_scan =3D pages; + + trace_ksm_advisor(scan_time, pages); } =20 static void run_advisor(void) --=20 2.39.3 From nobody Sat Jan 3 03:54:03 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 B1F1EE7C4E9 for ; Wed, 4 Oct 2023 19:07:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245486AbjJDTH4 (ORCPT ); Wed, 4 Oct 2023 15:07:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47496 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343901AbjJDTHZ (ORCPT ); Wed, 4 Oct 2023 15:07:25 -0400 Received: from 66-220-144-178.mail-mxout.facebook.com (66-220-144-178.mail-mxout.facebook.com [66.220.144.178]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7D7DF30F4 for ; Wed, 4 Oct 2023 12:03:19 -0700 (PDT) Received: by devbig1114.prn1.facebook.com (Postfix, from userid 425415) id 0F49CD08C004; Wed, 4 Oct 2023 12:03:03 -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 v1 4/4] mm/ksm: document ksm advisor and its sysfs knobs Date: Wed, 4 Oct 2023 12:02:49 -0700 Message-Id: <20231004190249.829015-5-shr@devkernel.io> X-Mailer: git-send-email 2.39.3 In-Reply-To: <20231004190249.829015-1-shr@devkernel.io> References: <20231004190249.829015-1-shr@devkernel.io> 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" This documents the KSM advisor and its new knobs in /sys/fs/kernel/mm. Signed-off-by: Stefan Roesch --- Documentation/admin-guide/mm/ksm.rst | 45 ++++++++++++++++++++++++++++ 1 file changed, 45 insertions(+) diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-gui= de/mm/ksm.rst index e59231ac6bb7..8de93650d3b0 100644 --- a/Documentation/admin-guide/mm/ksm.rst +++ b/Documentation/admin-guide/mm/ksm.rst @@ -164,6 +164,25 @@ smart_scan optimization is enabled. The ``pages_skipped`` metric shows how effective the setting is. =20 +advisor_mode + The ``advisor_mode`` selects the current advisor. Two modes are + supported: 0 (None) and 1 (Scan time). The default is None. By + setting ``advisor_mode`` to 1, the scan time advisor is enabled. + The section about ``advisor`` explains in detail how the scan time + advisor works. + +advisor_min_pages + specifies the lower limit of the ``pages_to_scan`` parameter of the + scan time advisor. The default is 500. + +adivsor_max_pages + specifies the upper limit of the ``pages_to_scan`` parameter of the + scan time advisor. The default is 5000. + +advisor_target_scan_time + specifies the target scan time in seconds to scan all the candidate + pages. The default value is 200 seconds. + The effectiveness of KSM and MADV_MERGEABLE is shown in ``/sys/kernel/mm/k= sm/``: =20 general_profit @@ -263,6 +282,32 @@ ksm_swpin_copy note that KSM page might be copied when swapping in because do_swap_page() cannot do all the locking needed to reconstitute a cross-anon_vma KSM pag= e. =20 +Advisor +=3D=3D=3D=3D=3D=3D=3D + +The number of candidate pages for KSM is dynamic. It can be often observed +that during the startup of an application more candidate pages need to be +processed. Without an advisor the ``pages_to_scan`` parameter needs to be +sized for the maximum number of candidate pages. The scan time advisor can +changes the ``pages_to_scan`` parameter based on demand. + +The advisor can be enabled so KSM can automatically adapt to changes in the +number of candidate pages to scan. Two advisors are implemented: 0 (None) = and +1 (Scan time). With None no advisor is enabled. The default is None. + +The Scan time advisor changes the ``pages_to_scan`` parameter based on the +observed scan times. The possible values for the ``pages_to_scan`` paramet= er is +limited by the ``advisor_min_pages`` and ``advisor_max_pages`` parameters.= In +addition there is also the ``advisor_target_scan_time`` parameter. This +parameter sets the target time to scan all the KSM candidate pages. The +parameter ``advisor_target_scan_time`` decides how aggressive the scan time +advisor scans candidate pages. Lower values make the scan time advisor to = scan +more aggresively. This is the most important parameter for the configurati= on of +the scan time advisor. + +The ``pages_to_scan`` parameter is re-calculated after a scan has been com= pleted. + + -- Izik Eidus, Hugh Dickins, 17 Nov 2009 --=20 2.39.3