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Date: Wed, 16 Jun 2021 15:49:52 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: "Chu,Kaiping" <chukaiping@...du.com>,
"mcgrof@...nel.org" <mcgrof@...nel.org>,
"keescook@...omium.org" <keescook@...omium.org>,
"yzaikin@...gle.com" <yzaikin@...gle.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"nigupta@...dia.com" <nigupta@...dia.com>,
"bhe@...hat.com" <bhe@...hat.com>,
"khalid.aziz@...cle.com" <khalid.aziz@...cle.com>,
"iamjoonsoo.kim@....com" <iamjoonsoo.kim@....com>,
"mateusznosek0@...il.com" <mateusznosek0@...il.com>,
"sh_def@....com" <sh_def@....com>,
Charan Teja Kalla <charante@...eaurora.org>,
David Rientjes <rientjes@...gle.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: 答复: [PATCH v4] mm/compaction: let proactive compaction order configurable
On 6/1/21 3:15 AM, Chu,Kaiping wrote:
>
>
>> -----邮件原件-----
>> 发件人: Vlastimil Babka <vbabka@...e.cz>
>> 发送时间: 2021年5月29日 1:42
>> 收件人: Chu,Kaiping <chukaiping@...du.com>; mcgrof@...nel.org;
>> keescook@...omium.org; yzaikin@...gle.com; akpm@...ux-foundation.org;
>> nigupta@...dia.com; bhe@...hat.com; khalid.aziz@...cle.com;
>> iamjoonsoo.kim@....com; mateusznosek0@...il.com; sh_def@....com
>> 抄送: linux-kernel@...r.kernel.org; linux-fsdevel@...r.kernel.org;
>> linux-mm@...ck.org
>> 主题: Re: [PATCH v4] mm/compaction: let proactive compaction order
>> configurable
>>
>> On 4/28/21 4:28 AM, chukaiping wrote:
>> > Currently the proactive compaction order is fixed to
>> > COMPACTION_HPAGE_ORDER(9), it's OK in most machines with lots of
>> > normal 4KB memory, but it's too high for the machines with small
>> > normal memory, for example the machines with most memory configured as
>> > 1GB hugetlbfs huge pages. In these machines the max order of free
>> > pages is often below 9, and it's always below 9 even with hard
>> > compaction. This will lead to proactive compaction be triggered very
>> > frequently.
>>
>> Could you be more concrete about "very frequently"? There's a
>> proactive_defer mechanism that should help here. Normally the proactive
>> compaction attempt happens each 500ms, but if it fails to improve the
>> fragmentation score, it defers for 32 seconds. So is 32 seconds still too
>> frequent? Or the score does improve thus defer doesn't happen, but the cost
>> of that improvement is too high compared to the amount of the
>> improvement?
> I didn't measure the frequency accurately, I only judge it from code. The defer of 32 seconds is still very short to us, we want the proactive compaction running period to be hours.
Hours sounds like a lot, and maybe something that would indeed be easier to
accomplies with userspace proactive compaction triggering [1] than any carefully
tuned thresholds.
But with that low frequency, doesn't the kswapd+kcompactd non-proactive
compaction actually happen more frequently? That one should react to the order
that the allocation waking up kswapd requested, AFAIK.
[1] https://lore.kernel.org/linux-doc/cover.1622454385.git.charante@codeaurora.org/
>
>>
>> > In these machines we only care about order of 3 or 4.
>> > This patch export the oder to proc and let it configurable by user,
>> > and the default value is still COMPACTION_HPAGE_ORDER.
>> >
>> > Signed-off-by: chukaiping <chukaiping@...du.com>
>> > Reported-by: kernel test robot <lkp@...el.com>
>> > ---
>> >
>> > Changes in v4:
>> > - change the sysctl file name to proactive_compation_order
>> >
>> > Changes in v3:
>> > - change the min value of compaction_order to 1 because the
>> fragmentation
>> > index of order 0 is always 0
>> > - move the definition of max_buddy_zone into #ifdef
>> > CONFIG_COMPACTION
>> >
>> > Changes in v2:
>> > - fix the compile error in ia64 and powerpc, move the initialization
>> > of sysctl_compaction_order to kcompactd_init because
>> > COMPACTION_HPAGE_ORDER is a variable in these architectures
>> > - change the hard coded max order number from 10 to MAX_ORDER - 1
>> >
>> > include/linux/compaction.h | 1 +
>> > kernel/sysctl.c | 10 ++++++++++
>> > mm/compaction.c | 12 ++++++++----
>> > 3 files changed, 19 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/include/linux/compaction.h b/include/linux/compaction.h
>> > index ed4070e..a0226b1 100644
>> > --- a/include/linux/compaction.h
>> > +++ b/include/linux/compaction.h
>> > @@ -83,6 +83,7 @@ static inline unsigned long compact_gap(unsigned int
>> > order) #ifdef CONFIG_COMPACTION extern int sysctl_compact_memory;
>> > extern unsigned int sysctl_compaction_proactiveness;
>> > +extern unsigned int sysctl_proactive_compaction_order;
>> > extern int sysctl_compaction_handler(struct ctl_table *table, int write,
>> > void *buffer, size_t *length, loff_t *ppos); extern int
>> > sysctl_extfrag_threshold; diff --git a/kernel/sysctl.c
>> > b/kernel/sysctl.c index 62fbd09..ed9012e 100644
>> > --- a/kernel/sysctl.c
>> > +++ b/kernel/sysctl.c
>> > @@ -196,6 +196,7 @@ enum sysctl_writes_mode { #endif /*
>> > CONFIG_SCHED_DEBUG */
>> >
>> > #ifdef CONFIG_COMPACTION
>> > +static int max_buddy_zone = MAX_ORDER - 1;
>> > static int min_extfrag_threshold;
>> > static int max_extfrag_threshold = 1000; #endif @@ -2871,6 +2872,15
>> > @@ int proc_do_static_key(struct ctl_table *table, int write,
>> > .extra2 = &one_hundred,
>> > },
>> > {
>> > + .procname = "proactive_compation_order",
>> > + .data = &sysctl_proactive_compaction_order,
>> > + .maxlen = sizeof(sysctl_proactive_compaction_order),
>> > + .mode = 0644,
>> > + .proc_handler = proc_dointvec_minmax,
>> > + .extra1 = SYSCTL_ONE,
>> > + .extra2 = &max_buddy_zone,
>> > + },
>> > + {
>> > .procname = "extfrag_threshold",
>> > .data = &sysctl_extfrag_threshold,
>> > .maxlen = sizeof(int),
>> > diff --git a/mm/compaction.c b/mm/compaction.c index e04f447..171436e
>> > 100644
>> > --- a/mm/compaction.c
>> > +++ b/mm/compaction.c
>> > @@ -1925,17 +1925,18 @@ static bool kswapd_is_running(pg_data_t
>> > *pgdat)
>> >
>> > /*
>> > * A zone's fragmentation score is the external fragmentation wrt to
>> > the
>> > - * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100].
>> > + * sysctl_proactive_compaction_order. It returns a value in the range
>> > + * [0, 100].
>> > */
>> > static unsigned int fragmentation_score_zone(struct zone *zone) {
>> > - return extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
>> > + return extfrag_for_order(zone, sysctl_proactive_compaction_order);
>> > }
>> >
>> > /*
>> > * A weighted zone's fragmentation score is the external
>> > fragmentation
>> > - * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It
>> > - * returns a value in the range [0, 100].
>> > + * wrt to the sysctl_proactive_compaction_order scaled by the zone's size.
>> > + * It returns a value in the range [0, 100].
>> > *
>> > * The scaling factor ensures that proactive compaction focuses on larger
>> > * zones like ZONE_NORMAL, rather than smaller, specialized zones
>> > like @@ -2666,6 +2667,7 @@ static void compact_nodes(void)
>> > * background. It takes values in the range [0, 100].
>> > */
>> > unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
>> > +unsigned int __read_mostly sysctl_proactive_compaction_order;
>> >
>> > /*
>> > * This is the entry point for compacting all nodes via @@ -2958,6
>> > +2960,8 @@ static int __init kcompactd_init(void)
>> > int nid;
>> > int ret;
>> >
>> > + sysctl_proactive_compaction_order = COMPACTION_HPAGE_ORDER;
>> > +
>> > ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
>> > "mm/compaction:online",
>> > kcompactd_cpu_online, NULL);
>> >
>
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