答复: [PATCH v4] mm/compaction: let proactive compaction order configurable

[Chu,Kaiping]

> -----邮件原件-----
> 发件人: Vlastimil Babka <vbabka@xxxxxxx>
> 发送时间: 2021年5月29日 1:42
> 收件人: Chu,Kaiping <chukaiping@xxxxxxxxx>; mcgrof@xxxxxxxxxx;
> keescook@xxxxxxxxxxxx; yzaikin@xxxxxxxxxx; akpm@xxxxxxxxxxxxxxxxxxxx;
> nigupta@xxxxxxxxxx; bhe@xxxxxxxxxx; khalid.aziz@xxxxxxxxxx;
> iamjoonsoo.kim@xxxxxxx; mateusznosek0@xxxxxxxxx; sh_def@xxxxxxx
> 抄送: linux-kernel@xxxxxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx;
> linux-mm@xxxxxxxxx
> 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.

> 
> > 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@xxxxxxxxx>
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > ---
> >
> > 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);
> >