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

["Chu,Kaiping" <chukaiping@baidu.com>]

> -----邮件原件-----
> 发件人: David Hildenbrand <david@redhat.com>
> 发送时间: 2021年6月9日 18:45
> 收件人: Chu,Kaiping <chukaiping@baidu.com>; mcgrof@kernel.org;
> keescook@chromium.org; yzaikin@google.com; akpm@linux-foundation.org;
> vbabka@suse.cz; nigupta@nvidia.com; bhe@redhat.com;
> khalid.aziz@oracle.com; iamjoonsoo.kim@lge.com;
> mateusznosek0@gmail.com; sh_def@163.com
> 抄送: linux-kernel@vger.kernel.org; linux-fsdevel@vger.kernel.org;
> linux-mm@kvack.org
> 主题: Re: [PATCH v4] mm/compaction: let proactive compaction order
> configurable
> 
> On 28.04.21 04:28, 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. 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@baidu.com>
> > Reported-by: kernel test robot <lkp@intel.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);
> >
> 
> Hm, do we actually want to put an upper limit to the order a user can supply?
No，we should allow user to configure the order from 1 to MAX_ORDER - 1.
> 
> --
> Thanks,
> 
> David / dhildenb