On 6/1/21 3:15 AM, Chu,Kaiping wrote: > > >> -----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. 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@xxxxxxxxxxxxxx/ > >> >> > 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); >> > >
