RE: [PATCH v2] mm/compaction:let proactive compaction order configurable

[Nitin Gupta]

> -----Original Message-----
> From: chukaiping <chukaiping@xxxxxxxxx>
> Sent: Wednesday, April 21, 2021 12:22 AM
> To: mcgrof@xxxxxxxxxx; keescook@xxxxxxxxxxxx; yzaikin@xxxxxxxxxx;
> akpm@xxxxxxxxxxxxxxxxxxxx; vbabka@xxxxxxx; Nitin Gupta
> <nigupta@xxxxxxxxxx>; bhe@xxxxxxxxxx; khalid.aziz@xxxxxxxxxx;
> iamjoonsoo.kim@xxxxxxx; mateusznosek0@xxxxxxxxx; sh_def@xxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx; linux-
> mm@xxxxxxxxx
> Subject: [PATCH v2] mm/compaction:let proactive compaction order
> configurable
> 
> 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.
>

I agree with the idea of making the target order configurable as you may not
always care about the hugepage order in particular.
 
> Signed-off-by: chukaiping <chukaiping@xxxxxxxxx>
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> ---
> 
> Changes in v2:
>     - fix the compile error in ia64 and powerpc
>     - change the hard coded max order number from 10 to MAX_ORDER - 1
> 
>  include/linux/compaction.h |    1 +
>  kernel/sysctl.c            |   11 +++++++++++
>  mm/compaction.c            |   14 +++++++++++---
>  3 files changed, 23 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h index
> ed4070e..151ccd1 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_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..a607d4d 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -195,6 +195,8 @@ enum sysctl_writes_mode {  #endif /* CONFIG_SMP
> */  #endif /* CONFIG_SCHED_DEBUG */
> 
> +static int max_buddy_zone = MAX_ORDER - 1;
> +
>  #ifdef CONFIG_COMPACTION
>  static int min_extfrag_threshold;
>  static int max_extfrag_threshold = 1000; @@ -2871,6 +2873,15 @@ int
> proc_do_static_key(struct ctl_table *table, int write,
>                 .extra2         = &one_hundred,
>         },
>         {
> +               .procname       = "compaction_order",
> +               .data           = &sysctl_compaction_order,
> +               .maxlen         = sizeof(sysctl_compaction_order),
> +               .mode           = 0644,
> +               .proc_handler   = proc_dointvec_minmax,
> +               .extra1         = SYSCTL_ZERO,

This should be SYSCTL_ONE. Fragmentation wrt order 0 is always going to be 0.

Thanks,
Nitin