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From:   Nitin Gupta <nigupta@nvidia.com>
To:     chukaiping <chukaiping@baidu.com>,
        "mcgrof@kernel.org" <mcgrof@kernel.org>,
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        "linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: RE: [PATCH v2] mm/compaction:let proactive compaction order
 configurable
Thread-Topic: [PATCH v2] mm/compaction:let proactive compaction order
 configurable
Thread-Index: AQHXNn8EHJajSRkDM02ntF/mlIkikqrAufsg
Date:   Thu, 22 Apr 2021 16:27:00 +0000
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> -----Original Message-----
> From: chukaiping <chukaiping@baidu.com>
> Sent: Wednesday, April 21, 2021 12:22 AM
> To: mcgrof@kernel.org; keescook@chromium.org; yzaikin@google.com;
> akpm@linux-foundation.org; vbabka@suse.cz; Nitin Gupta
> <nigupta@nvidia.com>; bhe@redhat.com; khalid.aziz@oracle.com;
> iamjoonsoo.kim@lge.com; mateusznosek0@gmail.com; sh_def@163.com
> Cc: linux-kernel@vger.kernel.org; linux-fsdevel@vger.kernel.org; linux-
> mm@kvack.org
> Subject: [PATCH v2] mm/compaction:let proactive compaction order
> configurable
>=20
> 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 of=
ten
> below 9, and it's always below 9 even with hard compaction. This will lea=
d to
> proactive compaction be triggered very frequently. In these machines we o=
nly
> care about order of 3 or 4.
> This patch export the oder to proc and let it configurable by user, and t=
he
> default value is still COMPACTION_HPAGE_ORDER.
>

I agree with the idea of making the target order configurable as you may no=
t
always care about the hugepage order in particular.
=20
> Signed-off-by: chukaiping <chukaiping@baidu.com>
> Reported-by: kernel test robot <lkp@intel.com>
> ---
>=20
> Changes in v2:
>     - fix the compile error in ia64 and powerpc
>     - change the hard coded max order number from 10 to MAX_ORDER - 1
>=20
>  include/linux/compaction.h |    1 +
>  kernel/sysctl.c            |   11 +++++++++++
>  mm/compaction.c            |   14 +++++++++++---
>  3 files changed, 23 insertions(+), 3 deletions(-)
>=20
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h inde=
x
> 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);  ext=
ern 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 */
>=20
> +static int max_buddy_zone =3D MAX_ORDER - 1;
> +
>  #ifdef CONFIG_COMPACTION
>  static int min_extfrag_threshold;
>  static int max_extfrag_threshold =3D 1000; @@ -2871,6 +2873,15 @@ int
> proc_do_static_key(struct ctl_table *table, int write,
>                 .extra2         =3D &one_hundred,
>         },
>         {
> +               .procname       =3D "compaction_order",
> +               .data           =3D &sysctl_compaction_order,
> +               .maxlen         =3D sizeof(sysctl_compaction_order),
> +               .mode           =3D 0644,
> +               .proc_handler   =3D proc_dointvec_minmax,
> +               .extra1         =3D SYSCTL_ZERO,

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

Thanks,
Nitin