Re: [RFC PATCH v3 6/7] mm/damon/paddr: introduce DAMOS_MIGRATE_HOT action for promotion

SeongJae Park
2024-04-05T19:26:53Z

On Fri, 5 Apr 2024 15:08:55 +0900 Honggyu Kim <honggyu.kim@sk.com> wrote:

> From: Hyeongtak Ji <hyeongtak.ji@sk.com>
>
> This patch introduces DAMOS_MIGRATE_HOT action, which is similar to
> DAMOS_MIGRATE_COLD, but it is targeted to migrate hot pages.

My understanding of our last discussion was that 'HOT/COLD' here is only for
prioritization score function. If I'm not wrong, this is not for targeting,
but just prioritize migrating hot pages first under the quota.

>
> It migrates pages inside the given region to the 'target_nid' NUMA node
> in the sysfs.
>
> Here is one of the example usage of this 'migrate_hot' action.
>
> $ cd /sys/kernel/mm/damon/admin/kdamonds/<N>
> $ cat contexts/<N>/schemes/<N>/action
> migrate_hot
> $ echo 0 > contexts/<N>/schemes/<N>/target_nid
> $ echo commit > state
> $ numactl -p 2 ./hot_cold 500M 600M &
> $ numastat -c -p hot_cold
>
> Per-node process memory usage (in MBs)
> PID Node 0 Node 1 Node 2 Total
> -------------- ------ ------ ------ -----
> 701 (hot_cold) 501 0 601 1101
>
> Signed-off-by: Hyeongtak Ji <hyeongtak.ji@sk.com>
> Signed-off-by: Honggyu Kim <honggyu.kim@sk.com>
> ---
> include/linux/damon.h | 2 ++
> mm/damon/paddr.c | 12 ++++++++++--
> mm/damon/sysfs-schemes.c | 4 +++-
> 3 files changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/damon.h b/include/linux/damon.h
> index df8671e69a70..934c95a7c042 100644
> --- a/include/linux/damon.h
> +++ b/include/linux/damon.h
> @@ -105,6 +105,7 @@ struct damon_target {
> * @DAMOS_NOHUGEPAGE: Call ``madvise()`` for the region with MADV_NOHUGEPAGE.
> * @DAMOS_LRU_PRIO: Prioritize the region on its LRU lists.
> * @DAMOS_LRU_DEPRIO: Deprioritize the region on its LRU lists.
> + * @DAMOS_MIGRATE_HOT: Migrate for the given hot region.

As commented on the previous patch, this could be bit re-phrased.
Also, let's use tabs consistently.

> * @DAMOS_MIGRATE_COLD: Migrate for the given cold region.
> * @DAMOS_STAT: Do nothing but count the stat.
> * @NR_DAMOS_ACTIONS: Total number of DAMOS actions
> @@ -123,6 +124,7 @@ enum damos_action {
> DAMOS_NOHUGEPAGE,
> DAMOS_LRU_PRIO,
> DAMOS_LRU_DEPRIO,
> + DAMOS_MIGRATE_HOT,
> DAMOS_MIGRATE_COLD,
> DAMOS_STAT, /* Do nothing but only record the stat */
> NR_DAMOS_ACTIONS,
> diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
> index fe217a26f788..fd9d35b5cc83 100644
> --- a/mm/damon/paddr.c
> +++ b/mm/damon/paddr.c
> @@ -229,6 +229,7 @@ static bool damos_pa_filter_out(struct damos *scheme, struct folio *folio)
>
> enum migration_mode {
> MIG_PAGEOUT,
> + MIG_MIGRATE_HOT,
> MIG_MIGRATE_COLD,
> };

It looks like we don't need MIG_MIGRATE_HOT and MIG_MIGRATE_COLD in real, but
just one, say, MIG_MIGRATE, since the code can know if it should use what
prioritization score function with DAMOS action?

Also, as I commented on the previous one, I'd prefer having DAMOS_ prefix.

>
> @@ -375,8 +376,10 @@ static unsigned long damon_pa_migrate(struct damon_region *r, struct damos *s,
> if (damos_pa_filter_out(s, folio))
> goto put_folio;
>
> - folio_clear_referenced(folio);
> - folio_test_clear_young(folio);
> + if (mm != MIG_MIGRATE_HOT) {
> + folio_clear_referenced(folio);
> + folio_test_clear_young(folio);
> + }

We agreed to this check via 'young' page type DAMOS filter, and let this
doesn't care about it, right? If I'm not wrong, I think this should be
removed?

> if (!folio_isolate_lru(folio))
> goto put_folio;
> /*
> @@ -394,6 +397,7 @@ static unsigned long damon_pa_migrate(struct damon_region *r, struct damos *s,
> case MIG_PAGEOUT:
> applied = reclaim_pages(&folio_list);
> break;
> + case MIG_MIGRATE_HOT:
> case MIG_MIGRATE_COLD:
> applied = damon_pa_migrate_pages(&folio_list, mm,
> s->target_nid);
> @@ -454,6 +458,8 @@ static unsigned long damon_pa_apply_scheme(struct damon_ctx *ctx,
> return damon_pa_mark_accessed(r, scheme);
> case DAMOS_LRU_DEPRIO:
> return damon_pa_deactivate_pages(r, scheme);
> + case DAMOS_MIGRATE_HOT:
> + return damon_pa_migrate(r, scheme, MIG_MIGRATE_HOT);
> case DAMOS_MIGRATE_COLD:
> return damon_pa_migrate(r, scheme, MIG_MIGRATE_COLD);
> case DAMOS_STAT:
> @@ -476,6 +482,8 @@ static int damon_pa_scheme_score(struct damon_ctx *context,
> return damon_hot_score(context, r, scheme);
> case DAMOS_LRU_DEPRIO:
> return damon_cold_score(context, r, scheme);
> + case DAMOS_MIGRATE_HOT:
> + return damon_hot_score(context, r, scheme);
> case DAMOS_MIGRATE_COLD:
> return damon_cold_score(context, r, scheme);
> default:
> diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
> index 18b7d054c748..1d2f62aa79ca 100644
> --- a/mm/damon/sysfs-schemes.c
> +++ b/mm/damon/sysfs-schemes.c
> @@ -1406,6 +1406,7 @@ static const char * const damon_sysfs_damos_action_strs[] = {
> "nohugepage",
> "lru_prio",
> "lru_deprio",
> + "migrate_hot",
> "migrate_cold",
> "stat",
> };
> @@ -1660,7 +1661,8 @@ static ssize_t target_nid_store(struct kobject *kobj,
> struct damon_sysfs_scheme, kobj);
> int err = 0;
>
> - if (scheme->action != DAMOS_MIGRATE_COLD)
> + if (scheme->action != DAMOS_MIGRATE_HOT &&
> + scheme->action != DAMOS_MIGRATE_COLD)
> return -EINVAL;
>
> /* TODO: error handling for target_nid range. */
> --
> 2.34.1
>
>

Thanks,
SJ