linux-kernel - Re: [RFC PATCH v3 5/7] mm/damon/paddr: introduce DAMOS_MIGRATE

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Date: Fri,  5 Apr 2024 12:24:57 -0700
From: SeongJae Park <sj@...nel.org>
To: Hyeongtak Ji <hyeongtak.ji@...il.com>
Cc: SeongJae Park <sj@...nel.org>,
	Honggyu Kim <honggyu.kim@...com>,
	akpm@...ux-foundation.org,
	apopple@...dia.com,
	baolin.wang@...ux.alibaba.com,
	dave.jiang@...el.com,
	hyeongtak.ji@...com,
	kernel_team@...ynix.com,
	linmiaohe@...wei.com,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	mathieu.desnoyers@...icios.com,
	mhiramat@...nel.org,
	rakie.kim@...com,
	rostedt@...dmis.org,
	surenb@...gle.com,
	yangx.jy@...itsu.com,
	ying.huang@...el.com,
	ziy@...dia.com,
	42.hyeyoo@...il.com,
	art.jeongseob@...il.com
Subject: Re: [RFC PATCH v3 5/7] mm/damon/paddr: introduce DAMOS_MIGRATE_COLD action for demotion

On Fri,  5 Apr 2024 16:55:57 +0900 Hyeongtak Ji <hyeongtak.ji@...il.com> wrote:

> On Fri,  5 Apr 2024 15:08:54 +0900 Honggyu Kim <honggyu.kim@...com> wrote:
> 
> ...snip...
> 
> > +static unsigned long damon_pa_migrate_pages(struct list_head *folio_list,
> > +					    enum migration_mode mm,
> > +					    int target_nid)
> > +{
> > +	int nid;
> > +	unsigned int nr_migrated = 0;
> > +	LIST_HEAD(node_folio_list);
> > +	unsigned int noreclaim_flag;
> > +
> > +	if (list_empty(folio_list))
> > +		return nr_migrated;
> 
> How about checking if `target_nid` is `NUMA_NO_NODE` or not earlier,
> 
> > +
> > +	noreclaim_flag = memalloc_noreclaim_save();
> > +
> > +	nid = folio_nid(lru_to_folio(folio_list));
> > +	do {
> > +		struct folio *folio = lru_to_folio(folio_list);
> > +
> > +		if (nid == folio_nid(folio)) {
> > +			folio_clear_active(folio);
> > +			list_move(&folio->lru, &node_folio_list);
> > +			continue;
> > +		}
> > +
> > +		nr_migrated += damon_pa_migrate_folio_list(&node_folio_list,
> > +							   NODE_DATA(nid), mm,
> > +							   target_nid);
> > +		nid = folio_nid(lru_to_folio(folio_list));
> > +	} while (!list_empty(folio_list));
> > +
> > +	nr_migrated += damon_pa_migrate_folio_list(&node_folio_list,
> > +						   NODE_DATA(nid), mm,
> > +						   target_nid);
> > +
> > +	memalloc_noreclaim_restore(noreclaim_flag);
> > +
> > +	return nr_migrated;
> > +}
> > +
> 
> ...snip...
> 
> > +static unsigned int migrate_folio_list(struct list_head *migrate_folios,
> > +				       struct pglist_data *pgdat,
> > +				       int target_nid)
> > +{
> > +	unsigned int nr_succeeded;
> > +	nodemask_t allowed_mask = NODE_MASK_NONE;
> > +
> > +	struct migration_target_control mtc = {
> > +		/*
> > +		 * Allocate from 'node', or fail quickly and quietly.
> > +		 * When this happens, 'page' will likely just be discarded
> > +		 * instead of migrated.
> > +		 */
> > +		.gfp_mask = (GFP_HIGHUSER_MOVABLE & ~__GFP_RECLAIM) | __GFP_NOWARN |
> > +			__GFP_NOMEMALLOC | GFP_NOWAIT,
> > +		.nid = target_nid,
> > +		.nmask = &allowed_mask
> > +	};
> > +
> > +	if (pgdat->node_id == target_nid || target_nid == NUMA_NO_NODE)
> > +		return 0;
> 
> instead of here.

Agree.  As I replied on the previous reply, I think this check can be done from
the caller (or the caller of the caller) of this function.

> 
> > +
> > +	if (list_empty(migrate_folios))
> > +		return 0;

Same for this.

> > +
> > +	/* Migration ignores all cpuset and mempolicy settings */
> > +	migrate_pages(migrate_folios, alloc_migrate_folio, NULL,
> > +		      (unsigned long)&mtc, MIGRATE_ASYNC, MR_DAMON,
> > +		      &nr_succeeded);
> > +
> > +	return nr_succeeded;
> > +}
> > +
> 
> ...snip...
> 
> Kind regards,
> Hyeongtak
> 

Thanks,
SJ