Re: [PATCH V2] mm/damon: simplify scheme create in lru_sort.c

[haoxin]

在 2022/9/14 下午10:22, SeongJae Park 写道:
> Hi Xin,
>
> On Wed, 14 Sep 2022 19:38:59 +0800 Xin Hao <xhao@xxxxxxxxxxxxxxxxx> wrote:
>
> > In damon_lru_sort_new_hot_scheme() and damon_lru_sort_new_cold_scheme(),
> > they have so much in common, so we can combine them into a single
> > function, and we just need to distinguish their differences.
> Thank you again for patiently waiting for my changes and reworking on this!
>
> > Signed-off-by: Xin Hao <xhao@xxxxxxxxxxxxxxxxx>
> > ---
> >   mm/damon/lru_sort.c | 57 ++++++++++++++++++++++-----------------------
> >   1 file changed, 28 insertions(+), 29 deletions(-)
> >
> > diff --git a/mm/damon/lru_sort.c b/mm/damon/lru_sort.c
> > index 07a0908963fd..2eac907e866d 100644
> > --- a/mm/damon/lru_sort.c
> > +++ b/mm/damon/lru_sort.c
> > @@ -135,17 +135,40 @@ DEFINE_DAMON_MODULES_DAMOS_STATS_PARAMS(damon_lru_sort_cold_stat,
> >   static struct damon_ctx *ctx;
> >   static struct damon_target *target;
> >   
> > -static struct damos *damon_lru_sort_new_scheme(
> > -		struct damos_access_pattern *pattern, enum damos_action action)
> > +static struct damos *damon_lru_sort_new_scheme(unsigned int thres,
> > +					       enum damos_action action)
> >   {
> > +	struct damos_access_pattern pattern = {
> > +		/* Find regions having PAGE_SIZE or larger size */
> > +		.min_sz_region = PAGE_SIZE,
> > +		.max_sz_region = ULONG_MAX,
> > +		/* and accessed for more than the threshold */
> This comment would be better to be written again?
>
> > +		.min_nr_accesses = 0,
> > +		.max_nr_accesses = 0,
> If we're gonna set above two fields anyway later, we could simply remove above
> three lines.
>
> > +		/* no matter its age */
> > +		.min_age_region = 0,
> > +		.max_age_region = UINT_MAX,
> > +	};
> >   	struct damos_quota quota = damon_lru_sort_quota;
> >   
> >   	/* Use half of total quota for hot/cold pages sorting */
> >   	quota.ms = quota.ms / 2;
> >   
> > +	switch (action) {
> > +	case DAMOS_LRU_PRIO:
> > +		pattern.min_nr_accesses = thres;
> > +		pattern.max_nr_accesses = UINT_MAX;
> > +		break;
> > +	case DAMOS_LRU_DEPRIO:
> > +		pattern.min_age_region = thres;
> > +		break;
> > +	default:
> > +		return NULL;
> > +	}
> > +
> This switch-case makes me wondering if the 'default' case really possible case.
> I think it would be clearer to set these from caller.
>
> IMHO, it might be clearer and shorter to define a static global 'struct
> damos_access_pattern' stub variable, and make the
> damon_lru_sort_new_{hot,cold}_scheme() copies it to their local variable,
> update the relevant fields, and pass that to 'damon_new_scheme()'.  What do you
> think?
>
> >   	return damon_new_scheme(
> >   			/* find the pattern, and */
> > -			pattern,
> > +			&pattern,
> >   			/* (de)prioritize on LRU-lists */
> >   			action,
> >   			/* under the quota. */
> > @@ -157,37 +180,13 @@ static struct damos *damon_lru_sort_new_scheme(
> >   /* Create a DAMON-based operation scheme for hot memory regions */
> >   static struct damos *damon_lru_sort_new_hot_scheme(unsigned int hot_thres)
> >   {
> > -	struct damos_access_pattern pattern = {
> > -		/* Find regions having PAGE_SIZE or larger size */
> > -		.min_sz_region = PAGE_SIZE,
> > -		.max_sz_region = ULONG_MAX,
> > -		/* and accessed for more than the threshold */
> > -		.min_nr_accesses = hot_thres,
> > -		.max_nr_accesses = UINT_MAX,
> > -		/* no matter its age */
> > -		.min_age_region = 0,
> > -		.max_age_region = UINT_MAX,
> > -	};
> > -
> > -	return damon_lru_sort_new_scheme(&pattern, DAMOS_LRU_PRIO);
> > +	return damon_lru_sort_new_scheme(hot_thres, DAMOS_LRU_PRIO);
> If we follow what I suggested above, we could make this like below:
>
> 	struct damos_access_pattern pattern = damon_lru_sort_stub_access_pattern;
>
> 	pattern.min_nr_accesses = hot_thres;
> 	return damon_lru_sort_new_scheme(&pattern, DAMOS_LRU_PRIO);
Agree totally,  i will fix it in the next patch.
> >   }
> >   
> >   /* Create a DAMON-based operation scheme for cold memory regions */
> >   static struct damos *damon_lru_sort_new_cold_scheme(unsigned int cold_thres)
> >   {
> > -	struct damos_access_pattern pattern = {
> > -		/* Find regions having PAGE_SIZE or larger size */
> > -		.min_sz_region = PAGE_SIZE,
> > -		.max_sz_region = ULONG_MAX,
> > -		/* and not accessed at all */
> > -		.min_nr_accesses = 0,
> > -		.max_nr_accesses = 0,
> > -		/* for min_age or more micro-seconds */
> > -		.min_age_region = cold_thres,
> > -		.max_age_region = UINT_MAX,
> > -	};
> > -
> > -	return damon_lru_sort_new_scheme(&pattern, DAMOS_LRU_DEPRIO);
> > +	return damon_lru_sort_new_scheme(cold_thres, DAMOS_LRU_DEPRIO);
> And similarly here.
>
> >   }
> >   
> >   static int damon_lru_sort_apply_parameters(void)
> > --
> > 2.31.0
>
> Thanks,
> SJ