Re: [PATCH] mm/vmscan: simplify the nr assignment logic for pages to scan

[Chao Xu]

在 2022/11/10 9:19, Andrew Morton 写道:
> On Wed,  9 Nov 2022 15:04:16 +0800 Chao Xu <amos.xuchao@xxxxxxxxx> wrote:
>
> > By default the assignment logic of anonymouns or file inactive
> > pages and active pages to scan using the same duplicated code
> > snippet. To simplify the logic, merge the same part.
> >
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -5932,14 +5932,11 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
> >   		 * scan target and the percentage scanning already complete
> >   		 */
> >   		lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
> > -		nr_scanned = targets[lru] - nr[lru];
> > -		nr[lru] = targets[lru] * (100 - percentage) / 100;
> > -		nr[lru] -= min(nr[lru], nr_scanned);
> > -
> > -		lru += LRU_ACTIVE;
> > -		nr_scanned = targets[lru] - nr[lru];
> > -		nr[lru] = targets[lru] * (100 - percentage) / 100;
> > -		nr[lru] -= min(nr[lru], nr_scanned);
> > +		for ( ; lru <= lru + LRU_ACTIVE; lru++) {
> The "lru++" implicitly assumes that LRU_ACTIVE=1.  That happens to be
> the case, but a more accurate translation of the existing code would
> use "lru += LRU_ACTIVE" here, yes?
By default the value of LRU_ACTIVE is 1，but if someone change it one day, I
use "lru++" maybe facing some exceptions, which is not robust. So I 
agree with
that "lru += LRU_ACTIVE" is appropriate instead of "lru++". I will send 
a new patch.
> > +			nr_scanned = targets[lru] - nr[lru];
> > +			nr[lru] = targets[lru] * (100 - percentage) / 100;
> > +			nr[lru] -= min(nr[lru], nr_scanned);
> > +		}
> >   
> >   		scan_adjusted = true;
> >   	}