Re: [RFC][PATCH 03/10] zsmalloc: introduce zs_can_compact() function

Sergey Senozhatsky
2015-06-04T03:14:58Z

On (06/04/15 11:55), Minchan Kim wrote:
> > [ 3303.108960] class-3072 objs:24652 inuse:24628 objs-per-page:4 pages-tofree:6
>
> maxobjs-per-zspage?
>

yeah, I shortened it to be more of less "80 chars" friendly.

[..]

> > + * calculate how many unused allocated objects we
>
> c should be captital.
>
> I hope you will fix all of english grammer in next spin
> because someone(like me) who is not a native will learn the
> wrong english. :)

sure, will fix. yeah, I'm a native broken english speaker :-)

> > + * have and see if we can free any zspages. otherwise,
> > + * compaction can just move objects back and forth w/o
> > + * any memory gain.
> > + */
> > + unsigned long ret = zs_stat_get(class, OBJ_ALLOCATED) -
> > + zs_stat_get(class, OBJ_USED);
> > +
>
> I prefer obj_wasted to "ret".

ok.

I'm still thinking how good it should be.

for automatic compaction we don't want to uselessly move objects between
pages and I tend to think that it's better to compact less, than to waste
more cpu cycless.

on the other hand, this policy will miss cases like:

-- free objects in class: 5 (free-objs class capacity)
-- page1: inuse 2
-- page2: inuse 2
-- page3: inuse 3
-- page4: inuse 2

so total "insuse" is greater than free-objs class capacity. but, it's
surely possible to compact this class. partial inuse summ <= free-objs class
capacity (a partial summ is a ->inuse summ of any two of class pages:
page1 + page2, page2 + page3, etc.).

otoh, these partial sums will badly affect performance. may be for automatic
compaction (the one that happens w/o user interaction) we can do zs_can_compact()
and for manual compaction (the one that has been triggered by a user) we can
old "full-scan".

anyway, zs_can_compact() looks like something that we can optimize
independently later.

-ss

> > + ret /= get_maxobj_per_zspage(class->size,
> > + class->pages_per_zspage);
> > + return ret > 0;
> > +}
> > +
> > static unsigned long __zs_compact(struct zs_pool *pool,
> > struct size_class *class)
> > {
> > @@ -1686,6 +1708,9 @@ static unsigned long __zs_compact(struct zs_pool *pool,
> >
> > BUG_ON(!is_first_page(src_page));
> >
> > + if (!zs_can_compact(class))
> > + break;
> > +
> > cc.index = 0;
> > cc.s_page = src_page;
> >
> > --
> > 2.4.2.337.gfae46aa
> >
>
> --
> Kind regards,
> Minchan Kim
>