linux-kernel - Re: [RFC][PATCHv3 4/7] zsmalloc: introduce zs_can

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Date:	Mon, 29 Jun 2015 17:58:53 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [RFC][PATCHv3 4/7] zsmalloc: introduce zs_can_compact() function

On (06/29/15 15:45), Minchan Kim wrote:
[..]
> > +/*
> > + * Make sure that we actually can compact this class,
> > + * IOW if migration will release at least one szpage.
> 
>                                                  zspage,

ok.

> > + *
> > + * Should be called under class->lock
> 
> Please comment about return.

ok.

> > + */
> > +static unsigned long zs_can_compact(struct size_class *class)
> > +{
> > +	/*
> > +	 * Calculate how many unused allocated objects we
> > +	 * 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 obj_wasted = zs_stat_get(class, OBJ_ALLOCATED) -
> > +		zs_stat_get(class, OBJ_USED);
> > +
> 
> I want to check one more thing.
> 
> We could have lots of ZS_ALMOST_FULL but no ZS_ALMOST_EMPTY.
> In this implementation, compaction cannot have a source so
> it would better to bail out.
> IOW,
> 
>       if (!zs_stat_get(class, CLASS_ALMOST_EMPTY))
>               return 0;

ok.

	-ss
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