linux-kernel - Re: [PATCH 0/3] allow zram to use zbud as underlying allocator

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Date:	Thu, 17 Sep 2015 08:21:50 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Dan Streetman <ddstreet@...e.org>
Cc:	Vitaly Wool <vitalywool@...il.com>,
	Minchan Kim <minchan@...nel.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 0/3] allow zram to use zbud as underlying allocator

On 09/15/2015 06:22 AM, Sergey Senozhatsky wrote:
> On (09/15/15 00:08), Dan Streetman wrote:
> [..]
>
> correct. a bit of internals: we don't scan all the zspages every
> time. each class has stats for allocated used objects, allocated
> used objects, etc. so we 'compact' only classes that can be
> compacted:
>
>   static unsigned long zs_can_compact(struct size_class *class)
>   {
>           unsigned long obj_wasted;
>
>           obj_wasted = zs_stat_get(class, OBJ_ALLOCATED) -
>                   zs_stat_get(class, OBJ_USED);
>
>           obj_wasted /= get_maxobj_per_zspage(class->size,
>                           class->pages_per_zspage);
>
>           return obj_wasted * class->pages_per_zspage;
>   }
>
> if we can free any zspages (which is at least one page), then we
> attempt to do so.
>
> is compaction the root cause of the symptoms Vitaly observe?

He mentioned the "compact_stalls" counter which in /proc/vmstat is for 
the traditional physical memory compaction, not the zsmalloc-specific 
one. Which would imply high-order allocations. Does zsmalloc try them 
first before falling back to the order-0 zspages linked together manually?

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