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

Vlastimil Babka
2015-09-17T06:21:57Z

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?