Re: [PATCH 2/4] tracing, mm: Add trace events for anti-fragmentation falling back to other migratetypes

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

> Fragmentation avoidance depends on being able to use free pages from
> lists of the appropriate migrate type. In the event this is not
> possible, __rmqueue_fallback() selects a different list and in some
> circumstances change the migratetype of the pageblock. Simplistically,
> the more times this event occurs, the more likely that fragmentation
> will be a problem later for hugepage allocation at least but there are
> other considerations such as the order of page being split to satisfy
> the allocation.
> 
> This patch adds a trace event for __rmqueue_fallback() that reports what
> page is being used for the fallback, the orders of relevant pages, the
> desired migratetype and the migratetype of the lists being used, whether
> the pageblock changed type and whether this event is important with
> respect to fragmentation avoidance or not. This information can be used
> to help analyse fragmentation avoidance and help decide whether
> min_free_kbytes should be increased or not.
> 
> Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> Acked-by: Rik van Riel <riel@redhat.com>

Looks good to me.
but I don't put my reviewed-by because I am not so familiar this area.



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