Re: [RFC 4/4] mm, page_alloc: disallow migratetype fallback in fastpath

From: Vlastimil Babka
Date: Wed Oct 12 2016 - 11:15:08 EST

On 09/29/2016 11:05 PM, Vlastimil Babka wrote:
> The previous patch has adjusted async compaction so that it helps against
> longterm fragmentation when compacting for a non-MOVABLE high-order allocation.
> The goal of this patch is to force such allocations go through compaction
> once before being allowed to fallback to a pageblock of different migratetype
> (e.g. MOVABLE). In contexts where compaction is not allowed (and for order-0
> allocations), this delayed fallback possibility can still help by trying a
> different zone where fallback might not be needed and potentially waking up
> kswapd earlier.
> Not-yet-signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>

I forgot that compaction itself also needs to be told to not allow fallback,
otherwise it finishes with COMPACT_SUCCESS without actually doing anything...