On 08/16/2016 08:12 AM, Joonsoo Kim wrote:

On Wed, Aug 10, 2016 at 11:12:19AM +0200, Vlastimil Babka wrote:

quoted

Joonsoo has reminded me that in a later patch changing watermark checks
throughout compaction I forgot to update checks in try_to_compact_pages() and
compactd_do_work(). Closer inspection however shows that they are redundant now
that compact_zone() reliably reports success with COMPACT_SUCCESS, as they just
repeat (a subset) of checks that have just passed. So instead of checking
watermarks again, just test the return value.

In fact, it's not redundant. Even if try_to_compact_pages() returns
!COMPACT_SUCCESS, watermark check could return true.

Right, I meant they are redundant in the SUCCESS case.

__compact_finished() calls find_suitable_fallback() and it's slightly
different with watermark check. Anyway, I don't think it is a big
problem.

I agree. It might be even better for long-term fragmentation that we 
e.g. try another zone instead of taking page from the "unsuitable 
fallback". If that's not successful, and the allocation is important 
enough there will later eventually be another watermark check permitting 
the unsuitable fallback.

Thanks.

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