[PATCH 07/34] mm, vmscan: make kswapd reclaim in terms of nodes

[Srikar Dronamraju]

> mm, vmscan: Only allocate and reclaim from zones with pages managed by the buddy allocator
> 
> Firmware Assisted Dump (FA_DUMP) on ppc64 reserves substantial amounts
> of memory when booting a secondary kernel. Srikar Dronamraju reported that
> multiple nodes may have no memory managed by the buddy allocator but still
> return true for populated_zone().
> 
> Commit 1d82de618ddd ("mm, vmscan: make kswapd reclaim in terms of nodes")
> was reported to cause kswapd to spin at 100% CPU usage when fadump was
> enabled. The old code happened to deal with the situation of a populated
> node with zero free pages by co-incidence but the current code tries to
> reclaim populated zones without realising that is impossible.
> 
> We cannot just convert populated_zone() as many existing users really
> need to check for present_pages. This patch introduces a managed_zone()
> helper and uses it in the few cases where it is critical that the check
> is made for managed pages -- zonelist constuction and page reclaim.

one nit
s/constuction/construction/

> 

Verified that it works fine.

-- 
Thanks and Regards
Srikar Dronamraju