Re: [PATCH] mm: fix a regression with HIGHMEM introduced by changeset7f1290f2f2a4d

[David Rientjes]

On Thu, 15 Nov 2012, Jiang Liu wrote:

> I feel that zone->present_pages has been abused. I guess it means "physical pages 
> present in this zone" originally, but now sometimes zone->present_pages is used as
> "pages in this zone managed by the buddy system".

It's definition is all pages spanned by the zone that are not reserved and 
unavailable to the kernel to allocate from, and the implementation of 
bootmem requires that its memory be considered as "reserved" until freed.  
It's used throughout the kernel to determine the amount of memory that is 
allocatable in that zone from the page allocator since its reclaim 
heuristics and watermarks depend on this memory being allocatable.

> So I'm trying to add a new
> field "managed_pages" into zone, which accounts for pages managed by buddy system.
> That's why I thought the clean solution is a little complex:(
> 

You need to update the pgdat's node_present_pages to be consistent with 
all of its zones' present_pages.
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