Re: why inode creation with GFP_HIGHUSER?

[Christoph Lameter <clameter@sgi.com>]

On Thu, 14 Sep 2006, girish wrote:

> > I am not sure what you intend to do. The kernel already avoids mapping
> > highmem pages into the kernel as much as possible.
> 
> that's the whole confusion. kernel is supposed to *avoid* allocating
> from ZONE_HIGHMEM if there is some memory left in ZONE_DMA and/or

The kernel favors ZONE_HIGHMEM allocations for certain type of 
allocations. Like those marked GF_HIGHUSER. It avoid establishing
mappings of its own. The mappings via the page tables are easier on
the machine and so the application will be fine with HIGHMEM pages.

> ZONE_NORMAL. but as i mentioned the zonelist selection that happens
> based  on GFP_* mask (in this case GFP_HIGHUSER), makes __alloc_pages
> to allocate from a list which has both HIGHMEM and DMA/NORMAL zones
> listed in it. the zonelist looping/fallback is as implemented in
> get_page_from_freelist (). to this function, the zonelist that is
> passed contains both and in the order - HIGHMEM and DMA/NORMAL zones.
> shouldn't it be NORMAl/DMA first and then HIGHMEM in the zonelist?

The fallback sequence is HIGHMEM / NORMAL / DMA for a GFP_HIGHUSER 
allocation.


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