Re: [PATCH 3/4] alloc_contig_pages() allocate big chunk memory using migration

[Minchan Kim <minchan.kim@gmail.com>]

On Fri, Nov 19, 2010 at 5:15 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>
> Add an function to allocate contiguous memory larger than MAX_ORDER.
> The main difference between usual page allocator is that this uses
> memory offline technique (Isolate pages and migrate remaining pages.).
>
> I think this is not 100% solution because we can't avoid fragmentation,
> but we have kernelcore= boot option and can create MOVABLE zone. That
> helps us to allow allocate a contiguous range on demand.

And later we can use compaction and reclaim, too.
So I think this approach is the way we have to go.

>
> The new function is
>
>  alloc_contig_pages(base, end, nr_pages, alignment)
>
> This function will allocate contiguous pages of nr_pages from the range
> [base, end). If [base, end) is bigger than nr_pages, some pfn which
> meats alignment will be allocated. If alignment is smaller than MAX_ORDER,

type meet

> it will be raised to be MAX_ORDER.
>
> __alloc_contig_pages() has much more arguments.
>
>
> Some drivers allocates contig pages by bootmem or hiding some memory
> from the kernel at boot. But if contig pages are necessary only in some
> situation, kernelcore= boot option and using page migration is a choice