linux-kernel - [PATCH 0/5] mm: rework sys_move_pages() to avoid vmalloc and reduce the overhead

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Date:	Mon, 13 Oct 2008 22:19:19 +0200
From:	Brice Goglin <Brice.Goglin@...ia.fr>
To:	Christoph Lameter <cl@...ux-foundation.org>
CC:	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	Andrew Morton <akpm@...l.org>,
	Nathalie Furmento <nathalie.furmento@...ri.fr>
Subject: [PATCH 0/5] mm: rework sys_move_pages() to avoid vmalloc and reduce
 the overhead

Hello,

Here's the first patchset reworking sys_move_pages() as discussed earlier.
It removes the possibly large vmalloc by using multiple chunks when migrating
large buffers. It also dramatically increases the throughput for large buffers
since the lookup in new_page_node() is now limited to a single chunk, causing
the quadratic complexity to have a much slower impact. There is no need to use
any radix-tree-like structure to improve this lookup.

sys_move_pages() duration on a 4-quadcore-opteron 2347HE (1.9Gz), migrating
between nodes #2 and #3:
	length		move_pages (us)		move_pages+patch (us)
	4kB		126			98
	40kB		198			168
	400kB		963			937
	4MB		12503			11930
	40MB		246867			11848

Patches #1 and #4 are the important ones:
1) stop returning -ENOENT from sys_move_pages() if nothing got migrated
2) don't vmalloc a huge page_to_node array for do_pages_stat()
3) extract do_pages_move() out of sys_move_pages()
4) rework do_pages_move() to work on page_sized chunks
5) move_pages: no need to set pp->page to ZERO_PAGE(0) by default

thanks,
Brice


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