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page allocator: use allocation flags as an index to the zone watermark

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ALLOC_WMARK_MIN, ALLOC_WMARK_LOW and ALLOC_WMARK_HIGH determin whether
pages_min, pages_low or pages_high is used as the zone watermark when
allocating the pages.  Two branches in the allocator hotpath determine
which watermark to use.

This patch uses the flags as an array index into a watermark array that is
indexed with WMARK_* defines accessed via helpers.  All call sites that
use zone->pages_* are updated to use the helpers for accessing the values
and the array offsets for setting.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Reviewed-by: Christoph Lameter <cl@linux-foundation.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mel Gorman
2009-06-16 15:32:12 -07:00
committed by Linus Torvalds
parent a3af9c389a
commit 418589663d
7 changed files with 83 additions and 64 deletions
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18
Documentation/vm/balance
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@@ -75,15 +75,15 @@ Page stealing from process memory and shm is done if stealing the page would
alleviate memory pressure on any zone in the page's node that has fallen below
its watermark.
pages_min/pages_low/pages_high/low_on_memory/zone_wake_kswapd: These are
per-zone fields, used to determine when a zone needs to be balanced. When
the number of pages falls below pages_min, the hysteric field low_on_memory
gets set. This stays set till the number of free pages becomes pages_high.
When low_on_memory is set, page allocation requests will try to free some
pages in the zone (providing GFP_WAIT is set in the request). Orthogonal
to this, is the decision to poke kswapd to free some zone pages. That
decision is not hysteresis based, and is done when the number of free
pages is below pages_low; in which case zone_wake_kswapd is also set.
watemark[WMARK_MIN/WMARK_LOW/WMARK_HIGH]/low_on_memory/zone_wake_kswapd: These
are per-zone fields, used to determine when a zone needs to be balanced. When
the number of pages falls below watermark[WMARK_MIN], the hysteric field
low_on_memory gets set. This stays set till the number of free pages becomes
watermark[WMARK_HIGH]. When low_on_memory is set, page allocation requests will
try to free some pages in the zone (providing GFP_WAIT is set in the request).
Orthogonal to this, is the decision to poke kswapd to free some zone pages.
That decision is not hysteresis based, and is done when the number of free
pages is below watermark[WMARK_LOW]; in which case zone_wake_kswapd is also set.
(Good) Ideas that I have heard: