Patch to convert global dirty_exceeded flag to per-node
node_dirty_exceeded.
dirty_exceeded ping pongs between nodes in order to force all cpus in
the system to increase the frequency of calls to balance_dirty_pages.
Currently dirty_exceeded is used by balance_dirty_pages_ratelimited to
force all CPUs in the system call balance_dirty_pages often, in order to
reduce the amount of dirty pages in the entire system (based on
dirty_thresh and one CPU exceeding thee ratelimits). As dirty_exceeded
is a global variable, it will ping-pong between nodes of a NUMA system
which is not good.
We think it is OK to reduce the affect of dirty_exceeded to node basis.
That will give us on one hand having multiple CPUs (of that node)
calling balance_dirty_pages often (based on same logic as before) and on
the other hand not causing ping-pong of dirty_exceeded with the other
nodes.
Following patch changes the global dirty_exceeded flag to a per-node
flag. Hence, balance_dirty_pages is called more often only on the node
which exceeded the dirty_threshold. The SMP case is left as was before.
Comments?
Signed-off-by: Alok N Kataria <[email protected]>
Signed-off-by: Ravikiran Thirumalai <[email protected]>
Signed-off-by: Shai Fultheim <[email protected]>
Index: linux-2.6.15-rc6/mm/page-writeback.c
===================================================================
--- linux-2.6.15-rc6.orig/mm/page-writeback.c 2005-12-21 18:29:38.000000000 -0800
+++ linux-2.6.15-rc6/mm/page-writeback.c 2005-12-21 23:43:33.000000000 -0800
@@ -46,7 +46,20 @@
static long ratelimit_pages = 32;
static long total_pages; /* The total number of pages in the machine. */
-static int dirty_exceeded; /* Dirty mem may be over limit */
+
+/*
+ * node_dirty_exceeded is used to indicate that dirty mem in the current node
+ * maybe over the limit and we need to increase the frequency of calls to
+ * balance_dirty_pages
+ */
+#ifdef CONFIG_NUMA
+static DEFINE_PER_CPU(int, _dirty_exceeded) = { 0 };
+#define node_dirty_exceeded \
+ per_cpu(_dirty_exceeded, node_to_first_cpu(numa_node_id()))
+#else
+static int node_dirty_exceeded;
+#endif
+
/*
* When balance_dirty_pages decides that the caller needs to perform some
@@ -212,7 +225,7 @@
if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
break;
- dirty_exceeded = 1;
+ node_dirty_exceeded = 1;
/* Note: nr_reclaimable denotes nr_dirty + nr_unstable.
* Unstable writes are a feature of certain networked
@@ -235,7 +248,7 @@
}
if (nr_reclaimable + wbs.nr_writeback <= dirty_thresh)
- dirty_exceeded = 0;
+ node_dirty_exceeded = 0;
if (writeback_in_progress(bdi))
return; /* pdflush is already working this queue */
@@ -272,7 +285,7 @@
long ratelimit;
ratelimit = ratelimit_pages;
- if (dirty_exceeded)
+ if (node_dirty_exceeded)
ratelimit = 8;
/*
-
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