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authorChristoph Lameter <clameter@sgi.com>2006-07-03 00:24:13 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-07-03 15:26:59 -0700
commit9614634fe6a138fd8ae044950700d2af8d203f97 (patch)
tree9b020c1d36d8625f4048c057058efb2e17c81973 /Documentation
parentcb6358eb69d9854f65f2979c0ce9280eee041828 (diff)
[PATCH] ZVC/zone_reclaim: Leave 1% of unmapped pagecache pages for file I/O
It turns out that it is advantageous to leave a small portion of unmapped file backed pages if all of a zone's pages (or almost all pages) are allocated and so the page allocator has to go off-node. This allows recently used file I/O buffers to stay on the node and reduces the times that zone reclaim is invoked if file I/O occurs when we run out of memory in a zone. The problem is that zone reclaim runs too frequently when the page cache is used for file I/O (read write and therefore unmapped pages!) alone and we have almost all pages of the zone allocated. Zone reclaim may remove 32 unmapped pages. File I/O will use these pages for the next read/write requests and the unmapped pages increase. After the zone has filled up again zone reclaim will remove it again after only 32 pages. This cycle is too inefficient and there are potentially too many zone reclaim cycles. With the 1% boundary we may still remove all unmapped pages for file I/O in zone reclaim pass. However. it will take a large number of read and writes to get back to 1% again where we trigger zone reclaim again. The zone reclaim 2.6.16/17 does not show this behavior because we have a 30 second timeout. [akpm@osdl.org: rename the /proc file and the variable] Signed-off-by: Christoph Lameter <clameter@sgi.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/sysctl/vm.txt14
1 files changed, 14 insertions, 0 deletions
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 86754eb390d..7cee90223d3 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -28,6 +28,7 @@ Currently, these files are in /proc/sys/vm:
- block_dump
- drop-caches
- zone_reclaim_mode
+- min_unmapped_ratio
- panic_on_oom
==============================================================
@@ -168,6 +169,19 @@ in all nodes of the system.
=============================================================
+min_unmapped_ratio:
+
+This is available only on NUMA kernels.
+
+A percentage of the file backed pages in each zone. Zone reclaim will only
+occur if more than this percentage of pages are file backed and unmapped.
+This is to insure that a minimal amount of local pages is still available for
+file I/O even if the node is overallocated.
+
+The default is 1 percent.
+
+=============================================================
+
panic_on_oom
This enables or disables panic on out-of-memory feature. If this is set to 1,