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authorChristoph Lameter <clameter@sgi.com>2006-09-26 02:31:52 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2006-09-26 11:48:51 -0400
commit0ff38490c836dc379ff7ec45b10a15a662f4e5f6 (patch)
treecb42d5d3cace3c8d12f0b304879039c503807981 /Documentation
parent972d1a7b140569084439a81265a0f15b74e924e0 (diff)
[PATCH] zone_reclaim: dynamic slab reclaim
Currently one can enable slab reclaim by setting an explicit option in /proc/sys/vm/zone_reclaim_mode. Slab reclaim is then used as a final option if the freeing of unmapped file backed pages is not enough to free enough pages to allow a local allocation. However, that means that the slab can grow excessively and that most memory of a node may be used by slabs. We have had a case where a machine with 46GB of memory was using 40-42GB for slab. Zone reclaim was effective in dealing with pagecache pages. However, slab reclaim was only done during global reclaim (which is a bit rare on NUMA systems). This patch implements slab reclaim during zone reclaim. Zone reclaim occurs if there is a danger of an off node allocation. At that point we 1. Shrink the per node page cache if the number of pagecache pages is more than min_unmapped_ratio percent of pages in a zone. 2. Shrink the slab cache if the number of the nodes reclaimable slab pages (patch depends on earlier one that implements that counter) are more than min_slab_ratio (a new /proc/sys/vm tunable). The shrinking of the slab cache is a bit problematic since it is not node specific. So we simply calculate what point in the slab we want to reach (current per node slab use minus the number of pages that neeed to be allocated) and then repeately run the global reclaim until that is unsuccessful or we have reached the limit. I hope we will have zone based slab reclaim at some point which will make that easier. The default for the min_slab_ratio is 5% Also remove the slab option from /proc/sys/vm/zone_reclaim_mode. [akpm@osdl.org: cleanups] 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.txt27
1 files changed, 20 insertions, 7 deletions
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 7cee90223d3a..20d0d797f539 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -29,6 +29,7 @@ Currently, these files are in /proc/sys/vm:
29- drop-caches 29- drop-caches
30- zone_reclaim_mode 30- zone_reclaim_mode
31- min_unmapped_ratio 31- min_unmapped_ratio
32- min_slab_ratio
32- panic_on_oom 33- panic_on_oom
33 34
34============================================================== 35==============================================================
@@ -138,7 +139,6 @@ This is value ORed together of
1381 = Zone reclaim on 1391 = Zone reclaim on
1392 = Zone reclaim writes dirty pages out 1402 = Zone reclaim writes dirty pages out
1404 = Zone reclaim swaps pages 1414 = Zone reclaim swaps pages
1418 = Also do a global slab reclaim pass
142 142
143zone_reclaim_mode is set during bootup to 1 if it is determined that pages 143zone_reclaim_mode is set during bootup to 1 if it is determined that pages
144from remote zones will cause a measurable performance reduction. The 144from remote zones will cause a measurable performance reduction. The
@@ -162,18 +162,13 @@ Allowing regular swap effectively restricts allocations to the local
162node unless explicitly overridden by memory policies or cpuset 162node unless explicitly overridden by memory policies or cpuset
163configurations. 163configurations.
164 164
165It may be advisable to allow slab reclaim if the system makes heavy
166use of files and builds up large slab caches. However, the slab
167shrink operation is global, may take a long time and free slabs
168in all nodes of the system.
169
170============================================================= 165=============================================================
171 166
172min_unmapped_ratio: 167min_unmapped_ratio:
173 168
174This is available only on NUMA kernels. 169This is available only on NUMA kernels.
175 170
176A percentage of the file backed pages in each zone. Zone reclaim will only 171A percentage of the total pages in each zone. Zone reclaim will only
177occur if more than this percentage of pages are file backed and unmapped. 172occur if more than this percentage of pages are file backed and unmapped.
178This is to insure that a minimal amount of local pages is still available for 173This is to insure that a minimal amount of local pages is still available for
179file I/O even if the node is overallocated. 174file I/O even if the node is overallocated.
@@ -182,6 +177,24 @@ The default is 1 percent.
182 177
183============================================================= 178=============================================================
184 179
180min_slab_ratio:
181
182This is available only on NUMA kernels.
183
184A percentage of the total pages in each zone. On Zone reclaim
185(fallback from the local zone occurs) slabs will be reclaimed if more
186than this percentage of pages in a zone are reclaimable slab pages.
187This insures that the slab growth stays under control even in NUMA
188systems that rarely perform global reclaim.
189
190The default is 5 percent.
191
192Note that slab reclaim is triggered in a per zone / node fashion.
193The process of reclaiming slab memory is currently not node specific
194and may not be fast.
195
196=============================================================
197
185panic_on_oom 198panic_on_oom
186 199
187This enables or disables panic on out-of-memory feature. If this is set to 1, 200This enables or disables panic on out-of-memory feature. If this is set to 1,