[PATCH 2/2] documentation: update how page-cluster affects swap I/O
From: <hidden>
Date: 2012-06-04 08:34:05
Subsystem:
documentation, the rest · Maintainers:
Jonathan Corbet, Linus Torvalds
From: Christian Ehrhardt <redacted> Fix of the documentation of /proc/sys/vm/page-cluster to match the behavior of the code and add some comments about what the tunable will change in that behavior. Signed-off-by: Christian Ehrhardt <redacted> Acked-by: Jens Axboe <axboe@kernel.dk> Reviewed-by: Minchan Kim <minchan@kernel.org> --- Documentation/sysctl/vm.txt | 12 ++++++++++-- 1 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 96f0ee8..4d87dc0 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt@@ -574,16 +574,24 @@ of physical RAM. See above. page-cluster -page-cluster controls the number of pages which are written to swap in -a single attempt. The swap I/O size. +page-cluster controls the number of pages up to which consecutive pages +are read in from swap in a single attempt. This is the swap counterpart +to page cache readahead. +The mentioned consecutivity is not in terms of virtual/physical addresses, +but consecutive on swap space - that means they were swapped out together. It is a logarithmic value - setting it to zero means "1 page", setting it to 1 means "2 pages", setting it to 2 means "4 pages", etc. +Zero disables swap readahead completely. The default value is three (eight pages at a time). There may be some small benefits in tuning this to a different value if your workload is swap-intensive. +Lower values mean lower latencies for initial faults, but at the same time +extra faults and I/O delays for following faults if they would have been part of +that consecutive pages readahead would have brought in. + ============================================================= panic_on_oom
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1.7.0.4
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