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| author | Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com> | 2012-07-31 16:41:46 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-07-31 18:42:39 -0700 |
| commit | df858fa8276f85106f2f5c3cd49c1fa524058070 (patch) | |
| tree | 7fd01b6311ae03f9f2d2aec5c73280ec925b254f /Documentation | |
| parent | 3fb5c298b04eb6e472f8db1f0fb472749d30041c (diff) | |
| download | kernel-common-df858fa8276f85106f2f5c3cd49c1fa524058070.tar.gz kernel-common-df858fa8276f85106f2f5c3cd49c1fa524058070.tar.bz2 kernel-common-df858fa8276f85106f2f5c3cd49c1fa524058070.zip | |
documentation: update how page-cluster affects swap I/O
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 <ehrhardt@linux.vnet.ibm.com>
Acked-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Minchan Kim <minchan@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | 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 96f0ee825bed..84eb25cd69aa 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 |