The patch titled
Subject: documentation: update how page-cluster affects swap I/O
has been added to the -mm tree. Its filename is
documentation-update-how-page-cluster-affects-swap-i-o.patch
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------------------------------------------------------
From: Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxxxxxxx>
Acked-by: Jens Axboe <axboe@xxxxxxxxx>
Reviewed-by: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/sysctl/vm.txt | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff -puN Documentation/sysctl/vm.txt~documentation-update-how-page-cluster-affects-swap-i-o Documentation/sysctl/vm.txt
--- a/Documentation/sysctl/vm.txt~documentation-update-how-page-cluster-affects-swap-i-o
+++ a/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
_
Subject: Subject: documentation: update how page-cluster affects swap I/O
Patches currently in -mm which might be from ehrhardt@xxxxxxxxxxxxxxxxxx are
swap-allow-swap-readahead-to-be-merged.patch
documentation-update-how-page-cluster-affects-swap-i-o.patch
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