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ksm: more on default values

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Adjust the max_kernel_pages default to a quarter of totalram_pages,
instead of nr_free_buffer_pages() / 4: the KSM pages themselves come from
highmem, and even on a 16GB PAE machine, 4GB of KSM pages would only be
pinning 32MB of lowmem with their rmap_items, so no need for the more
obscure calculation (nor for its own special init function).

There is no way for the user to switch KSM on if CONFIG_SYSFS is not
enabled, so in that case default run to KSM_RUN_MERGE.

Update KSM Documentation and Kconfig to reflect the new defaults.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2009-10-07 16:32:22 -07:00 • committed by Linus Torvalds
parent 0eca52a927
commit c73602ad31
3 changed files with 14 additions and 13 deletions
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13
Documentation/vm/ksm.txt
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@ -52,15 +52,15 @@ The KSM daemon is controlled by sysfs files in /sys/kernel/mm/ksm/,
readable by all but writable only by root:
max_kernel_pages - set to maximum number of kernel pages that KSM may use
e.g. "echo 2000 > /sys/kernel/mm/ksm/max_kernel_pages"
e.g. "echo 100000 > /sys/kernel/mm/ksm/max_kernel_pages"
Value 0 imposes no limit on the kernel pages KSM may use;
but note that any process using MADV_MERGEABLE can cause
KSM to allocate these pages, unswappable until it exits.
Default: 2000 (chosen for demonstration purposes)
Default: quarter of memory (chosen to not pin too much)
pages_to_scan - how many present pages to scan before ksmd goes to sleep
e.g. "echo 200 > /sys/kernel/mm/ksm/pages_to_scan"
Default: 200 (chosen for demonstration purposes)
e.g. "echo 100 > /sys/kernel/mm/ksm/pages_to_scan"
Default: 100 (chosen for demonstration purposes)
sleep_millisecs - how many milliseconds ksmd should sleep before next scan
e.g. "echo 20 > /sys/kernel/mm/ksm/sleep_millisecs"
@ -70,7 +70,8 @@ run - set 0 to stop ksmd from running but keep merged pages,
set 1 to run ksmd e.g. "echo 1 > /sys/kernel/mm/ksm/run",
set 2 to stop ksmd and unmerge all pages currently merged,
but leave mergeable areas registered for next run
Default: 1 (for immediate use by apps which register)
Default: 0 (must be changed to 1 to activate KSM,
except if CONFIG_SYSFS is disabled)
The effectiveness of KSM and MADV_MERGEABLE is shown in /sys/kernel/mm/ksm/:
@ -86,4 +87,4 @@ pages_volatile embraces several different kinds of activity, but a high
proportion there would also indicate poor use of madvise MADV_MERGEABLE.
Izik Eidus,
Hugh Dickins, 30 July 2009
Hugh Dickins, 24 Sept 2009