On Wednesday 02 March 2011, at 07:41:00, <Andrew Morton [off-list ref]> wrote
On Sat, 26 Feb 2011 22:56:31 +0800
Nai Xia [off-list ref] wrote:

quoted

ksm_pages_sharing is updated by ksmd periodically.  In some cases, it cannot 
reflect the actual savings and makes the benchmarks on volatile VMAs very 
inaccurate.

This patch add a vm_stat entry and let the /proc/meminfo show information 
about how much virutal address pte is being mapped to ksm pages.  With default 
ksm paramters (pages_to_scan==100 && sleep_millisecs==20), this can result in 
50% more accurate averaged savings result for the following test program. 
Bigger sleep_millisecs values will increase this deviation. 

So I think you're saying that the existing ksm_pages_sharing sysfs file
is no good.

You added a new entry to /proc/meminfo and left ksm_pages_sharing
as-is.  Why not leave /proc/meminfo alone, and fix up the existing
ksm_pages_sharing?

The ksm_pages_sharing is really a count for how many "rmap_item"s is currently
linked in stable_nodes. ksmd updates ksm_pages_sharing whenever it's waken up.
However, just during the time ksmd is sleeping, many shared KSM pages can be 
broken because of page writes. So ksm_pages_sharing means much more an internal
state for ksm than a real count for how much pages is being shared at some time
point. Since the state of the internal data structures of ksm is only updated 
by ksmd privately. I think it's hard to make it correctly reflect the real time
memory saving. So I just added another count and let ksm_pages_sharing still 
focus on it original role.

Also, the patch accumulates the NR_KSM_PAGES_SHARING counts on a
per-zone basis as well as on a global basis, but only provides the
global count to userspace.  The per-zone counts are potentially
interesting?  If not, maintaining the per-zone counters is wasted
overhead.

Yes, I will make it to the zoneinfo, soon. 

quoted

--- test.c-----

The "^---" token conventionally means "end of changelog".  Please avoid
inserting it into the middle of the changelog.

OK, I understand now. :)

quoted

+++ b/mm/ksm.c

@@ -897,6 +897,7 @@ static int try_to_merge_one_page(struct vm_area_struct 

*vma,

Your email client wordwraps the patches.

Oops, sorry for the crappy client it is also responsible for my late reply.
I will fix it soon.

Nai

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