[linux-mm-cc] I guess you have been following ksm.

[Peter Dolding]

http://lkml.org/lkml/2009/4/16/300

ksm is using Linux copy on write system to merge pages.   compcache
currently takes page into swap virtual swap yes it costs no space but
it costing cpu time to get it back.   With blank pages in particular
it would be better not to.  Instead exploit the copy on write system
and connect all blank pages to the same memory block marked read only.
 When the memory page needs re accessing it will not have to be pulled
back from swap since it never really left.

The copy on write system also appears to provide something else
interesting.  ksm and compcache are both after allocation.   The
interesting question is if Linux kernel should provide a calloc
function.   So that on commit its is automatically stacked.  This
would massively reduce the numbers of blank matching pages.  Linux
system already has something that deals with malloc allowing over
commits until accessed.

compcache is useful so far ramzswap.   Support for a disk based zswap
could also be a god send.  Disk transfer speeds are limited.

There are many ways to get more applications into memory.  Looking at
the other end when memory is allocated and where application is loaded
into memory could provide savings without cost.

Lets take a executable with a stack of pages the same.  Scanning tool
run over it locate the pages that can be stacked make executable
smaller have loader automatically join those pages up.   Remember
Linux does not send applications to swap.  Instead deallocates the
page and reads it back from executable file.   Swap only gets
application created data.

There are still a lot of areas with memory Linux can do better.
Looking at targeting on commit saves cpu time since.   Restoring
duplicate pages using copy on write also saves on cpu time.  Merging
page duplicates instead of going into swap also saves cpu time.   More
pages in memory less swap system access.  Just compress everything
sent to swap is not the best solution for cpu time used.  Sending ram
to disk based swap is not the best solution either.   Goal need to be
use swap less and giving more data in memory the cpu can access.
There is no point having zswap if executables are still being cleared
from memory using disk.

Peter Dolding