On 05/14/2012 08:58 PM, ehrhardt@linux.vnet.ibm.com wrote:

From: Ehrhardt Christian <redacted>

From: Christian Ehrhardt <redacted>

In an memory overcommitment scneario with KVM I ran into a lot of wiats for
swap. While checking the I/O done on the swap disks I found almost all I/Os
to be done as single page 4k request. Despite the fact that swap in is a
batch of 1<<page-cluster pages as swap readahead and swap out is a list of
pages written in shrink_page_list.

[1/2 swap in improvment]
The read patch shows improvements of up to 50% swap throughput, much happier
guest systems and even when running with comparable throughput a lot I/O per
seconds saved leaving resources in the SAN for other consumers.

[2/2 documentation]
While doing so I also realized that the documentation for
proc/sys/vm/page-cluster is no more matching the code

[missing patch #3]
I tried to get a similar patch working for swap out in shrink_page_list. And
it worked in functional terms, but the additional mergin was negligible.

I think we have already done it.
Look at shrink_mem_cgroup_zone which ends up calling shrink_page_list so we already have applied
I/O plugging. 

Maybe the cond_resched triggers much mor often than I expected, I'm open for
suggestions regarding improving the pagout I/O sizes as well.

We could enhance write out by batch like ext4_bio_write_page.

Kind regards,
Christian Ehrhardt


Christian Ehrhardt (2):
  swap: allow swap readahead to be merged
  documentation: update how page-cluster affects swap I/O

 Documentation/sysctl/vm.txt |   12 ++++++++++--
 mm/swap_state.c             |    5 +++++
 2 files changed, 15 insertions(+), 2 deletions(-)

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Kind regards,
Minchan Kim

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