Re: [PATCH 0/2] swap: improve swap I/O rate

[Minchan Kim <minchan@kernel.org>]

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

> From: Ehrhardt Christian <ehrhardt@linux.vnet.ibm.com>
> 
> From: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
> 
> 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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