Re: [PATCH 1/2] swap: allow swap readahead to be merged

[Minchan Kim <minchan@kernel.org>]

On 05/21/2012 05:09 PM, ehrhardt@linux.vnet.ibm.com wrote:

> From: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
> 
> Swap readahead works fine, but the I/O to disk is almost always done in page
> size requests, despite the fact that readahead submits 1<<page-cluster pages
> at a time.
> On older kernels the old per device plugging behavior might have captured
> this and merged the requests, but currently all comes down to much more I/Os
> than required.
> 
> On a single device this might not be an issue, but as soon as a server runs
> on shared san resources savin I/Os not only improves swapin throughput but
> also provides a lower resource utilization.
> 
> With a load running KVM in a lot of memory overcommitment (the hot memory
> is 1.5 times the host memory) swapping throughput improves significantly
> and the lead feels more responsive as well as achieves more throughput.
> 
> In a test setup with 16 swap disks running blocktrace on one of those disks
> shows the improved merging:
> Prior:
> Reads Queued:     560,888,    2,243MiB  Writes Queued:     226,242,  904,968KiB
> Read Dispatches:  544,701,    2,243MiB  Write Dispatches:  159,318,  904,968KiB
> Reads Requeued:         0               Writes Requeued:         0
> Reads Completed:  544,716,    2,243MiB  Writes Completed:  159,321,  904,980KiB
> Read Merges:       16,187,   64,748KiB  Write Merges:       61,744,  246,976KiB
> IO unplugs:       149,614               Timer unplugs:       2,940
> 
> With the patch:
> Reads Queued:     734,315,    2,937MiB  Writes Queued:     300,188,    1,200MiB
> Read Dispatches:  214,972,    2,937MiB  Write Dispatches:  215,176,    1,200MiB
> Reads Requeued:         0               Writes Requeued:         0
> Reads Completed:  214,971,    2,937MiB  Writes Completed:  215,177,    1,200MiB
> Read Merges:      519,343,    2,077MiB  Write Merges:       73,325,  293,300KiB
> IO unplugs:       337,130               Timer unplugs:      11,184
> 
> Signed-off-by: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
> Acked-by: Rik van Riel <riel@redhat.com>
> Acked-by: Jens Axboe <axboe@kernel.dk>


Reviewed-by: Minchan Kim <minchan@kernel.org>

Didn't I add my Reviewed-by on your previous version?

-- 
Kind regards,
Minchan Kim

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