Re: [Xen-devel] [PATCH] xenpaging:add a new array to speed up page-in in xenpaging

[Olaf Hering <olaf@xxxxxxxxx>]

On Thu, Jan 05, hongkaixing@xxxxxxxxxx wrote:

> # HG changeset patch
> # User hongkaixing<hongkaixing@xxxxxxxxxx>
> # Date 1325149704 -28800
> # Node ID 052727b8165ce6e05002184ae894096214c8b537
> # Parent  54a5e994a241a506900ee0e197bb42e5f1d8e759
> xenpaging:add a new array to speed up page-in in xenpaging
> 
> This patch adds a new array named page_out_index to reserve the victim's 
> index.
> When page in a page,it has to go through a for loop from 0 to num_pages to 
> find
> the right page to read,and it costs much time in this loop.After adding the
> page_out_index array,it just reads the arrry to get the right page,and saves 
> much time.
> 
> The following is a xenpaging test on suse11-64 with 4G memories.
> 
> Nums of page_out pages        Page out time   Page in time(in unstable code) 
> Page in time(apply this patch)
> 512M(131072)              2.6s                           540s                 
>              530s
> 2G(524288)                15.5s                          2088s                
>              2055s

Thanks for your work on this.

Is the page-out time for 512M really that fast? For me page-out is still
really slow even when the pagefile is in tmpfs. It takes several
minutes, I get around 4MB/s. page-in is around 20MB/s.

Wether an extra array is needed, we have to decide as it costs some
runtime memory. I was thinking already about better bitop functions,
like xc_find_next_bit_set and similar, just what xenpaging needs, to
remove the test bits one-by-one.

As for the new page-in op, there was some offline discussion about doing
page-in/page-out differently. If these ideas make into xen-unstable most
of domctls will disappear, and also the mmap to trigger page-in is not
needed anymore.

Olaf

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