[CRIU] Soft dirty pages in expanded VMA

[Mike Rapoport]

On Mon, May 13, 2019 at 04:10:54PM -0700, Diyu Zhou wrote:
> Hey, 
> 
> Firstly, thanks for the great tool! It is very very helpful. I can see the
> development of such a tool 
> is very challenging and you guys do several clever tricks to make it possible.
> I enjoy a lot using 
> the tool as well as reading the source code and have learned a lot from it. 
> 
> I have a question regarding the implementation of the soft dirty pages. From
> what I can tell, if 
> a VMA is expanded, all the pages within it will be marked as soft dirty. This
> seems to me will 
> result in unnecessarily transferring clean pages when iterative dumps are
> performed. 
> Is there any reason not just mark the pages in the expanded part of the VMA
> soft dirty? 

When a VMA is expanded is is marked soft-dirty to ensure it would be
scanned for the dirty pages.
Each page has its own marking that says whether the page is dirty or not.
The per-page information is available at /proc/PID/pagemap and CRIU uses it
to actually decide what page should be dumped.
 
> Thanks again for the wonderful tool and your help! 
> 
> Best,
> Diyu
> 
> 
>  

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-- 
Sincerely yours,
Mike.