Re: [RFC] madvise(MADV_TRUNCATE)

[Badari Pulavarty <pbadari@us.ibm.com>]

Jeff Dike wrote:

> On Wed, Oct 26, 2005 at 03:49:55PM -0700, Badari Pulavarty wrote:
> 
>>Basically, I added "truncate_range" inode operation to provide
>>opportunity for the filesystem to zero the blocks and/or free
>>them up. 
>>
>>I also attempted to implement shmem_truncate_range() which 
>>needs lots of testing before I work out bugs :(
> 
> 
> I added memory hotplug to UML to check this out.  It seems to be freeing
> pages that are outside the desired range.  I'm doing the simplest possible
> thing - grabbing a bunch of pages that are most likely not dirty yet, 
> and MADV_TRUNCATEing them one at a time.  Everything in UML goes harwire
> after that, and the cases that I've looked at involve pages being suddenly
> zero.
> 
> UML isn't exactly a minimal test case, but I'll give you what you need
> to reproduce this if you want.
> 

I cut-n-pasted shmem_truncate_range() from shmem_truncate() and fixed
few obvious things. Its very likely that, I missed whole bunch of changes.

My touch tests so far, doesn't really verify data after freeing. I was
thinking about writing cases. If I can use UML to do it, please send it
to me. I would rather test with real world case :)

Thanks,
Badari


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