Re: [Xen-devel] RE: Window VM hit blue screen when dom0 uses ext4 with extent enabled

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2011-07-14 at 06:44 +0100, MaoXiaoyun wrote:
> I think the 2.6.32.36 ext4 needs to backport this patch much likely.
> Otherwise it will hit the problem I met.
>  
> http://patchwork.ozlabs.org/patch/79880/

That version is still in state NEW but something appears to have been
committed upstream as e9e3bcecf44c04b9e6b505fd8e2eb9cea58fb94d:

    ext4: serialize unaligned asynchronous DIO
    
    ext4 has a data corruption case when doing non-block-aligned
    asynchronous direct IO into a sparse file, as demonstrated
    by xfstest 240.
    
    ...

Seems like a reasonable enough thing to backport to me (for what that's
worth). Although:
                            It is also quite a lot slower
    (14 min for package installs, vs. 8 min for well-aligned)
    but I'll take slow correctness over fast corruption any day.
    
    Mingming suggested that we can track outstanding
    conversions, and wait on those so that non-sparse
    files won't be affected, and I've implemented that here;
    unaligned AIO to nonsparse files won't take a perf hit.

Something to bear in mind if you are deploying anything based on sparse
files on ext4.

Ian.




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