Re: [Xen-devel] Fatal crash on xen4.2 HVM + qemu-xen dm + NFS

[Alex Bligh <alex@xxxxxxxxxxx>]

Konrad,

--On 6 March 2013 20:01:53 -0500 Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 
wrote:

> > Results are positive.
> Great!
Does that mean some sort of switch to turn off O_DIRECT (or turning it off
by default) can go into qemu?

> Thought it is interesting that the application is doing write and sync
> (WS) for other blocks (like 2013633), which I thought would have
> been the case if the file was opened with O_SYNC. The sparsecopy
> code does not seem to do it?
On both host and guest every single write has 'S' set. You are correct that
sparsecopy doesn't open with O_SYNC. Perhaps it's the fact that it's the
fdatasync() which is causing the writes from the page cache (and that by
definition is blocking) which causes blktrace to see 'S' bits? I think it
was writing 4k blocks and syncing every 16k.

--
Alex Bligh

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