Re: fsync delays for a long time.

[Andrew Morton]

Alan Cox wrote:
> 
> > > fsync on a very large file is very slow on the 2.2 kernels
> >
> > This could very well be due to request allocation starvation.
> > fsync is sleeping in __get_request_wait() while bonnie keeps
> > on stealing all the requests.
> 
> That may amplify it but in the 2.2 case fsync on any sensible sized file
> is already horribly performing. It hits databases like solid quite badly

I'm surprised.  ext2's fsync in 2.2 is in fact quite optimal: a single
pass across the block tree, in probable-LBA-order.  No livelock potential
there.  Optimal.  Note that it implements "only sync the stuff which was
dirty on entry" semantics.

But msync() is a different kettle of fish.  It calls file_fsync(), which
syncs the entire device, livelockably.  Are you sure `solid' is not
using msync?

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