Re: [PATCH, RFC/T] Fix handling of write failures to swap devices

[Nick Piggin]

Richard Purdie wrote:
> On Sat, 2006-10-28 at 22:10 +1000, Nick Piggin wrote: 

> > That isn't your only problem though, and we simply don't want to do
> > this (potentially expensive) unusing from interrupt context. Noting
> > the error and dealing with it in process context I think is the best
> > way to do it.
>
>
> The reasoning was that this circumstance should be extremely rare. If it
> happens, we have a hardware problem. Recovering from that hardware
> problem gracefully is more important than a slightly longer interrupt.
> But yes, process context would be nicer, *if* we can find a way to do
> it. 

Also note that the current code *should* "gracefully" handle the failure.
In that, it will not reclaim the page on a write error, so it isn't going
to cause a data loss...

It's just that it currently results in unswappable pages.

Handling it more gracefully by allowing the page to be retried with another
swap entry is OK I guess, but given the added complexity, I'm not even sure
it is worthwhile.

Perhaps we should just do the ClearPageError in the try_to_unuse path,
because the sysadmin should take down that swap device on failure. So if a
new device is added, we want to be able to unpin the failed pages.

--
SUSE Labs, Novell Inc.
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