Re: [PATCH 0/4] Improve swap page error handling

[Nick Piggin <nickpiggin@yahoo.com.au>]

Richard Purdie wrote:

> > No, not this way, I'm afraid.  Sorry, I don't remember the prior
> > discussion on LKML, must have flooded past when my attention was
> > elsewhere.
>
>
> I think you were cc'd on some of it but you never commented. Anyhow,
> I've reworked this patch series based on your comments. The hints were
> appreciated, thanks. This was the way I'd originally hoped to be able to
> work things, I just couldn't find the right way to do it.

IMO it seems a bit complex for so small a benefit. Last time I was
working on this, I thought it would be almost as good to do something
simple like stop trying to write out the page if PG_error is set (and
clear that bit in delete_from_swap_cache or try_to_unusesomewhere).
This way the admin could swapoff and scan the swap device at some
point.

> > Is it worth doing this at all?  Probably, but I've no experience
> > whatsoever of swap write errors, so it's hard for me to judge: my
> > guess is that many cases would turn out to be software errors (e.g.
> > lower level needing more memory to perform the write).  But you'd
> > be right to counter: let's assume they're hardware errors, and
> > then fix up any software errors when reported.
>
>
> I have a swap block driver where hardware write errors are more likely
> and hence have a need to handle them more gracefully than IO loops. It
> seems like a good idea to avoid the IO loops anyway.
>
>
> > If it is worth doing this, then you'll need to add code to write
> > back the swap header, to note the bad pages permanently: you may
> > well have been waiting to see what reception the patches so far
> > get, before embarking on that.
>
>
> You can't proceed to do that until you're able to identify the bad pages
> so this would be a necessary first step towards that, yes.

Agreed here, FWIW. I think that might be just as well done in
userspace?

Nick

--
SUSE Labs, Novell Inc.
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