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

[Andrew Morton <akpm@osdl.org>]

On Fri, 27 Oct 2006 08:59:55 +0100
Richard Purdie <rpurdie@openedhand.com> wrote:

> Fix handling of write failures to swap devices.
> 
> Calling SetPageError(page) marks the data in memory as bad and processes using
> the page in question will die unexpectedly. This isn't necessary as the data 
> in the memory page is still valid, just the copy on disk isn't. This patch 
> therefore removes this call.
> 
> Setting set_page_dirty(page) is good as the memory page will be retained and 
> processes don't die. It will try to write out the page again soon but a second 
> attempt at a write is probably no more likely to succeed than the first 
> resulting in IO loops. We can do better.
> 
> This patch attempts to unuse the page in a similar manner to swapoff. If 
> successful, mark the swap page as bad and remove it from use. If we fail to
> remove all references, we fall back on set_page_dirty above which will retry 
> the write.
> 
> If we can mark the swap page as bad, adjust the VM accounting to reflect this.
> 

Sounds like a reasonable approach.  Please copy Hugh (our lead swapoff maintainer)
on this work.

How was this tested?