Re: [RFC Patch 0/2] mm: Add parameters to make kernel behavior at memory error on dirty cache selectable

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

On Wed, Apr 17, 2013 at 02:42:51PM +0800, Simon Jeons wrote:
> Hi Naoya,
> On 04/11/2013 11:23 PM, Naoya Horiguchi wrote:
> > On Thu, Apr 11, 2013 at 03:49:16PM +0200, Andi Kleen wrote:
> >>> As a result, if the dirty cache includes user data, the data is lost,
> >>> and data corruption occurs if an application uses old data.
> >> The application cannot use old data, the kernel code kills it if it
> >> would do that. And if it's IO data there is an EIO triggered.
> >>
> >> iirc the only concern in the past was that the application may miss
> >> the asynchronous EIO because it's cleared on any fd access. 
> >>
> >> This is a general problem not specific to memory error handling, 
> >> as these asynchronous IO errors can happen due to other reason
> >> (bad disk etc.) 
> >>
> >> If you're really concerned about this case I think the solution
> >> is to make the EIO more sticky so that there is a higher chance
> >> than it gets returned.  This will make your data much more safe,
> >> as it will cover all kinds of IO errors, not just the obscure memory
> >> errors.
> > I'm interested in this topic, and in previous discussion, what I was said
> > is that we can't expect user applications to change their behaviors when
> > they get EIO, so globally changing EIO's stickiness is not a great approach.
> 
> The user applications will get EIO firstly or get SIG_KILL firstly?

That depends on how the process accesses to the error page, so I can't
say which one comes first.

Thanks,
Naoya Horiguchi