On Fri, Apr 12, 2013 at 10:38:43PM +0900, Mitsuhiro Tanino wrote: > (2013/04/12 3:10), Andi Kleen wrote: > > On Thu, Apr 11, 2013 at 11:23:08AM -0400, 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 agree with Andi. We need to care both memory error and asynchronous > I/O error. > > >> 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. > > > > Not sure. Some of the current behavior may be dubious and it may > > be possible to change it. But would need more analysis. > > > > I don't think we're concerned that much about "correct" applications, > > but more ones that do not check everything. So returning more > > errors should be safer. > > > > For example you could have a sysctl that enables always stick > > IO error -- that keeps erroring until it is closed. > > > >> I'm working on a new pagecache tag based mechanism to solve this. > >> But it needs time and more discussions. > >> So I guess Tanino-san suggests giving up on dirty pagecache errors > >> as a quick solution. > > > > A quick solution would be enabling panic for any asynchronous IO error. > > I don't think the memory error code is the right point to hook into. > > Yes. I think both short term solution and long term solution is necessary > in order to enable hwpoison feature for Linux as KVM hypervisor. > > So my proposal is as follows, > For short term solution to care both memory error and I/O error: > - I will resend a panic knob to handle data lost related to dirty cache > which is caused by memory error and I/O error. Sorry, I still think "panic on dirty pagecache error" is feasible in userspace. This new knob will be completely useless after memory error reporting is fixed in the future, so whenever possible I like the userspace solution even for a short term one. Thanks, Naoya > For long term solution: > - Andi's proposal or Horiguchi-san's new pagecache tag based mechanism -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>