Re: [PATCH 2/2 v2] mm: print out information of file affected by memory error

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

On Mon, Nov 05, 2012 at 02:01:54PM -0800, Andrew Morton wrote:
> On Fri,  2 Nov 2012 12:33:13 -0400
> Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> wrote:
> 
> > Printing out the information about which file can be affected by a
> > memory error in generic_error_remove_page() is helpful for user to
> > estimate the impact of the error.
> > 
> > Changelog v2:
> >   - dereference mapping->host after if (!mapping) check for robustness
> > 
> > ...
> >
> > --- v3.7-rc3.orig/mm/truncate.c
> > +++ v3.7-rc3/mm/truncate.c
> > @@ -151,14 +151,20 @@ int truncate_inode_page(struct address_space *mapping, struct page *page)
> >   */
> >  int generic_error_remove_page(struct address_space *mapping, struct page *page)
> >  {
> > +	struct inode *inode;
> > +
> >  	if (!mapping)
> >  		return -EINVAL;
> > +	inode = mapping->host;
> >  	/*
> >  	 * Only punch for normal data pages for now.
> >  	 * Handling other types like directories would need more auditing.
> >  	 */
> > -	if (!S_ISREG(mapping->host->i_mode))
> > +	if (!S_ISREG(inode->i_mode))
> >  		return -EIO;
> > +	pr_info("MCE %#lx: file info pgoff:%lu, inode:%lu, dev:%s\n",
> > +		page_to_pfn(page), page_index(page),
> > +		inode->i_ino, inode->i_sb->s_id);
> >  	return truncate_inode_page(mapping, page);
> >  }
> >  EXPORT_SYMBOL(generic_error_remove_page);
> 
> A couple of things.
> 
> - I worry that if a hardware error occurs, it might affect a large
>   amount of memory all at the same time.  For example, if a 4G memory
>   block goes bad, this message will be printed a million times?

If the error on 4G memory block triggered by SRAO MCE and these 1M pages
are all pagecache pages, the answer is yes.
But I think that if it's a whole DIMM error, it should be reported by
another type of MCE than SRAO, so printing a million times seems to be
unlikely to happen.

> - hard-wiring "MCE" in here seems a bit of a layering violation? 
>   What right does the generic, core .error_remove_page() implementation
>   have to assume that it was called because of an MCE?

OK, we need not assume that. I change "MCE " prefix to more specific
one like "Memory error ".

> Many CPU types don't eveh have such a thing?

No. At least currently, only SRAO MCE triggers memory_failure() and
it's defined only on some newest highend models of Intel CPUs.

Thanks,
Naoya

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