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SubjectRe: [PATCH 11/15] HWPOISON: The high level memory error handler in the VM v8
On Sun, Jun 21, 2009 at 04:57:21PM +0800, Andi Kleen wrote:
> > v8:
> > check for page_mapped_in_vma() on anon pages (Hugh, Fengguang)
>
> This change was no good as discussed earlier.
>
> > test and use page->mapping instead of page_mapping() (Fengguang)
> > cleanup some early kill comments (Fengguang)
>
> This stuff belongs into the manpage. I haven't written it yet,
> but will. I don't think kernel source comments is the right place.

OK. You may take this block

+ * When the corrupted page data is not recoverable, the tasks mapped the page
+ * have to be killed. We offer two kill options:
+ * - early kill with SIGBUS.BUS_MCEERR_AO (optional)
+ * - late kill with SIGBUS.BUS_MCEERR_AR (mandatory)
+ * A task will be early killed as soon as corruption is found in its virtual
+ * address space, if it has called prctl(PR_MEMORY_FAILURE_EARLY_KILL, 1, ...);
+ * Any task will be late killed when it tries to access its corrupted virtual
+ * address. The early kill option offers KVM or other apps with large caches an
+ * opportunity to isolate the corrupted page from its internal cache, so as to
+ * avoid being late killed.

and/or this one into the man page :)

+=============================================================
+
+memory_failure_early_kill:
+
+Control how to kill processes when uncorrected memory error (typically
+a 2bit error in a memory module) is detected in the background by hardware
+that cannot be handled by the kernel. In some cases (like the page
+still having a valid copy on disk) the kernel will handle the failure
+transparently without affecting any applications. But if there is
+no other uptodate copy of the data it will kill to prevent any data
+corruptions from propagating.
+
+1: Kill all processes that have the corrupted and not reloadable page mapped
+as soon as the corruption is detected. Note this is not supported
+for a few types of pages, like kernel internally allocated data or
+the swap cache, but works for the majority of user pages.
+
+0: Only unmap the corrupted page from all processes and only kill a process
+who tries to access it.
+
+The kill is done using a catchable SIGBUS with BUS_MCEERR_AO, so processes can
+handle this if they want to.
+
+This is only active on architectures/platforms with advanced machine
+check handling and depends on the hardware capabilities.
+
==============================================================


But I think these new comments are OK?

+ * We don't aim to rescue 100% corruptions. That's unreasonable goal - the
+ * kernel text and slab pages (including the big dcache/icache) are almost
+ * impossible to isolate. We also try to keep the code clean by ignoring the
+ * other thousands of small corruption windows.
+ *

And this:

@@ -275,6 +286,12 @@ static void collect_procs_file(struct pa

vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff,
pgoff)
+ /*
+ * Send early kill signal to tasks whose vma covers
+ * the page but not necessarily mapped it in its pte.
+ * Applications who requested early kill normally want
+ * to be informed of such data corruptions.
+ */
if (vma->vm_mm == tsk->mm)
add_to_kill(tsk, page, vma, to_kill, tkc);
}
> > introduce invalidate_inode_page() and don't remove dirty/writeback pages
> > from page cache (Nick, Fengguang)
>
> I'm still dubious this is a good idea, it means potentially a lot
> of pages not covered.

This is good for .31 I think. But for .32 we can sure cover more pages :)

Thanks,
Fengguang


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