[PATCH] mm/hwpoison: dissolve error hugepages of file mapping

[PATCH] mm/hwpoison: dissolve error hugepages of file mapping

[Bin Wang]

We handle error on hugetlb file with hugetlbfs_error_remove_page(),
which removes the error hugepages from page cache. And with the
HWPoison flag in head page, it is safe to free the error hugepages
and dissolve it.

Fixes: 78bb920344b8a ("mm: hwpoison: dissolve in-use hugepage in unrecoverable memory error")
Signed-off-by: Bin Wang <wangbin224@huawei.com>
---
 mm/memory-failure.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index eefd823deb67..6a3c46b601ef 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -988,6 +988,13 @@ static int me_huge_page(struct page *p, unsigned long pfn)
 	if (mapping) {
 		res = truncate_error_page(hpage, pfn, mapping);
 		unlock_page(hpage);
+		if (ret == MF_RECOVERED) {
+			put_page(hpage);
+			if (__page_handle_poison(p))
+				page_ref_inc(p);
+			else
+				ret = MF_FAILED;
+		}
 	} else {
 		res = MF_FAILED;
 		unlock_page(hpage);
-- 
2.23.0

Re: [PATCH] mm/hwpoison: dissolve error hugepages of file mapping

[Matthew Wilcox]

On Thu, Jul 15, 2021 at 11:08:52PM +0800, Bin Wang wrote:
> We handle error on hugetlb file with hugetlbfs_error_remove_page(),
> which removes the error hugepages from page cache. And with the
> HWPoison flag in head page, it is safe to free the error hugepages
> and dissolve it.

How is that safe?  If you're going to dissolve the huge page, you
need to figure out which subpage needs to have the HWPoison flag set.

Re: Re: [PATCH] mm/hwpoison: dissolve error hugepages of file mapping

[Bin Wang]

Hi Matthew,

On Thu, 15 Jul 2021 at 16:22:40 +0100, Matthew Wilcox wrote:
> How is that safe?  If you're going to dissolve the huge page, you
> need to figure out which subpage needs to have the HWPoison flag set.

Thanks for your review. The p that we pass to the __page_handle_poison()
is the error subpage. And we will move the HWPoison flag to subpage in
the dissolve_free_huge_page():

if (PageHWPoison(head) && page != head) {
	SetPageHWPoison(page);
	ClearPageHWPoison(head);
}

Thanks,
Bin Wang