On 2022/7/8 13:36, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
>
> When handling memory error on a hugetlb page, the error handler tries to
> dissolve and turn it into 4kB pages. If it's successfully dissolved,
> PageHWPoison flag is moved to the raw error page, so that's all right.
> However, dissolve sometimes fails, then the error page is left as
> hwpoisoned hugepage. It's useful if we can retry to dissolve it to save
> healthy pages, but that's not possible now because the information about
> where the raw error pages is lost.
>
> Use the private field of a few tail pages to keep that information. The
> code path of shrinking hugepage pool uses this info to try delayed dissolve.
> In order to remember multiple errors in a hugepage, a singly-linked list
> originated from SUBPAGE_INDEX_HWPOISON-th tail page is constructed. Only
> simple operations (adding an entry or clearing all) are required and the
> list is assumed not to be very long, so this simple data structure should
> be enough.
>
> If we failed to save raw error info, the hwpoison hugepage has errors on
> unknown subpage, then this new saving mechanism does not work any more,
> so disable saving new raw error info and freeing hwpoison hugepages.
>
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> ---
> v4 -> v5:
> - fixed build error (reported by kernel test robot).
> - do not try to undo remove_hugetlb_page() when HPageRawHwpUnreliable is true,
> - check HPageRawHwpUnreliable() before hugetlb_vmemmap_restore(),
> - call num_poisoned_pages_inc() in hugetlb_set_page_hwpoison() when kalloc
> succeeds,
> - remove "inline" in the definition of hugetlb_clear_page_hwpoison().
>
> v3 -> v4:
> - resolve conflict with "mm: hugetlb_vmemmap: improve hugetlb_vmemmap
> code readability", use hugetlb_vmemmap_restore() instead of
> hugetlb_vmemmap_alloc().
>
> v2 -> v3:
> - remove duplicate "return ret" lines,
> - use GFP_ATOMIC instead of GFP_KERNEL,
> - introduce HPageRawHwpUnreliable pseudo flag (suggested by Muchun),
> - hugetlb_clear_page_hwpoison removes raw_hwp_page list even if
> HPageRawHwpUnreliable is true, (by Miaohe)
>
> v1 -> v2:
> - support hwpoison hugepage with multiple errors,
> - moved the new interface functions to mm/memory-failure.c,
> - define additional subpage index SUBPAGE_INDEX_HWPOISON_UNRELIABLE,
> - stop freeing/dissolving hwpoison hugepages with unreliable raw error info,
> - drop hugetlb_clear_page_hwpoison() in dissolve_free_huge_page() because
> that's done in update_and_free_page(),
> - move setting/clearing PG_hwpoison flag to the new interfaces,
> - checking already hwpoisoned or not on a subpage basis.
>
> ChangeLog since previous post on 4/27:
> - fixed typo in patch description (by Miaohe)
> - fixed config value in #ifdef statement (by Miaohe)
> - added sentences about "multiple hwpoison pages" scenario in patch
> description
> ---
> include/linux/hugetlb.h | 18 +++++++++-
> mm/hugetlb.c | 32 ++++++++++++-----
> mm/memory-failure.c | 79 +++++++++++++++++++++++++++++++++++++++--
> 3 files changed, 116 insertions(+), 13 deletions(-)
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 6d0620edf0a6..6fd128b80d57 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -42,6 +42,9 @@ enum {
> SUBPAGE_INDEX_CGROUP, /* reuse page->private */
> SUBPAGE_INDEX_CGROUP_RSVD, /* reuse page->private */
> __MAX_CGROUP_SUBPAGE_INDEX = SUBPAGE_INDEX_CGROUP_RSVD,
> +#endif
> +#ifdef CONFIG_MEMORY_FAILURE
> + SUBPAGE_INDEX_HWPOISON,
> #endif
> __NR_USED_SUBPAGE,
> };
> @@ -551,7 +554,7 @@ generic_hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
> * Synchronization: Initially set after new page allocation with no
> * locking. When examined and modified during migration processing
> * (isolate, migrate, putback) the hugetlb_lock is held.
> - * HPG_temporary - - Set on a page that is temporarily allocated from the buddy
> + * HPG_temporary - Set on a page that is temporarily allocated from the buddy
> * allocator. Typically used for migration target pages when no pages
> * are available in the pool. The hugetlb free page path will
> * immediately free pages with this flag set to the buddy allocator.
> @@ -561,6 +564,8 @@ generic_hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
> * HPG_freed - Set when page is on the free lists.
> * Synchronization: hugetlb_lock held for examination and modification.
> * HPG_vmemmap_optimized - Set when the vmemmap pages of the page are freed.
> + * HPG_raw_hwp_unreliable - Set when the hugetlb page has a hwpoison sub-page
> + * that is not tracked by raw_hwp_page list.
> */
> enum hugetlb_page_flags {
> HPG_restore_reserve = 0,
> @@ -568,6 +573,7 @@ enum hugetlb_page_flags {
> HPG_temporary,
> HPG_freed,
> HPG_vmemmap_optimized,
> + HPG_raw_hwp_unreliable,
> __NR_HPAGEFLAGS,
> };
>
> @@ -614,6 +620,7 @@ HPAGEFLAG(Migratable, migratable)
> HPAGEFLAG(Temporary, temporary)
> HPAGEFLAG(Freed, freed)
> HPAGEFLAG(VmemmapOptimized, vmemmap_optimized)
> +HPAGEFLAG(RawHwpUnreliable, raw_hwp_unreliable)
>
> #ifdef CONFIG_HUGETLB_PAGE
>
> @@ -796,6 +803,15 @@ extern int dissolve_free_huge_page(struct page *page);
> extern int dissolve_free_huge_pages(unsigned long start_pfn,
> unsigned long end_pfn);
>
> +#ifdef CONFIG_MEMORY_FAILURE
> +extern int hugetlb_clear_page_hwpoison(struct page *hpage);
> +#else
> +static inline int hugetlb_clear_page_hwpoison(struct page *hpage)
> +{
> + return 0;
> +}
> +#endif
> +
> #ifdef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
> #ifndef arch_hugetlb_migration_supported
> static inline bool arch_hugetlb_migration_supported(struct hstate *h)
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 77119d93a0f9..3956494cc5fb 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1442,6 +1442,15 @@ static void __remove_hugetlb_page(struct hstate *h, struct page *page,
> h->surplus_huge_pages_node[nid]--;
> }
>
> + /*
> + * This leaves HPageRawHwpUnreliable pages as leaked hugepages, not
> + * as leaked generic-compound pages. Otherwise page_mapped() or
> + * folio_mapped() gets slow because for-loop for each subpage is
> + * called.
> + */
> + if (HPageRawHwpUnreliable(page))
> + return;
> +
This patch looks good to me with below several possible problems:
Should "nr_huge_pages" and "nr_huge_pages_node" be adjusted too? If it's called from dissolve_free_huge_page
and hugetlb_vmemmap_restore fails, add_hugetlb_page will be called:
add_hugetlb_page:
...
h->nr_huge_pages++;
h->nr_huge_pages_node[nid]++;
^^^^^^^^1. the "nr_huge_pages" and "nr_huge_pages_node" might be incorrect?
...
zeroed = put_page_testzero(page);
^^^^^^^^2. VM_BUG_ON_PAGE(page_ref_count(page) == 0, page); will be triggered?
Or am I miss something?
Thanks!
> /*
> * Very subtle
> *
> @@ -1535,6 +1544,13 @@ static void __update_and_free_page(struct hstate *h, struct page *page)
> if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
> return;
>
> + /*
> + * If we don't know which subpages are hwpoisoned, we can't free
> + * the hugepage, so it's leaked intentionally.
> + */
> + if (HPageRawHwpUnreliable(page))
> + return;
> +
> if (hugetlb_vmemmap_restore(h, page)) {
> spin_lock_irq(&hugetlb_lock);
> /*
> @@ -1547,6 +1563,13 @@ static void __update_and_free_page(struct hstate *h, struct page *page)
> return;
> }
>
> + /*
> + * Move PageHWPoison flag from head page to the raw error pages,
> + * which makes any healthy subpages reusable.
> + */
> + if (unlikely(PageHWPoison(page)))
> + hugetlb_clear_page_hwpoison(page);
> +
> for (i = 0; i < pages_per_huge_page(h);
> i++, subpage = mem_map_next(subpage, page, i)) {
> subpage->flags &= ~(1 << PG_locked | 1 << PG_error |
> @@ -2109,15 +2132,6 @@ int dissolve_free_huge_page(struct page *page)
> */
> rc = hugetlb_vmemmap_restore(h, head);
> if (!rc) {
> - /*
> - * Move PageHWPoison flag from head page to the raw
> - * error page, which makes any subpages rather than
> - * the error page reusable.
> - */
> - if (PageHWPoison(head) && page != head) {
> - SetPageHWPoison(page);
> - ClearPageHWPoison(head);
> - }
> update_and_free_page(h, head, false);
> } else {
> spin_lock_irq(&hugetlb_lock);
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index c9931c676335..6833c5e4b410 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1664,6 +1664,80 @@ int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
> EXPORT_SYMBOL_GPL(mf_dax_kill_procs);
> #endif /* CONFIG_FS_DAX */
>
> +#ifdef CONFIG_HUGETLB_PAGE
> +/*
> + * Struct raw_hwp_page represents information about "raw error page",
> + * constructing singly linked list originated from ->private field of
> + * SUBPAGE_INDEX_HWPOISON-th tail page.
> + */
> +struct raw_hwp_page {
> + struct llist_node node;
> + struct page *page;
> +};
> +
> +static inline struct llist_head *raw_hwp_list_head(struct page *hpage)
> +{
> + return (struct llist_head *)&page_private(hpage + SUBPAGE_INDEX_HWPOISON);
> +}
> +
> +static int hugetlb_set_page_hwpoison(struct page *hpage, struct page *page)
> +{
> + struct llist_head *head;
> + struct raw_hwp_page *raw_hwp;
> + struct llist_node *t, *tnode;
> + int ret = TestSetPageHWPoison(hpage) ? -EHWPOISON : 0;
> +
> + /*
> + * Once the hwpoison hugepage has lost reliable raw error info,
> + * there is little meaning to keep additional error info precisely,
> + * so skip to add additional raw error info.
> + */
> + if (HPageRawHwpUnreliable(hpage))
> + return -EHWPOISON;
> + head = raw_hwp_list_head(hpage);
> + llist_for_each_safe(tnode, t, head->first) {
> + struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node);
> +
> + if (p->page == page)
> + return -EHWPOISON;
> + }
> +
> + raw_hwp = kmalloc(sizeof(struct raw_hwp_page), GFP_ATOMIC);
> + if (raw_hwp) {
> + raw_hwp->page = page;
> + llist_add(&raw_hwp->node, head);
> + /* the first error event will be counted in action_result(). */
> + if (ret)
> + num_poisoned_pages_inc();
> + } else {
> + /*
> + * Failed to save raw error info. We no longer trace all
> + * hwpoisoned subpages, and we need refuse to free/dissolve
> + * this hwpoisoned hugepage.
> + */
> + SetHPageRawHwpUnreliable(hpage);
> + }
> + return ret;
> +}
> +
> +int hugetlb_clear_page_hwpoison(struct page *hpage)
> +{
> + struct llist_head *head;
> + struct llist_node *t, *tnode;
> +
> + if (!HPageRawHwpUnreliable(hpage))
> + ClearPageHWPoison(hpage);
> + head = raw_hwp_list_head(hpage);
> + llist_for_each_safe(tnode, t, head->first) {
> + struct raw_hwp_page *p = container_of(tnode, struct raw_hwp_page, node);
> +
> + SetPageHWPoison(p->page);
> + kfree(p);
> + }
> + llist_del_all(head);
> + return 0;
> +}
> +
> /*
> * Called from hugetlb code with hugetlb_lock held.
> *
> @@ -1698,7 +1772,7 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags)
> goto out;
> }
>
> - if (TestSetPageHWPoison(head)) {
> + if (hugetlb_set_page_hwpoison(head, page)) {
> ret = -EHWPOISON;
> goto out;
> }
> @@ -1710,7 +1784,6 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags)
> return ret;
> }
>
> -#ifdef CONFIG_HUGETLB_PAGE
> /*
> * Taking refcount of hugetlb pages needs extra care about race conditions
> * with basic operations like hugepage allocation/free/demotion.
> @@ -1751,7 +1824,7 @@ static int try_memory_failure_hugetlb(unsigned long pfn, int flags, int *hugetlb
> lock_page(head);
>
> if (hwpoison_filter(p)) {
> - ClearPageHWPoison(head);
> + hugetlb_clear_page_hwpoison(head);
> res = -EOPNOTSUPP;
> goto out;
> }
>
