On 2022/7/7 7:06, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Wed, Jul 06, 2022 at 10:37:50AM +0800, Miaohe Lin wrote:
>> On 2022/7/4 9:33, 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>
>>> ---
> ...
>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>>> index 66bb39e0fce8..ccd470f0194c 100644
>>> --- a/mm/hugetlb.c
>>> +++ b/mm/hugetlb.c
>>> @@ -1535,17 +1535,15 @@ static void __update_and_free_page(struct hstate *h, struct page *page)
>>> if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
>>> return;
>>>
>>> - if (hugetlb_vmemmap_restore(h, page)) {
>>> - spin_lock_irq(&hugetlb_lock);
>>> - /*
>>> - * If we cannot allocate vmemmap pages, just refuse to free the
>>> - * page and put the page back on the hugetlb free list and treat
>>> - * as a surplus page.
>>> - */
>>> - add_hugetlb_page(h, page, true);
>>> - spin_unlock_irq(&hugetlb_lock);
>>> - return;
>>> - }
>>> + if (hugetlb_vmemmap_restore(h, page))
>>> + goto fail;
>>> +
>>> + /*
>>> + * 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)))
>>> + goto fail;
>>
>> IIUC, HPageVmemmapOptimized must have been cleared via hugetlb_vmemmap_restore above. So
>> VM_BUG_ON_PAGE(!HPageVmemmapOptimized(page), page) in add_hugetlb_page will be triggered
>> if we go to fail here. add_hugetlb_page is expected to be called when we cannot allocate
>> vmemmap pages.
>
> Thanks a lot, you're right. I shouldn't simply factor the failure path with
> the goto label. I think that it's hard to undo hugetlb_vmemmap_restore(), so
> checking HPageRawHwpUnreliable() before hugetlb_vmemmap_restore(), then
> try to hugetlb_clear_page_hwpoison() after it (where tail pages are available).
Sounds feasible.
>
>>
>>>
>>> for (i = 0; i < pages_per_huge_page(h);
>>> i++, subpage = mem_map_next(subpage, page, i)) {
>>> @@ -1566,6 +1564,16 @@ static void __update_and_free_page(struct hstate *h, struct page *page)
>>> } else {
>>> __free_pages(page, huge_page_order(h));
>>> }
>>> + return;
>>> +fail:
>>> + spin_lock_irq(&hugetlb_lock);
>>> + /*
>>> + * If we cannot allocate vmemmap pages or cannot identify raw hwpoison
>>> + * subpages reliably, just refuse to free the page and put the page
>>> + * back on the hugetlb free list and treat as a surplus page.
>>> + */
>>> + add_hugetlb_page(h, page, true);
>>> + spin_unlock_irq(&hugetlb_lock);
>>> }
>>>
>>> /*
>>> @@ -2109,15 +2117,6 @@ 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..53bf7486a245 100644
>>> --- a/mm/memory-failure.c
>>> +++ b/mm/memory-failure.c
>>> @@ -1664,6 +1664,82 @@ int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
>>> EXPORT_SYMBOL_GPL(mf_dax_kill_procs);
>>> #endif /* CONFIG_FS_DAX */
>>>
>>> +/*
>>> + * 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 inline 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;
>>> +
>>> + /*
>>> + * 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;
>>
>> If we return here, num_poisoned_pages can't reflect the all hwpoisoned hugepages?
>
> No, it can't now. Currently we try to (and fail) count only the number
> hwpoison subpages with raw_hwp_info. If we want to track all corrupted
> pages (including hwpoison subpages without raw_hwp_info), maybe running the
> following part first in this function could make it better.
>
> ret = TestSetPageHWPoison(hpage) ? -EHWPOISON : 0;
> /* the first error event will be counted in action_result(). */
> if (ret)
> num_poisoned_pages_inc();
>
> But I like the option you suggest below.
>
>>
>>> + 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;
>>> + }
>>> +
>>> + ret = TestSetPageHWPoison(hpage) ? -EHWPOISON : 0;
>>> + /* the first error event will be counted in action_result(). */
>>> + if (ret)
>>> + num_poisoned_pages_inc();
>>> +
>>> + raw_hwp = kmalloc(sizeof(struct raw_hwp_page), GFP_ATOMIC);
>>> + if (raw_hwp) {
>>> + raw_hwp->page = page;
>>> + llist_add(&raw_hwp->node, head);
>>
>> IMHO, we might need to do num_poisoned_pages_inc here because we decrement the
>> num_poisoned_pages according to the llist length.
>
> Yes, if we'd like to count only hwpoisoned subpages with raw_hwp_info,
> doing num_poisoned_pages_inc here is fine.
>
>>> + } 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;
>>> +}
>>> +
>>> +inline int hugetlb_clear_page_hwpoison(struct page *hpage)
>>
>> off-the-topic: Is "inline" needed here? I see hugetlb_clear_page_hwpoison is "extern" above.
>
> Maybe not, this code is not performance-sensitive and actually this inline
> is a leftover of updates in the previous versions. I'll remove this.
>
>>
>>> +{
>>> + 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);
>>
>> IMHO, in HPageRawHwpUnreliable(hpage) case, it's better not to do SetPageHWPoison here.
>> Because hugepage won't be dissolved and thus we cannot write any data to some tail struct
>> pages if HugeTLB Vmemmap Optimization is enabled. Freeing the memory here should be enough.
>
> This is a good point, too. Current version surely does not work with HVO, so
> I think of simply giving up clearing hwpoison when HPageVmemmapOptimized is
> true. And I should leave some inline comment about this.
Sounds like a good idea. This will make the life easier.
>
>>> + kfree(p);
>>> + }
>>> + llist_del_all(head);
>>> + return 0;
>>> +}
>>
>> I thought num_poisoned_pages_dec is missing and return value is unneeded. But this is changed
>> in next patch. So it should be fine here.
>
> OK.
>
>>
>>> +
>>> /*
>>> * Called from hugetlb code with hugetlb_lock held.
>>> *
>>> @@ -1698,7 +1774,7 @@ 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;
>>> }
>>> @@ -1751,7 +1827,7 @@ 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;
>>> }
>>>
>>
>> Many thanks for your hard work. :)
>
> Thanks for the detailed review and feedback.
>
> - Naoya Horiguchi
Thanks.
>
