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SubjectRe: [PATCH v2 4/9] mm, hwpoison, hugetlb: support saving mechanism of raw error pages
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On Mon, Jun 27, 2022 at 11:16:06AM +0800, Miaohe Lin wrote:
> On 2022/6/24 7:51, Naoya Horiguchi wrote:
> > From: Naoya Horiguchi <naoya.horiguchi@nec.com>
> >
> > 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@nec.com>
>
> Many thanks for your patch. This patch looks good to me. Some nits below.
>
> >
> <snip>
> >
> > +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 mean to keep additional error info precisely,
>
> It should be s/mean/meaning/ ?

Right, fixed.

>
> > + * so skip to add additional raw error info.
> > + */
> > + if (raw_hwp_unreliable(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;
> > + }
> > +
> > + 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_KERNEL);
> > + if (raw_hwp) {
> > + raw_hwp->page = page;
> > + llist_add(&raw_hwp->node, head);
> > + } else {
> > + /*
> > + * Failed to save raw error info. We no longer trace all
> > + * hwpoisoned subpages, and we need refuse to free/dissolve
> > + * this hwpoisoned hugepage.
> > + */
> > + set_raw_hwp_unreliable(hpage);
> > + return ret;
>
> This "return ret" can be combined into the below one?
>

Right, fixed.

> > + }
> > + return ret;
> > +}
> > +
> > +inline int hugetlb_clear_page_hwpoison(struct page *hpage)
> > +{
> > + struct llist_head *head;
> > + struct llist_node *t, *tnode;
> > +
> > + if (raw_hwp_unreliable(hpage))
> > + return -EBUSY;
>
> Can we try freeing the memory of raw_hwp_list to save possible memory? It seems
> raw_hwp_list becomes unneeded when raw_hwp_unreliable.

Yes, we can. I try to change like that.
Thanks for the suggestion.

- Naoya Horiguchi
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