On Tue, 12 May 2015 09:46:47 +0000 Naoya Horiguchi <[email protected]>
wrote:
> memory_failrue() can run in 2 different mode (specified by MF_COUNT_INCREASED)
> in page refcount perspective. When MF_COUNT_INCREASED is set, memory_failrue()
> assumes that the caller takes a refcount of the target page. And if cleared,
> memory_failure() takes it in it's own.
>
> In current code, however, refcounting is done differently in each caller. For
> example, madvise_hwpoison() uses get_user_pages_fast() and hwpoison_inject()
> uses get_page_unless_zero(). So this inconsistent refcounting causes refcount
> failure especially for thp tail pages. Typical user visible effects are like
> memory leak or VM_BUG_ON_PAGE(!page_count(page)) in isolate_lru_page().
>
> To fix this refcounting issue, this patch introduces get_hwpoison_page() to
> handle thp tail pages in the same manner for each caller of hwpoison code.
>
> There's a non-trivial change around unpoisoning, which now returns immediately
> for thp with "MCE: Memory failure is now running on %#lx\n" message. This is
> not right when split_huge_page() fails. So this patch also allows
> unpoison_memory() to handle thp.
>
> ...
>
> /*
> + * Get refcount for memory error handling:
> + * - @page: raw page
> + */
> +inline int get_hwpoison_page(struct page *page)
> +{
> + struct page *head = compound_head(page);
> +
> + if (PageHuge(head))
> + return get_page_unless_zero(head);
> + else if (PageTransHuge(head))
> + if (get_page_unless_zero(head)) {
> + if (PageTail(page))
> + get_page(page);
> + return 1;
> + } else {
> + return 0;
> + }
> + else
> + return get_page_unless_zero(page);
> +}
This function is a bit weird.
- The comment looks like kerneldoc but isn't kerneldoc
- Why the inline? It isn't fastpath?
- The layout is rather painful. It could be
if (PageHuge(head))
return get_page_unless_zero(head);
if (PageTransHuge(head)) {
if (get_page_unless_zero(head)) {
if (PageTail(page))
get_page(page);
return 1;
} else {
return 0;
}
}
return get_page_unless_zero(page);
- Some illuminating comments would be nice. In particular that code
path where it grabs a ref on the tail page as well as on the head
page. What's going on there?
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