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Date: Fri, 14 Dec 2012 11:06:56 +0800
From: Xishi Qiu <qiuxishi@...wei.com>
To: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
CC: Andrew Morton <akpm@...ux-foundation.org>,
Andi Kleen <andi@...stfloor.org>,
Tony Luck <tony.luck@...el.com>,
Wu Fengguang <fengguang.wu@...el.com>,
Jiang Liu <jiang.liu@...wei.com>,
Borislav Petkov <bp@...en8.de>,
Simon Jeons <simon.jeons@...il.com>, <linux-mm@...ck.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: clean up soft_offline_page()
On 2012/12/14 7:01, Naoya Horiguchi wrote:
> Hi,
>
> I wrote this patch inspired by the discussion about fixing mce_bad_pages bug.
> https://lkml.org/lkml/2012/12/7/66
> As mentioned by Andrew, this bug seemed to be undetected because of the
> messiness of soft_offline_page(), so with this patch we can deal with the problem.
>
> Thanks,
> Naoya
> ---
> From: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Date: Thu, 13 Dec 2012 16:08:54 -0500
> Subject: [PATCH] mm: clean up soft_offline_page()
>
> Currently soft_offline_page() is hard to maintain because it has many
> return points and goto statements. All of this mess come from get_any_page().
> This function should only get page refcount as the name implies, but it does
> some page isolating actions like SetPageHWPoison() and dequeuing hugepage.
> This patch corrects it and introduces some internal subroutines to make
> soft offlining code more readable and maintainable.
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> ---
> mm/memory-failure.c | 189 ++++++++++++++++++++++++++++------------------------
> 1 file changed, 101 insertions(+), 88 deletions(-)
>
> diff --git v3.7.orig/mm/memory-failure.c v3.7/mm/memory-failure.c
> index 8b20278..8cef032 100644
> --- v3.7.orig/mm/memory-failure.c
> +++ v3.7/mm/memory-failure.c
> @@ -1368,7 +1368,7 @@ static struct page *new_page(struct page *p, unsigned long private, int **x)
> * that is not free, and 1 for any other page type.
> * For 1 the page is returned with increased page count, otherwise not.
> */
> -static int get_any_page(struct page *p, unsigned long pfn, int flags)
> +static int __get_any_page(struct page *p, unsigned long pfn, int flags)
> {
> int ret;
>
> @@ -1393,11 +1393,9 @@ static int get_any_page(struct page *p, unsigned long pfn, int flags)
> if (!get_page_unless_zero(compound_head(p))) {
> if (PageHuge(p)) {
> pr_info("%s: %#lx free huge page\n", __func__, pfn);
> - ret = dequeue_hwpoisoned_huge_page(compound_head(p));
> + ret = 0;
> } else if (is_free_buddy_page(p)) {
> pr_info("%s: %#lx free buddy page\n", __func__, pfn);
> - /* Set hwpoison bit while page is still isolated */
> - SetPageHWPoison(p);
> ret = 0;
> } else {
> pr_info("%s: %#lx: unknown zero refcount page type %lx\n",
> @@ -1413,23 +1411,45 @@ static int get_any_page(struct page *p, unsigned long pfn, int flags)
> return ret;
> }
>
> +static int get_any_page(struct page *page, unsigned long pfn, int flags)
> +{
> + int ret = __get_any_page(page, pfn, flags);
> +
> + if (ret == 1 && !PageHuge(page) && !PageLRU(page)) {
> + /*
> + * Try to free it.
> + */
> + put_page(page);
> + shake_page(page, 1);
> +
> + /*
> + * Did it turn free?
> + */
> + ret = __get_any_page(page, pfn, 0);
> + if (!PageLRU(page)) {
> + pr_info("soft_offline: %#lx: unknown non LRU page type %lx\n",
> + pfn, page->flags);
> + return -EIO;
> + }
> + }
> + return ret;
> +}
> +
> static int soft_offline_huge_page(struct page *page, int flags)
> {
> int ret;
> unsigned long pfn = page_to_pfn(page);
> struct page *hpage = compound_head(page);
>
> - ret = get_any_page(page, pfn, flags);
> - if (ret < 0)
> - return ret;
> - if (ret == 0)
> - goto done;
> -
> + /* Synchronized using the page lock with memory_failure() */
> + lock_page(hpage);
> if (PageHWPoison(hpage)) {
> + unlock_page(hpage);
> put_page(hpage);
> pr_info("soft offline: %#lx hugepage already poisoned\n", pfn);
> return -EBUSY;
> }
> + unlock_page(hpage);
>
> /* Keep page count to indicate a given hugepage is isolated. */
> ret = migrate_huge_page(hpage, new_page, MPOL_MF_MOVE_ALL, false,
> @@ -1439,85 +1459,19 @@ static int soft_offline_huge_page(struct page *page, int flags)
> pr_info("soft offline: %#lx: migration failed %d, type %lx\n",
> pfn, ret, page->flags);
> return ret;
> + } else {
> + set_page_hwpoison_huge_page(hpage);
> + dequeue_hwpoisoned_huge_page(hpage);
> + atomic_long_add(1<<compound_trans_order(hpage), &mce_bad_pages);
> }
> -done:
> - if (!PageHWPoison(hpage))
> - atomic_long_add(1 << compound_trans_order(hpage),
> - &mce_bad_pages);
> - set_page_hwpoison_huge_page(hpage);
> - dequeue_hwpoisoned_huge_page(hpage);
> /* keep elevated page count for bad page */
> return ret;
> }
>
> -/**
> - * soft_offline_page - Soft offline a page.
> - * @page: page to offline
> - * @flags: flags. Same as memory_failure().
> - *
> - * Returns 0 on success, otherwise negated errno.
> - *
> - * Soft offline a page, by migration or invalidation,
> - * without killing anything. This is for the case when
> - * a page is not corrupted yet (so it's still valid to access),
> - * but has had a number of corrected errors and is better taken
> - * out.
> - *
> - * The actual policy on when to do that is maintained by
> - * user space.
> - *
> - * This should never impact any application or cause data loss,
> - * however it might take some time.
> - *
> - * This is not a 100% solution for all memory, but tries to be
> - * ``good enough'' for the majority of memory.
> - */
> -int soft_offline_page(struct page *page, int flags)
> +int __soft_offline_page(struct page *page, int flags)
> {
> int ret;
> unsigned long pfn = page_to_pfn(page);
> - struct page *hpage = compound_trans_head(page);
> -
> - if (PageHuge(page))
> - return soft_offline_huge_page(page, flags);
> - if (PageTransHuge(hpage)) {
> - if (PageAnon(hpage) && unlikely(split_huge_page(hpage))) {
> - pr_info("soft offline: %#lx: failed to split THP\n",
> - pfn);
> - return -EBUSY;
> - }
> - }
> -
> - ret = get_any_page(page, pfn, flags);
> - if (ret < 0)
> - return ret;
> - if (ret == 0)
> - goto done;
> -
> - /*
> - * Page cache page we can handle?
> - */
> - if (!PageLRU(page)) {
> - /*
> - * Try to free it.
> - */
> - put_page(page);
> - shake_page(page, 1);
> -
> - /*
> - * Did it turn free?
> - */
> - ret = get_any_page(page, pfn, 0);
> - if (ret < 0)
> - return ret;
> - if (ret == 0)
> - goto done;
> - }
> - if (!PageLRU(page)) {
> - pr_info("soft_offline: %#lx: unknown non LRU page type %lx\n",
> - pfn, page->flags);
> - return -EIO;
> - }
>
> lock_page(page);
> wait_on_page_writeback(page);
> @@ -1544,9 +1498,10 @@ int soft_offline_page(struct page *page, int flags)
> */
> if (ret == 1) {
> put_page(page);
> - ret = 0;
> pr_info("soft_offline: %#lx: invalidated\n", pfn);
> - goto done;
> + SetPageHWPoison(page);
> + atomic_long_inc(&mce_bad_pages);
> + return 0;
> }
>
> /*
> @@ -1573,17 +1528,75 @@ int soft_offline_page(struct page *page, int flags)
> pfn, ret, page->flags);
> if (ret > 0)
> ret = -EIO;
> + } else {
> + SetPageHWPoison(page);
> + atomic_long_inc(&mce_bad_pages);
> }
> } else {
> pr_info("soft offline: %#lx: isolation failed: %d, page count %d, type %lx\n",
> pfn, ret, page_count(page), page->flags);
> }
> - if (ret)
> - return ret;
> + return ret;
> +}
> +
> +/**
> + * soft_offline_page - Soft offline a page.
> + * @page: page to offline
> + * @flags: flags. Same as memory_failure().
> + *
> + * Returns 0 on success, otherwise negated errno.
> + *
> + * Soft offline a page, by migration or invalidation,
> + * without killing anything. This is for the case when
> + * a page is not corrupted yet (so it's still valid to access),
> + * but has had a number of corrected errors and is better taken
> + * out.
> + *
> + * The actual policy on when to do that is maintained by
> + * user space.
> + *
> + * This should never impact any application or cause data loss,
> + * however it might take some time.
> + *
> + * This is not a 100% solution for all memory, but tries to be
> + * ``good enough'' for the majority of memory.
> + */
> +int soft_offline_page(struct page *page, int flags)
> +{
> + int ret;
> + unsigned long pfn = page_to_pfn(page);
> + struct page *hpage = compound_trans_head(page);
>
> -done:
> - atomic_long_add(1, &mce_bad_pages);
> - SetPageHWPoison(page);
> + if (PageHWPoison(page)) {
> + pr_info("soft offline: %#lx page already poisoned\n", pfn);
> + return -EBUSY;
> + }
> + if (!PageHuge(page) && PageTransHuge(hpage)) {
> + if (PageAnon(hpage) && unlikely(split_huge_page(hpage))) {
> + pr_info("soft offline: %#lx: failed to split THP\n",
> + pfn);
> + return -EBUSY;
> + }
> + }
> + ret = get_any_page(page, pfn, flags);
> + if (ret < 0)
> + return ret;
> + if (ret) { /* for in-use pages */
> + if (PageHuge(page))
> + soft_offline_huge_page(page, flags);
ret = soft_offline_huge_page(page, flags);
> + else
> + __soft_offline_page(page, flags);
ret = __soft_offline_page(page, flags); right?
Thanks
Xishi Qiu
> + } else { /* for free pages */
> + if (PageHuge(page)) {
> + set_page_hwpoison_huge_page(hpage);
> + dequeue_hwpoisoned_huge_page(hpage);
> + atomic_long_add(1 << compound_trans_order(hpage),
> + &mce_bad_pages);
> + } else {
> + SetPageHWPoison(page);
> + atomic_long_inc(&mce_bad_pages);
> + }
> + }
> /* keep elevated page count for bad page */
> return ret;
> }
--
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