[PATCH v3 11/15] mm,hwpoison: Rework soft offline for free pages

nao.horiguchi
2020-06-24T15:02:22Z

From: Oscar Salvador <osalvador@suse.de>

When trying to soft-offline a free page, we need to first take it off
the buddy allocator.
Once we know is out of reach, we can safely flag it as poisoned.

take_page_off_buddy will be used to take a page meant to be poisoned
off the buddy allocator.
take_page_off_buddy calls break_down_buddy_pages, which splits a
higher-order page in case our page belongs to one.

Once the page is under our control, we call page_handle_poison to set it
as poisoned and grab a refcount on it.

Signed-off-by: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
---
ChangeLog v2 -> v3:
- use add_to_free_list() instead of add_to_free_area()
- use del_page_from_free_list() instead of del_page_from_free_area()
- add fast return
- move extern definition to header file as warned by checkpatch.pl
---
include/linux/page-flags.h | 1 +
mm/memory-failure.c | 18 ++++++----
mm/page_alloc.c | 68 ++++++++++++++++++++++++++++++++++++++
3 files changed, 81 insertions(+), 6 deletions(-)

diff --git v5.8-rc1-mmots-2020-06-20-21-44/include/linux/page-flags.h v5.8-rc1-mmots-2020-06-20-21-44_patched/include/linux/page-flags.h
index 6be1aa559b1e..9fa5d4e2d69a 100644
--- v5.8-rc1-mmots-2020-06-20-21-44/include/linux/page-flags.h
+++ v5.8-rc1-mmots-2020-06-20-21-44_patched/include/linux/page-flags.h
@@ -423,6 +423,7 @@ PAGEFLAG(HWPoison, hwpoison, PF_ANY)
TESTSCFLAG(HWPoison, hwpoison, PF_ANY)
#define __PG_HWPOISON (1UL << PG_hwpoison)
extern bool set_hwpoison_free_buddy_page(struct page *page);
+extern bool take_page_off_buddy(struct page *page);
#else
PAGEFLAG_FALSE(HWPoison)
static inline bool set_hwpoison_free_buddy_page(struct page *page)
diff --git v5.8-rc1-mmots-2020-06-20-21-44/mm/memory-failure.c v5.8-rc1-mmots-2020-06-20-21-44_patched/mm/memory-failure.c
index 2e244d5b83e0..d79e756a97be 100644
--- v5.8-rc1-mmots-2020-06-20-21-44/mm/memory-failure.c
+++ v5.8-rc1-mmots-2020-06-20-21-44_patched/mm/memory-failure.c
@@ -78,6 +78,13 @@ EXPORT_SYMBOL_GPL(hwpoison_filter_dev_minor);
EXPORT_SYMBOL_GPL(hwpoison_filter_flags_mask);
EXPORT_SYMBOL_GPL(hwpoison_filter_flags_value);

+static void page_handle_poison(struct page *page)
+{
+ SetPageHWPoison(page);
+ page_ref_inc(page);
+ num_poisoned_pages_inc();
+}
+
static int hwpoison_filter_dev(struct page *p)
{
struct address_space *mapping;
@@ -1876,14 +1883,13 @@ static int soft_offline_in_use_page(struct page *page)

static int soft_offline_free_page(struct page *page)
{
- int rc = dissolve_free_huge_page(page);
+ int rc = -EBUSY;

- if (!rc) {
- if (set_hwpoison_free_buddy_page(page))
- num_poisoned_pages_inc();
- else
- rc = -EBUSY;
+ if (!dissolve_free_huge_page(page) && take_page_off_buddy(page)) {
+ page_handle_poison(page);
+ rc = 0;
}
+
return rc;
}

diff --git v5.8-rc1-mmots-2020-06-20-21-44/mm/page_alloc.c v5.8-rc1-mmots-2020-06-20-21-44_patched/mm/page_alloc.c
index 31c32fe0ecfb..3b145bceb477 100644
--- v5.8-rc1-mmots-2020-06-20-21-44/mm/page_alloc.c
+++ v5.8-rc1-mmots-2020-06-20-21-44_patched/mm/page_alloc.c
@@ -8781,6 +8781,74 @@ bool is_free_buddy_page(struct page *page)
}

#ifdef CONFIG_MEMORY_FAILURE
+/*
+ * Break down a higher-order page in sub-pages, and keep our target out of
+ * buddy allocator.
+ */
+static void break_down_buddy_pages(struct zone *zone, struct page *page,
+ struct page *target, int low, int high,
+ int migratetype)
+{
+ unsigned long size = 1 << high;
+ struct page *current_buddy, *next_page;
+
+ while (high > low) {
+ high--;
+ size >>= 1;
+
+ if (target >= &page[size]) {
+ next_page = page + size;
+ current_buddy = page;
+ } else {
+ next_page = page;
+ current_buddy = page + size;
+ }
+
+ if (set_page_guard(zone, current_buddy, high, migratetype))
+ continue;
+
+ if (current_buddy != target) {
+ add_to_free_list(current_buddy, zone, high, migratetype);
+ set_page_order(current_buddy, high);
+ page = next_page;
+ }
+ }
+}
+
+/*
+ * Take a page that will be marked as poisoned off the buddy allocator.
+ */
+bool take_page_off_buddy(struct page *page)
+{
+ struct zone *zone = page_zone(page);
+ unsigned long pfn = page_to_pfn(page);
+ unsigned long flags;
+ unsigned int order;
+ bool ret = false;
+
+ spin_lock_irqsave(&zone->lock, flags);
+ for (order = 0; order < MAX_ORDER; order++) {
+ struct page *page_head = page - (pfn & ((1 << order) - 1));
+ int buddy_order = page_order(page_head);
+
+ if (PageBuddy(page_head) && buddy_order >= order) {
+ unsigned long pfn_head = page_to_pfn(page_head);
+ int migratetype = get_pfnblock_migratetype(page_head,
+ pfn_head);
+
+ del_page_from_free_list(page_head, zone, buddy_order);
+ break_down_buddy_pages(zone, page_head, page, 0,
+ buddy_order, migratetype);
+ ret = true;
+ break;
+ }
+ if (page_count(page_head) > 0)
+ break;
+ }
+ spin_unlock_irqrestore(&zone->lock, flags);
+ return ret;
+}
+
/*
* Set PG_hwpoison flag if a given page is confirmed to be a free page. This
* test is performed under the zone lock to prevent a race against page
--
2.17.1