Depending on runtime enablement, this results in a small or large
slowdown, but helps to find certain types of memory corruption.
+ Also, the state of page tracking structures is checked more often as
+ pages are being allocated and freed, as unexpected state changes
+ often happen for same reasons as memory corruption (e.g. double free,
+ use-after-free).
+
For architectures which don't enable ARCH_SUPPORTS_DEBUG_PAGEALLOC,
fill the pages with poison patterns after free_pages() and verify
- the patterns before alloc_pages(). Additionally,
- this option cannot be enabled in combination with hibernation as
- that would result in incorrect warnings of memory corruption after
- a resume because free pages are not saved to the suspend image.
+ the patterns before alloc_pages(). Additionally, this option cannot
+ be enabled in combination with hibernation as that would result in
+ incorrect warnings of memory corruption after a resume because free
+ pages are not saved to the suspend image.
By default this option will have a small overhead, e.g. by not
allowing the kernel mapping to be backed by large pages on some
}
#ifdef CONFIG_DEBUG_VM
-static inline bool free_pcp_prepare(struct page *page)
+/*
+ * With DEBUG_VM enabled, order-0 pages are checked immediately when being freed
+ * to pcp lists. With debug_pagealloc also enabled, they are also rechecked when
+ * moved from pcp lists to free lists.
+ */
+static bool free_pcp_prepare(struct page *page)
{
return free_pages_prepare(page, 0, true);
}
-static inline bool bulkfree_pcp_prepare(struct page *page)
+static bool bulkfree_pcp_prepare(struct page *page)
{
- return false;
+ if (debug_pagealloc_enabled())
+ return free_pages_check(page);
+ else
+ return false;
}
#else
+/*
+ * With DEBUG_VM disabled, order-0 pages being freed are checked only when
+ * moving from pcp lists to free list in order to reduce overhead. With
+ * debug_pagealloc enabled, they are checked also immediately when being freed
+ * to the pcp lists.
+ */
static bool free_pcp_prepare(struct page *page)
{
- return free_pages_prepare(page, 0, false);
+ if (debug_pagealloc_enabled())
+ return free_pages_prepare(page, 0, true);
+ else
+ return free_pages_prepare(page, 0, false);
}
static bool bulkfree_pcp_prepare(struct page *page)
}
#ifdef CONFIG_DEBUG_VM
-static bool check_pcp_refill(struct page *page)
+/*
+ * With DEBUG_VM enabled, order-0 pages are checked for expected state when
+ * being allocated from pcp lists. With debug_pagealloc also enabled, they are
+ * also checked when pcp lists are refilled from the free lists.
+ */
+static inline bool check_pcp_refill(struct page *page)
{
- return false;
+ if (debug_pagealloc_enabled())
+ return check_new_page(page);
+ else
+ return false;
}
-static bool check_new_pcp(struct page *page)
+static inline bool check_new_pcp(struct page *page)
{
return check_new_page(page);
}
#else
-static bool check_pcp_refill(struct page *page)
+/*
+ * With DEBUG_VM disabled, free order-0 pages are checked for expected state
+ * when pcp lists are being refilled from the free lists. With debug_pagealloc
+ * enabled, they are also checked when being allocated from the pcp lists.
+ */
+static inline bool check_pcp_refill(struct page *page)
{
return check_new_page(page);
}
-static bool check_new_pcp(struct page *page)
+static inline bool check_new_pcp(struct page *page)
{
- return false;
+ if (debug_pagealloc_enabled())
+ return check_new_page(page);
+ else
+ return false;
}
#endif /* CONFIG_DEBUG_VM */