For diagnosing various performance and memory-leak problems, it is helpful
to be able to distinguish pages which are in use as VMalloc pages.
Unfortunately, we cannot use the page_type field in struct page, as
this is in use for mapcount by some drivers which map vmalloced pages
to userspace.
Use a special page->mapping value to distinguish VMalloc pages from
other kinds of pages. Also record a pointer to the vm_struct and the
offset within the area in struct page to help reconstruct exactly what
this page is being used for.
Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
---
v7: Use a value which has the bottom bit set so that page_mapping()
returns NULL. Comments updated to note this bit of "cleverness".
fs/proc/page.c | 2 ++
include/linux/mm_types.h | 5 +++++
include/linux/page-flags.h | 26 ++++++++++++++++++++++++++
include/uapi/linux/kernel-page-flags.h | 1 +
mm/vmalloc.c | 5 ++++-
tools/vm/page-types.c | 1 +
6 files changed, 39 insertions(+), 1 deletion(-)
diff --git a/fs/proc/page.c b/fs/proc/page.c
index 792c78a49174..fc83dae1af7b 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -156,6 +156,8 @@ u64 stable_page_flags(struct page *page)
u |= 1 << KPF_BALLOON;
if (PageTable(page))
u |= 1 << KPF_PGTABLE;
+ if (PageVMalloc(page))
+ u |= 1 << KPF_VMALLOC;
if (page_is_idle(page))
u |= 1 << KPF_IDLE;
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 21e1b6a9f113..8a4698b368de 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -153,6 +153,11 @@ struct page {
spinlock_t ptl;
#endif
};
+ struct { /* VMalloc pages */
+ struct vm_struct *vm_area;
+ unsigned long vm_offset;
+ unsigned long _vm_id; /* MAPPING_VMalloc */
+ };
struct { /* ZONE_DEVICE pages */
/** @pgmap: Points to the hosting device page map. */
struct dev_pagemap *pgmap;
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 901943e4754b..588b8dd28a85 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -699,6 +699,32 @@ PAGE_TYPE_OPS(Kmemcg, kmemcg)
*/
PAGE_TYPE_OPS(Table, table)
+/*
+ * vmalloc pages may be mapped to userspace, so we need some other way
+ * to distinguish them from other kinds of pages. Use page->mapping for
+ * this purpose. Values below 0x1000 cannot be real pointers. Setting
+ * the bottom bit makes page_mapping() return NULL, which is what we want.
+ */
+#define MAPPING_VMalloc (void *)0x441
+
+#define PAGE_MAPPING_OPS(name) \
+static __always_inline int Page##name(struct page *page) \
+{ \
+ return page->mapping == MAPPING_##name; \
+} \
+static __always_inline void __SetPage##name(struct page *page) \
+{ \
+ VM_BUG_ON_PAGE(page->mapping != NULL, page); \
+ page->mapping = MAPPING_##name; \
+} \
+static __always_inline void __ClearPage##name(struct page *page) \
+{ \
+ VM_BUG_ON_PAGE(page->mapping != MAPPING_##name, page); \
+ page->mapping = NULL; \
+}
+
+PAGE_MAPPING_OPS(VMalloc)
+
extern bool is_free_buddy_page(struct page *page);
__PAGEFLAG(Isolated, isolated, PF_ANY);
diff --git a/include/uapi/linux/kernel-page-flags.h b/include/uapi/linux/kernel-page-flags.h
index 21b9113c69da..6800968b8f47 100644
--- a/include/uapi/linux/kernel-page-flags.h
+++ b/include/uapi/linux/kernel-page-flags.h
@@ -36,5 +36,6 @@
#define KPF_ZERO_PAGE 24
#define KPF_IDLE 25
#define KPF_PGTABLE 26
+#define KPF_VMALLOC 27
#endif /* _UAPILINUX_KERNEL_PAGE_FLAGS_H */
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 1863390fa09c..99331453e114 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1522,7 +1522,7 @@ static void __vunmap(const void *addr, int deallocate_pages)
for (i = 0; i < area->nr_pages; i++) {
struct page *page = area->pages[i];
- BUG_ON(!page);
+ __ClearPageVMalloc(page);
__free_pages(page, 0);
}
@@ -1691,6 +1691,9 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
area->nr_pages = i;
goto fail;
}
+ __SetPageVMalloc(page);
+ page->vm_area = area;
+ page->vm_offset = i;
area->pages[i] = page;
if (gfpflags_allow_blocking(gfp_mask))
cond_resched();
diff --git a/tools/vm/page-types.c b/tools/vm/page-types.c
index cce853dca691..25cc21855be4 100644
--- a/tools/vm/page-types.c
+++ b/tools/vm/page-types.c
@@ -132,6 +132,7 @@ static const char * const page_flag_names[] = {
[KPF_THP] = "t:thp",
[KPF_BALLOON] = "o:balloon",
[KPF_PGTABLE] = "g:pgtable",
+ [KPF_VMALLOC] = "V:vmalloc",
[KPF_ZERO_PAGE] = "z:zero_page",
[KPF_IDLE] = "i:idle_page",
--
2.18.0
