mm/vmalloc.c: improve readability and rewrite vmap_area

PATCH Superseded Pengfei Li 2 participants 5 messages Jul 16, 2019

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Memory management vmalloc

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Pengfei Li

author

2019-07-16 13:26 UTC #0 lore raw

v5 cover mm/vmalloc.c: improve readability and rewrite vmap_area

v4 -> v5
* Base on next-20190716
* patch 1: From Uladzislau Rezki (Sony) <[email protected]> (author)
- https://lkml.org/lkml/2019/7/16/276
* patch 2: Use v3

v3 -> v4:
* Base on next-20190711
* patch 1: From: Uladzislau Rezki (Sony) <[email protected]> (author)
- https://lkml.org/lkml/2019/7/3/661
* patch 2: Modify the layout of struct vmap_area for readability

v2 -> v3:
* patch 1-4: Abandoned
* patch 5:
- Eliminate "flags" (suggested by Uladzislau Rezki)
- Base on https://lkml.org/lkml/2019/6/6/455

    and https://lkml.org/lkml/2019/7/3/661

v1 -> v2:
* patch 3: Rename __find_vmap_area to __search_va_in_busy_tree instead of __search_va_from_busy_tree.
* patch 5: Add motivation and necessary test data to the commit message.
* patch 5: Let va->flags use only some low bits of va_start instead of completely overwriting va_start.

The current implementation of struct vmap_area wasted space.

After applying this commit, sizeof(struct vmap_area) has been reduced from 11 words to 8 words.

Pengfei Li (1):
mm/vmalloc: modify struct vmap_area to reduce its size

Uladzislau Rezki (Sony) (1):
mm/vmalloc: do not keep unpurged areas in the busy tree

 include/linux/vmalloc.h | 20 +++++++----
 mm/vmalloc.c            | 76 +++++++++++++++++++++++++++++------------
 2 files changed, 67 insertions(+), 29 deletions(-)

Signature · 1 line

2.21.0

Pengfei Li

author

2019-07-16 13:26 UTC #1 lore raw

PATCH v5 1/2 mm/vmalloc: do not keep unpurged areas in the busy tree

From: "Uladzislau Rezki (Sony)" <[email protected]>

The busy tree can be quite big, even though the area is freed or unmapped it still stays there until "purge" logic removes it.

1) Optimize and reduce the size of "busy" tree by removing a node from it right away as soon as user triggers free paths. It is possible to do so, because the allocation is done using another augmented tree.

The vmalloc test driver shows the difference, for example the "fix_size_alloc_test" is ~11% better comparing with default configuration:

sudo ./test_vmalloc.sh performance

<default>
Summary: fix_size_alloc_test loops: 1000000 avg: 993985 usec
Summary: full_fit_alloc_test loops: 1000000 avg: 973554 usec
Summary: long_busy_list_alloc_test loops: 1000000 avg: 12617652 usec <default>

<this patch>
Summary: fix_size_alloc_test loops: 1000000 avg: 882263 usec
Summary: full_fit_alloc_test loops: 1000000 avg: 973407 usec
Summary: long_busy_list_alloc_test loops: 1000000 avg: 12593929 usec <this patch>

2) Since the busy tree now contains allocated areas only and does not interfere with lazily free nodes, introduce the new function show_purge_info() that dumps "unpurged" areas that is propagated through "/proc/vmallocinfo".

3) Eliminate VM_LAZY_FREE flag.

Signed-off-by Uladzislau Rezki (Sony) <[email protected]>

---
 mm/vmalloc.c | 52 ++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 44 insertions(+), 8 deletions(-)

mm/vmalloc.c +44 -8

index 4fa8d84599b0..71d8040a8a0b 100644
@@ -329,7 +329,6 @@ EXPORT_SYMBOL(vmalloc_to_pfn);
 #define DEBUG_AUGMENT_PROPAGATE_CHECK 0
 #define DEBUG_AUGMENT_LOWEST_MATCH_CHECK 0
 
-#define VM_LAZY_FREE	0x02
 #define VM_VM_AREA	0x04
 
 static DEFINE_SPINLOCK(vmap_area_lock);

@@ -1276,7 +1275,14 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end)
 	llist_for_each_entry_safe(va, n_va, valist, purge_list) {
 		unsigned long nr = (va->va_end - va->va_start) >> PAGE_SHIFT;
 
-		__free_vmap_area(va);
+		/*
+		 * Finally insert or merge lazily-freed area. It is
+		 * detached and there is no need to "unlink" it from
+		 * anything.
+		 */
+		merge_or_add_vmap_area(va,
+			&free_vmap_area_root, &free_vmap_area_list);
+
 		atomic_long_sub(nr, &vmap_lazy_nr);
 
 		if (atomic_long_read(&vmap_lazy_nr) < resched_threshold)

@@ -1318,6 +1324,10 @@ static void free_vmap_area_noflush(struct vmap_area *va)
 {
 	unsigned long nr_lazy;
 
+	spin_lock(&vmap_area_lock);
+	unlink_va(va, &vmap_area_root);
+	spin_unlock(&vmap_area_lock);
+
 	nr_lazy = atomic_long_add_return((va->va_end - va->va_start) >>
 				PAGE_SHIFT, &vmap_lazy_nr);

@@ -2137,14 +2147,13 @@ struct vm_struct *remove_vm_area(const void *addr)
 
 	might_sleep();
 
-	va = find_vmap_area((unsigned long)addr);
+	spin_lock(&vmap_area_lock);
+	va = __find_vmap_area((unsigned long)addr);
 	if (va && va->flags & VM_VM_AREA) {
 		struct vm_struct *vm = va->vm;
 
-		spin_lock(&vmap_area_lock);
 		va->vm = NULL;
 		va->flags &= ~VM_VM_AREA;
-		va->flags |= VM_LAZY_FREE;
 		spin_unlock(&vmap_area_lock);
 
 		kasan_free_shadow(vm);

@@ -2152,6 +2161,8 @@ struct vm_struct *remove_vm_area(const void *addr)
 
 		return vm;
 	}
+
+	spin_unlock(&vmap_area_lock);
 	return NULL;
 }

@@ -3431,6 +3442,22 @@ static void show_numa_info(struct seq_file *m, struct vm_struct *v)
 	}
 }
 
+static void show_purge_info(struct seq_file *m)
+{
+	struct llist_node *head;
+	struct vmap_area *va;
+
+	head = READ_ONCE(vmap_purge_list.first);
+	if (head == NULL)
+		return;
+
+	llist_for_each_entry(va, head, purge_list) {
+		seq_printf(m, "0x%pK-0x%pK %7ld unpurged vm_area\n",
+			(void *)va->va_start, (void *)va->va_end,
+			va->va_end - va->va_start);
+	}
+}
+
 static int s_show(struct seq_file *m, void *p)
 {
 	struct vmap_area *va;

@@ -3443,10 +3470,9 @@ static int s_show(struct seq_file *m, void *p)
 	 * behalf of vmap area is being tear down or vm_map_ram allocation.
 	 */
 	if (!(va->flags & VM_VM_AREA)) {
-		seq_printf(m, "0x%pK-0x%pK %7ld %s\n",
+		seq_printf(m, "0x%pK-0x%pK %7ld vm_map_ram\n",
 			(void *)va->va_start, (void *)va->va_end,
-			va->va_end - va->va_start,
-			va->flags & VM_LAZY_FREE ? "unpurged vm_area" : "vm_map_ram");
+			va->va_end - va->va_start);
 
 		return 0;
 	}

@@ -3482,6 +3508,16 @@ static int s_show(struct seq_file *m, void *p)
 
 	show_numa_info(m, v);
 	seq_putc(m, '\n');
+
+	/*
+	 * As a final step, dump "unpurged" areas. Note,
+	 * that entire "/proc/vmallocinfo" output will not
+	 * be address sorted, because the purge list is not
+	 * sorted.
+	 */
+	if (list_is_last(&va->list, &vmap_area_list))
+		show_purge_info(m);
+
 	return 0;
 }

Signature · 1 line

2.21.0

Pengfei Li

author

2019-07-16 13:26 UTC #2 lore raw

PATCH v5 2/2 mm/vmalloc: modify struct vmap_area to reduce its size

In reply to Pengfei Li

Objective
---------
The current implementation of struct vmap_area wasted space.

After applying this commit, sizeof(struct vmap_area) has been reduced from 11 words to 8 words.

Description
-----------
1) Pack "subtree_max_size", "vm" and "purge_list". This is no problem because
A) "subtree_max_size" is only used when vmap_area is in "free" tree
B) "vm" is only used when vmap_area is in "busy" tree
C) "purge_list" is only used when vmap_area is in vmap_purge_list

2) Eliminate "flags".
Since only one flag VM_VM_AREA is being used, and the same thing can be done by judging whether "vm" is NULL, then the "flags" can be eliminated.

Signed-off-by Pengfei Li <[email protected]>

---
 include/linux/vmalloc.h | 20 +++++++++++++-------
 mm/vmalloc.c            | 24 ++++++++++--------------
 2 files changed, 23 insertions(+), 21 deletions(-)

include/linux/vmalloc.h +13 -7

index 9b21d0047710..a1334bd18ef1 100644
@@ -51,15 +51,21 @@ struct vmap_area {
 	unsigned long va_start;
 	unsigned long va_end;
 
-	/*
-	 * Largest available free size in subtree.
-	 */
-	unsigned long subtree_max_size;
-	unsigned long flags;
 	struct rb_node rb_node;         /* address sorted rbtree */
 	struct list_head list;          /* address sorted list */
-	struct llist_node purge_list;    /* "lazy purge" list */
-	struct vm_struct *vm;
+
+	/*
+	 * The following three variables can be packed, because
+	 * a vmap_area object is always one of the three states:
+	 *    1) in "free" tree (root is vmap_area_root)
+	 *    2) in "busy" tree (root is free_vmap_area_root)
+	 *    3) in purge list  (head is vmap_purge_list)
+	 */
+	union {
+		unsigned long subtree_max_size; /* in "free" tree */
+		struct vm_struct *vm;           /* in "busy" tree */
+		struct llist_node purge_list;   /* in purge list */
+	};
 };
 
 /*

mm/vmalloc.c +10 ~~-14~~

index 71d8040a8a0b..39bf9cf4175a 100644
@@ -329,7 +329,6 @@ EXPORT_SYMBOL(vmalloc_to_pfn);
 #define DEBUG_AUGMENT_PROPAGATE_CHECK 0
 #define DEBUG_AUGMENT_LOWEST_MATCH_CHECK 0
 
-#define VM_VM_AREA	0x04
 
 static DEFINE_SPINLOCK(vmap_area_lock);
 /* Export for kexec only */

@@ -1115,7 +1114,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
 
 	va->va_start = addr;
 	va->va_end = addr + size;
-	va->flags = 0;
+	va->vm = NULL;
 	insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
 
 	spin_unlock(&vmap_area_lock);

@@ -1922,7 +1921,6 @@ void __init vmalloc_init(void)
 		if (WARN_ON_ONCE(!va))
 			continue;
 
-		va->flags = VM_VM_AREA;
 		va->va_start = (unsigned long)tmp->addr;
 		va->va_end = va->va_start + tmp->size;
 		va->vm = tmp;

@@ -2020,7 +2018,6 @@ static void setup_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
 	vm->size = va->va_end - va->va_start;
 	vm->caller = caller;
 	va->vm = vm;
-	va->flags |= VM_VM_AREA;
 	spin_unlock(&vmap_area_lock);
 }

@@ -2125,10 +2122,10 @@ struct vm_struct *find_vm_area(const void *addr)
 	struct vmap_area *va;
 
 	va = find_vmap_area((unsigned long)addr);
-	if (va && va->flags & VM_VM_AREA)
-		return va->vm;
+	if (!va)
+		return NULL;
 
-	return NULL;
+	return va->vm;
 }
 
 /**

@@ -2149,11 +2146,10 @@ struct vm_struct *remove_vm_area(const void *addr)
 
 	spin_lock(&vmap_area_lock);
 	va = __find_vmap_area((unsigned long)addr);
-	if (va && va->flags & VM_VM_AREA) {
+	if (va && va->vm) {
 		struct vm_struct *vm = va->vm;
 
 		va->vm = NULL;
-		va->flags &= ~VM_VM_AREA;
 		spin_unlock(&vmap_area_lock);
 
 		kasan_free_shadow(vm);

@@ -2856,7 +2852,7 @@ long vread(char *buf, char *addr, unsigned long count)
 		if (!count)
 			break;
 
-		if (!(va->flags & VM_VM_AREA))
+		if (!va->vm)
 			continue;
 
 		vm = va->vm;

@@ -2936,7 +2932,7 @@ long vwrite(char *buf, char *addr, unsigned long count)
 		if (!count)
 			break;
 
-		if (!(va->flags & VM_VM_AREA))
+		if (!va->vm)
 			continue;
 
 		vm = va->vm;

@@ -3466,10 +3462,10 @@ static int s_show(struct seq_file *m, void *p)
 	va = list_entry(p, struct vmap_area, list);
 
 	/*
-	 * s_show can encounter race with remove_vm_area, !VM_VM_AREA on
-	 * behalf of vmap area is being tear down or vm_map_ram allocation.
+	 * If !va->vm then this vmap_area object is allocated
+	 * by vm_map_ram.
 	 */
-	if (!(va->flags & VM_VM_AREA)) {
+	if (!va->vm) {
 		seq_printf(m, "0x%pK-0x%pK %7ld vm_map_ram\n",
 			(void *)va->va_start, (void *)va->va_end,
 			va->va_end - va->va_start);

Signature · 1 line

2.21.0

Uladzislau Rezki

maintainer

2019-07-16 14:35 UTC #3 lore raw

Re: [PATCH v5 2/2] mm/vmalloc: modify struct vmap_area to reduce its size

Quoted 145 lines · Pengfei Li

Objective
---------
The current implementation of struct vmap_area wasted space.

After applying this commit, sizeof(struct vmap_area) has been reduced from 11 words to 8 words.

2) Eliminate "flags".
Since only one flag VM_VM_AREA is being used, and the same thing can be done by judging whether "vm" is NULL, then the "flags" can be eliminated.

Signed-off-by Pengfei Li <[email protected]>

---
 include/linux/vmalloc.h | 20 +++++++++++++-------
 mm/vmalloc.c            | 24 ++++++++++--------------
 2 files changed, 23 insertions(+), 21 deletions(-)

include/linux/vmalloc.h +13 -7

index 9b21d0047710..a1334bd18ef1 100644
@@ -51,15 +51,21 @@ struct vmap_area {
 	unsigned long va_start;
 	unsigned long va_end;
 
-	/*
-	 * Largest available free size in subtree.
-	 */
-	unsigned long subtree_max_size;
-	unsigned long flags;
 	struct rb_node rb_node;         /* address sorted rbtree */
 	struct list_head list;          /* address sorted list */
-	struct llist_node purge_list;    /* "lazy purge" list */
-	struct vm_struct *vm;
+
+	/*
+	 * The following three variables can be packed, because
+	 * a vmap_area object is always one of the three states:
+	 *    1) in "free" tree (root is vmap_area_root)
+	 *    2) in "busy" tree (root is free_vmap_area_root)
+	 *    3) in purge list  (head is vmap_purge_list)
+	 */
+	union {
+		unsigned long subtree_max_size; /* in "free" tree */
+		struct vm_struct *vm;           /* in "busy" tree */
+		struct llist_node purge_list;   /* in purge list */
+	};
 };
 
 /*

mm/vmalloc.c +7 ~~-11~~

index 71d8040a8a0b..39bf9cf4175a 100644
@@ -329,7 +329,6 @@ EXPORT_SYMBOL(vmalloc_to_pfn);
 #define DEBUG_AUGMENT_PROPAGATE_CHECK 0
 #define DEBUG_AUGMENT_LOWEST_MATCH_CHECK 0
 
-#define VM_VM_AREA	0x04
 
 static DEFINE_SPINLOCK(vmap_area_lock);
 /* Export for kexec only */

@@ -1115,7 +1114,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
 
 	va->va_start = addr;
 	va->va_end = addr + size;
-	va->flags = 0;
+	va->vm = NULL;
 	insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
 
 	spin_unlock(&vmap_area_lock);

@@ -1922,7 +1921,6 @@ void __init vmalloc_init(void)
 		if (WARN_ON_ONCE(!va))
 			continue;
 
-		va->flags = VM_VM_AREA;
 		va->va_start = (unsigned long)tmp->addr;
 		va->va_end = va->va_start + tmp->size;
 		va->vm = tmp;

@@ -2020,7 +2018,6 @@ static void setup_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
 	vm->size = va->va_end - va->va_start;
 	vm->caller = caller;
 	va->vm = vm;
-	va->flags |= VM_VM_AREA;
 	spin_unlock(&vmap_area_lock);
 }

@@ -2125,10 +2122,10 @@ struct vm_struct *find_vm_area(const void *addr)
 	struct vmap_area *va;
 
 	va = find_vmap_area((unsigned long)addr);
-	if (va && va->flags & VM_VM_AREA)
-		return va->vm;
+	if (!va)
+		return NULL;
 
-	return NULL;
+	return va->vm;
 }
 
 /**

@@ -2149,11 +2146,10 @@ struct vm_struct *remove_vm_area(const void *addr)
 
 	spin_lock(&vmap_area_lock);
 	va = __find_vmap_area((unsigned long)addr);
-	if (va && va->flags & VM_VM_AREA) {
+	if (va && va->vm) {
 		struct vm_struct *vm = va->vm;
 
 		va->vm = NULL;
-		va->flags &= ~VM_VM_AREA;
 		spin_unlock(&vmap_area_lock);
 
 		kasan_free_shadow(vm);

@@ -2856,7 +2852,7 @@ long vread(char *buf, char *addr, unsigned long count)
 		if (!count)
 			break;
 
-		if (!(va->flags & VM_VM_AREA))
+		if (!va->vm)
 			continue;
 
 		vm = va->vm;

@@ -2936,7 +2932,7 @@ long vwrite(char *buf, char *addr, unsigned long count)
 		if (!count)
 			break;
 
-		if (!(va->flags & VM_VM_AREA))
+		if (!va->vm)
 			continue;
 
 		vm = va->vm;

mm/vmalloc.c static int s_show(struct seq_file *m, void *p) · line 3467

Quoted 8 lines

mm/vmalloc.c +2 -2

@@ -3466,10 +3462,10 @@ static int s_show(struct seq_file *m, void *p)
 	va = list_entry(p, struct vmap_area, list);
 
 	/*
-	 * s_show can encounter race with remove_vm_area, !VM_VM_AREA on
-	 * behalf of vmap area is being tear down or vm_map_ram allocation.
+	 * If !va->vm then this vmap_area object is allocated
+	 * by vm_map_ram.
 	 */

This point is still valid. There is a race between remove_vm_area() vs s_show() and va->vm = NULL. So, please keep that comment.

Quoted 8 lines

mm/vmalloc.c +1 -1

-	if (!(va->flags & VM_VM_AREA)) {
+	if (!va->vm) {
 		seq_printf(m, "0x%pK-0x%pK %7ld vm_map_ram\n",
 			(void *)va->va_start, (void *)va->va_end,
 			va->va_end - va->va_start);

Signature · 1 line

2.21.0

--
Vlad Rezki

Pengfei Li

author

2019-07-16 15:07 UTC #4 lore raw

Re: [PATCH v5 2/2] mm/vmalloc: modify struct vmap_area to reduce its size

Quoted 149 lines · Uladzislau Rezki

Quoted 147 lines · Pengfei Li

Objective
---------
The current implementation of struct vmap_area wasted space.

After applying this commit, sizeof(struct vmap_area) has been reduced from 11 words to 8 words.

2) Eliminate "flags".
Since only one flag VM_VM_AREA is being used, and the same thing can be done by judging whether "vm" is NULL, then the "flags" can be eliminated.

Signed-off-by Pengfei Li <[email protected]>

---
 include/linux/vmalloc.h | 20 +++++++++++++-------
 mm/vmalloc.c            | 24 ++++++++++--------------
 2 files changed, 23 insertions(+), 21 deletions(-)

include/linux/vmalloc.h +13 -7

index 9b21d0047710..a1334bd18ef1 100644
@@ -51,15 +51,21 @@ struct vmap_area {
      unsigned long va_start;
      unsigned long va_end;
 
-     /*
-      * Largest available free size in subtree.
-      */
-     unsigned long subtree_max_size;
-     unsigned long flags;
      struct rb_node rb_node;         /* address sorted rbtree */
      struct list_head list;          /* address sorted list */
-     struct llist_node purge_list;    /* "lazy purge" list */
-     struct vm_struct *vm;
+
+     /*
+      * The following three variables can be packed, because
+      * a vmap_area object is always one of the three states:
+      *    1) in "free" tree (root is vmap_area_root)
+      *    2) in "busy" tree (root is free_vmap_area_root)
+      *    3) in purge list  (head is vmap_purge_list)
+      */
+     union {
+             unsigned long subtree_max_size; /* in "free" tree */
+             struct vm_struct *vm;           /* in "busy" tree */
+             struct llist_node purge_list;   /* in purge list */
+     };
 };
 
 /*

mm/vmalloc.c +7 ~~-11~~

index 71d8040a8a0b..39bf9cf4175a 100644
@@ -329,7 +329,6 @@ EXPORT_SYMBOL(vmalloc_to_pfn);
 #define DEBUG_AUGMENT_PROPAGATE_CHECK 0
 #define DEBUG_AUGMENT_LOWEST_MATCH_CHECK 0
 
-#define VM_VM_AREA   0x04
 
 static DEFINE_SPINLOCK(vmap_area_lock);
 /* Export for kexec only */

@@ -1115,7 +1114,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
 
      va->va_start = addr;
      va->va_end = addr + size;
-     va->flags = 0;
+     va->vm = NULL;
      insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
 
      spin_unlock(&vmap_area_lock);

@@ -1922,7 +1921,6 @@ void __init vmalloc_init(void)
              if (WARN_ON_ONCE(!va))
                      continue;
 
-             va->flags = VM_VM_AREA;
              va->va_start = (unsigned long)tmp->addr;
              va->va_end = va->va_start + tmp->size;
              va->vm = tmp;

@@ -2020,7 +2018,6 @@ static void setup_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
      vm->size = va->va_end - va->va_start;
      vm->caller = caller;
      va->vm = vm;
-     va->flags |= VM_VM_AREA;
      spin_unlock(&vmap_area_lock);
 }

@@ -2125,10 +2122,10 @@ struct vm_struct *find_vm_area(const void *addr)
      struct vmap_area *va;
 
      va = find_vmap_area((unsigned long)addr);
-     if (va && va->flags & VM_VM_AREA)
-             return va->vm;
+     if (!va)
+             return NULL;
 
-     return NULL;
+     return va->vm;
 }
 
 /**

@@ -2149,11 +2146,10 @@ struct vm_struct *remove_vm_area(const void *addr)
 
      spin_lock(&vmap_area_lock);
      va = __find_vmap_area((unsigned long)addr);
-     if (va && va->flags & VM_VM_AREA) {
+     if (va && va->vm) {
              struct vm_struct *vm = va->vm;
 
              va->vm = NULL;
-             va->flags &= ~VM_VM_AREA;
              spin_unlock(&vmap_area_lock);
 
              kasan_free_shadow(vm);

@@ -2856,7 +2852,7 @@ long vread(char *buf, char *addr, unsigned long count)
              if (!count)
                      break;
 
-             if (!(va->flags & VM_VM_AREA))
+             if (!va->vm)
                      continue;
 
              vm = va->vm;

@@ -2936,7 +2932,7 @@ long vwrite(char *buf, char *addr, unsigned long count)
              if (!count)
                      break;
 
-             if (!(va->flags & VM_VM_AREA))
+             if (!va->vm)
                      continue;
 
              vm = va->vm;

@@ -3466,10 +3462,10 @@ static int s_show(struct seq_file *m, void *p)
      va = list_entry(p, struct vmap_area, list);

Quoted 9 lines

mm/vmalloc.c static int s_show(struct seq_file *m, void *p) · line 3467
Quoted 6 lines
mm/vmalloc.c +2 -2
      /*
-      * s_show can encounter race with remove_vm_area, !VM_VM_AREA on
-      * behalf of vmap area is being tear down or vm_map_ram allocation.
+      * If !va->vm then this vmap_area object is allocated
+      * by vm_map_ram.
       */
This point is still valid. There is a race between remove_vm_area() vs s_show() and va->vm = NULL. So, please keep that comment.

Thank you.
I will keep the comment in the next version.

Quoted 11 lines

Quoted 8 lines

mm/vmalloc.c +1 -2

-     if (!(va->flags & VM_VM_AREA)) {
+     if (!va->vm) {
              seq_printf(m, "0x%pK-0x%pK %7ld vm_map_ram\n",
                      (void *)va->va_start, (void *)va->va_end,
                      va->va_end - va->va_start);
--

2.21.0

--
Vlad Rezki