mm/vmalloc: modify struct vmap_area to reduce its size

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.

Link: http://lkml.kernel.org/r/20190716152656.12255-3-lpf.vector@gmail.com
Signed-off-by: Pengfei Li <lpf.vector@gmail.com>
Suggested-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 14 deletions

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index d535ef125bda..f095843fc243 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -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 @@ retry:
 
         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);
@@ -1928,7 +1927,6 @@ 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;
@@ -2026,7 +2024,6 @@ 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);
 }
 
@@ -2131,10 +2128,10 @@ 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;
 }
 
 /**
@@ -2155,11 +2152,10 @@ 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);
@@ -2862,7 +2858,7 @@ 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;
@@ -2942,7 +2938,7 @@ 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;
@@ -3485,10 +3481,10 @@ 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.
+         * s_show can encounter race with remove_vm_area, !vm on behalf
+         * of vmap area is being tear down or vm_map_ram allocation.
          */
-        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);