[PATCH v3 5/7] mm/vmalloc: skip the uninitilized vmalloc areas

Baoquan He
2023-01-13T03:21:03Z

For areas allocated via vmalloc_xxx() APIs, it searches for unmapped area
to reserve and allocates new pages to map into, please see function
__vmalloc_node_range(). During the process, flag VM_UNINITIALIZED is set
in vm->flags to indicate that the pages allocation and mapping haven't
been done, until clear_vm_uninitialized_flag() is called to clear it.

For this kind of area, if VM_UNINITIALIZED is still set, let's ignore
it in vread() because pages newly allocated and being mapped in that
area only contains zero data. reading them out by aligned_vread() is
wasting time.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
mm/vmalloc.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 4a10b3b692fa..dbcdcad2276b 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3660,6 +3660,11 @@ long vread(char *buf, char *addr, unsigned long count)
if (!vm && !flags)
continue;

+ if (vm && (vm->flags & VM_UNINITIALIZED))
+ continue;
+ /* Pair with smp_wmb() in clear_vm_uninitialized_flag() */
+ smp_rmb();
+
vaddr = (char *) va->va_start;
size = vm ? get_vm_area_size(vm) : va_size(va);

--
2.34.1