Commit 30a7a9b1 authored by Baoquan He's avatar Baoquan He Committed by Andrew Morton
Browse files

mm/vmalloc: skip the uninitilized vmalloc areas 

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
VM_UNINITIALIZED.

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.

Link: https://lkml.kernel.org/r/20230206084020.174506-6-bhe@redhat.com


Signed-off-by: default avatarBaoquan He <bhe@redhat.com>
Reviewed-by: default avatarLorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: default avatarUladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Dan Carpenter <error27@gmail.com>
Cc: Stephen Brennan <stephen.s.brennan@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent bba9697b

mm/vmalloc.c

+5 −0
Original line number Diff line number Diff line
@@ -3587,6 +3587,11 @@ 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);