patches/old/mm-vmalloc-skip-the-uninitilized-vmalloc-areas.patch

From: Baoquan He <bhe@redhat.com>
Subject: mm/vmalloc: skip the uninitilized vmalloc areas
Date: Mon, 6 Feb 2023 16:40:18 +0800

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: Baoquan He <bhe@redhat.com>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Dan Carpenter <error27@gmail.com>
Cc: Stephen Brennan <stephen.s.brennan@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/vmalloc.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/mm/vmalloc.c~mm-vmalloc-skip-the-uninitilized-vmalloc-areas
+++ a/mm/vmalloc.c
@@ -3587,6 +3587,11 @@ long vread(char *buf, char *addr, unsign
 		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);
 
_