On Fri, Jan 13, 2023 at 11:19:19AM +0800, Baoquan He wrote: > 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@xxxxxxxxxx> > --- > 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 > Reviewed-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
