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

Lorenzo Stoakes
2023-01-16T12:24:53Z

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@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
>

Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>