Re: [PATCH] smb: client: use kvzalloc() for megabyte buffer in simple fallocate

[Steve French]

merged into cifs-2.6.git for-next

On Sat, Jul 11, 2026 at 9:55 PM Fredric Cover
<fredric.cover.lkernel@xxxxxxxxx> wrote:
>
> From: Fredric Cover <fredric.cover.lkernel@xxxxxxxxx>
>
> Currently in smb3_simple_fallocate_range(), a 1 MB buffer is allocated
> using kzalloc(). Under heavy memory fragmentation, a contiguous 1 MB block
> of physical memory (an order-8 allocation) may not be available,
> causing the allocation to fail.
>
> This failure was observed during xfstests generic/013 on a 4GB RAM
> test machine running fsstress:
>
> fsstress: page allocation failure: order:8,
> mode:0x40dc0(GFP_KERNEL|__GFP_ZERO|__GFP_COMP),
> nodemask=(null),cpuset=/,mems_allowed=0
>
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x5d/0x80
>  warn_alloc+0x163/0x190
>  __alloc_pages_slowpath.constprop.0+0x71b/0x12f0
>  __alloc_frozen_pages_noprof+0x2f6/0x340
>  alloc_pages_mpol+0xb6/0x170
>  ___kmalloc_large_node+0xb3/0xd0
>  __kmalloc_large_noprof+0x1e/0xc0
>  smb3_simple_falloc.isra.0+0x62b/0x960
>  cifs_fallocate+0xed/0x180
>  vfs_fallocate+0x165/0x3c0
>  __x64_sys_fallocate+0x48/0xa0
>  do_syscall_64+0xe1/0x640
>  entry_SYSCALL_64_after_hwframe+0x76/0x7e
>  </TASK>
>
> Node 0 Normal: 3375*4kB ... 7*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB
>
> Since this scratch buffer does not require physically contiguous memory,
> switch the allocation to kvzalloc(). This retains the performance
> benefits of kmalloc() under normal conditions, while gracefully falling
> back to virtually contiguous memory when physical allocation fails.
>
> Fixes: 966a3cb7c7db ("cifs: improve fallocate emulation")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Fredric Cover <fredric.cover.lkernel@xxxxxxxxx>
> Tested-by: Fredric Cover <fredric.cover.lkernel@xxxxxxxxx>
> ---
>  fs/smb/client/smb2ops.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
> index d4875f9532b4..55b53bb9e3fd 100644
> --- a/fs/smb/client/smb2ops.c
> +++ b/fs/smb/client/smb2ops.c
> @@ -3595,7 +3595,7 @@ static int smb3_simple_fallocate_range(unsigned int xid,
>         if (rc)
>                 goto out;
>
> -       buf = kzalloc(1024 * 1024, GFP_KERNEL);
> +       buf = kvzalloc(1024 * 1024, GFP_KERNEL);
>         if (buf == NULL) {
>                 rc = -ENOMEM;
>                 goto out;
> @@ -3652,7 +3652,7 @@ static int smb3_simple_fallocate_range(unsigned int xid,
>
>   out:
>         kfree(out_data);
> -       kfree(buf);
> +       kvfree(buf);
>         return rc;
>  }
>
> --
> 2.53.0
>
>


-- 
Thanks,

Steve