[Devel] [PATCH VZ9] dm-qcow2-map: disable high-order allocation warning

[Andrey Zhadchenko]

Since 4M GFP_NOIO is out of reach, we can just pre-alloc the required 
memory.
In current iteration all reads are processed from one work item. Seems 
like process_compressed_read() uses buffer only in the scope of it's 
function, without submitting any io with it. Therefore there is no 
concurrency and allocating a single buffer (probably kvmalloc will do 
too) during alloc_qcow2_target() will do the trick for us.

On 11/11/24 08:37, Pavel Tikhomirov wrote:
> Disable the warning:
> 
> kernel: order 10 >= 10, gfp 0x40c00
> kernel: WARNING: CPU: 5 PID: 182 at mm/page_alloc.c:5630 __alloc_pages+0x1d7/0x3f0
> kernel: process_compressed_read+0x6f/0x590 [dm_qcow2]
> 
> As with 1M clusters and in case of zstd compression the buffer size
> (clu_size + sizeof(ZSTD_DCtx) + ZSTD_BLOCKSIZE_MAX + clu_size +
> ZSTD_BLOCKSIZE_MAX + 64 = 2520776) can only fit into 4M (10-th order)
> allocation.
> 
> https://virtuozzo.atlassian.net/browse/VSTOR-94596
> Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
> 
> Feature: dm-qcow2: ZSTD decompression
> ---
>   drivers/md/dm-qcow2-map.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/md/dm-qcow2-map.c b/drivers/md/dm-qcow2-map.c
> index 6585f3fac6e7b..18f9442493831 100644
> --- a/drivers/md/dm-qcow2-map.c
> +++ b/drivers/md/dm-qcow2-map.c
> @@ -3671,7 +3671,7 @@ static void process_compressed_read(struct qcow2 *qcow2, struct list_head *read_
>   		dctxlen = zlib_inflate_workspacesize();
>   
>   
> -	buf = kmalloc(qcow2->clu_size + dctxlen, GFP_NOIO);
> +	buf = kmalloc(qcow2->clu_size + dctxlen, GFP_NOIO | __GFP_ORDER_NOWARN);
>   	if (!buf) {
>   		end_qios(read_list, BLK_STS_RESOURCE);
>   		return;