[PATCH 6.9.y] erofs: avoid allocating DEFLATE streams before mounting

[Gao Xiang]

Hi Greg,

ping? Do these backport fixes miss the 6.6, 6.8, 6.9 queues..

Thanks,
Gao XIang

On 2024/5/30 17:21, Gao Xiang wrote:
> commit 80eb4f62056d6ae709bdd0636ab96ce660f494b2 upstream.
> 
> Currently, each DEFLATE stream takes one 32 KiB permanent internal
> window buffer even if there is no running instance which uses DEFLATE
> algorithm.
> 
> It's unexpected and wasteful on embedded devices with limited resources
> and servers with hundreds of CPU cores if DEFLATE is enabled but unused.
> 
> Fixes: ffa09b3bd024 ("erofs: DEFLATE compression support")
> Cc: <stable at vger.kernel.org> # 6.6+
> Reviewed-by: Sandeep Dhavale <dhavale at google.com>
> Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>
> Link: https://lore.kernel.org/r/20240520090106.2898681-1-hsiangkao@linux.alibaba.com
> ---
>   fs/erofs/decompressor_deflate.c | 55 +++++++++++++++++----------------
>   1 file changed, 29 insertions(+), 26 deletions(-)
> 
> diff --git a/fs/erofs/decompressor_deflate.c b/fs/erofs/decompressor_deflate.c
> index 81e65c453ef0..3a3461561a3c 100644
> --- a/fs/erofs/decompressor_deflate.c
> +++ b/fs/erofs/decompressor_deflate.c
> @@ -46,39 +46,15 @@ int __init z_erofs_deflate_init(void)
>   	/* by default, use # of possible CPUs instead */
>   	if (!z_erofs_deflate_nstrms)
>   		z_erofs_deflate_nstrms = num_possible_cpus();
> -
> -	for (; z_erofs_deflate_avail_strms < z_erofs_deflate_nstrms;
> -	     ++z_erofs_deflate_avail_strms) {
> -		struct z_erofs_deflate *strm;
> -
> -		strm = kzalloc(sizeof(*strm), GFP_KERNEL);
> -		if (!strm)
> -			goto out_failed;
> -
> -		/* XXX: in-kernel zlib cannot shrink windowbits currently */
> -		strm->z.workspace = vmalloc(zlib_inflate_workspacesize());
> -		if (!strm->z.workspace) {
> -			kfree(strm);
> -			goto out_failed;
> -		}
> -
> -		spin_lock(&z_erofs_deflate_lock);
> -		strm->next = z_erofs_deflate_head;
> -		z_erofs_deflate_head = strm;
> -		spin_unlock(&z_erofs_deflate_lock);
> -	}
>   	return 0;
> -
> -out_failed:
> -	erofs_err(NULL, "failed to allocate zlib workspace");
> -	z_erofs_deflate_exit();
> -	return -ENOMEM;
>   }
>   
>   int z_erofs_load_deflate_config(struct super_block *sb,
>   			struct erofs_super_block *dsb, void *data, int size)
>   {
>   	struct z_erofs_deflate_cfgs *dfl = data;
> +	static DEFINE_MUTEX(deflate_resize_mutex);
> +	static bool inited;
>   
>   	if (!dfl || size < sizeof(struct z_erofs_deflate_cfgs)) {
>   		erofs_err(sb, "invalid deflate cfgs, size=%u", size);
> @@ -89,9 +65,36 @@ int z_erofs_load_deflate_config(struct super_block *sb,
>   		erofs_err(sb, "unsupported windowbits %u", dfl->windowbits);
>   		return -EOPNOTSUPP;
>   	}
> +	mutex_lock(&deflate_resize_mutex);
> +	if (!inited) {
> +		for (; z_erofs_deflate_avail_strms < z_erofs_deflate_nstrms;
> +		     ++z_erofs_deflate_avail_strms) {
> +			struct z_erofs_deflate *strm;
> +
> +			strm = kzalloc(sizeof(*strm), GFP_KERNEL);
> +			if (!strm)
> +				goto failed;
> +			/* XXX: in-kernel zlib cannot customize windowbits */
> +			strm->z.workspace = vmalloc(zlib_inflate_workspacesize());
> +			if (!strm->z.workspace) {
> +				kfree(strm);
> +				goto failed;
> +			}
>   
> +			spin_lock(&z_erofs_deflate_lock);
> +			strm->next = z_erofs_deflate_head;
> +			z_erofs_deflate_head = strm;
> +			spin_unlock(&z_erofs_deflate_lock);
> +		}
> +		inited = true;
> +	}
> +	mutex_unlock(&deflate_resize_mutex);
>   	erofs_info(sb, "EXPERIMENTAL DEFLATE feature in use. Use at your own risk!");
>   	return 0;
> +failed:
> +	mutex_unlock(&deflate_resize_mutex);
> +	z_erofs_deflate_exit();
> +	return -ENOMEM;
>   }
>   
>   int z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,