Re: [PATCH 1/4] zstd: pass pointer rathen than structure to functions

[David Sterba]

On Tue, Jun 04, 2019 at 03:43:26PM -0700, Andrew Morton wrote:
> On Mon,  3 Jun 2019 14:32:03 +0530 Maninder Singh <maninder1.s@xxxxxxxxxxx> wrote:
> 
> > currently params structure is passed in all functions, which increases
> > stack usage in all the function and lead to stack overflow on target like
> > ARM with kernel stack size of 8 KB so better to pass pointer.
> > 
> > Checked for ARM:
> > 
> >                                 Original               Patched
> > Call FLow Size:                  1264                   1040
> > ....
> > (HUF_sort)                      -> 296
> > (HUF_buildCTable_wksp)          -> 144
> > (HUF_compress4X_repeat)         -> 88
> > (ZSTD_compressBlock_internal)   -> 200
> > (ZSTD_compressContinue_internal)-> 136                  -> 88
> > (ZSTD_compressCCtx)             -> 192                  -> 64
> > (zstd_compress)                 -> 144                  -> 96
> > (crypto_compress)               -> 32
> > (zcomp_compress)                -> 32
> > ....
> > 
> > Signed-off-by: Maninder Singh <maninder1.s@xxxxxxxxxxx>
> > Signed-off-by: Vaneet Narang <v.narang@xxxxxxxxxxx>
> > 
> 
> You missed btrfs.  This needs review, please - particularly the
> kernel-wide static ZSTD_parameters in zstd_get_btrfs_parameters().

> 
> The base patch is here:
> 
> http://lkml.kernel.org/r/1559552526-4317-2-git-send-email-maninder1.s@xxxxxxxxxxx  
> 
> --- a/fs/btrfs/zstd.c~zstd-pass-pointer-rathen-than-structure-to-functions-fix
> +++ a/fs/btrfs/zstd.c
> @@ -27,15 +27,17 @@
>  /* 307s to avoid pathologically clashing with transaction commit */
>  #define ZSTD_BTRFS_RECLAIM_JIFFIES (307 * HZ)
>  
> -static ZSTD_parameters zstd_get_btrfs_parameters(unsigned int level,
> +static ZSTD_parameters *zstd_get_btrfs_parameters(unsigned int level,
>  						 size_t src_len)
>  {
> -	ZSTD_parameters params = ZSTD_getParams(level, src_len, 0);
> +	static ZSTD_parameters params;

> +
> +	params = ZSTD_getParams(level, src_len, 0);

No thats' broken, the params can't be static as it depends on level and
src_len. What happens if there are several requests in parallel with
eg. different levels?

Would be really great if the mailinglist is CCed when the code is
changed in a non-trivial way.