Subject: Re: [PATCH 5/6] nvram: Slim down zlib_deflate workspace when possible

From: Benjamin Herrenschmidt <[email-masked]>
Date: Mon, 07 Feb 2011 15:39:35 +1100

On Sat, 2010-11-13 at 20:15 -0800, Jim Keniston wrote:
> Instead of always creating a huge (268K) deflate_workspace with the
> maximum compression parameters (windowBits=15, memLevel=8), allow the
> caller to obtain a smaller workspace (24K in our case) by specifying
> smaller parameter values -- via zlib_deflate_workspacesize2(). In our
> case, a small workspace is a win because our choices are to allocate
> the workspace when we need it (i.e., during an oops or panic) or
> allocate it at boot time.  (We do the latter.)
> 
> Signed-off-by: Jim Keniston <[email-masked]>
> ---

Can you submit that to lkml please ? CC Linus and Andrew (or send to
Andrew/Linus and CC lkml). This change shouldn't go via the powerpc tree
since it changes the generic zlib code.

I'm dropping 5/6 and 6/6 for now... still reviewing the rest.

Cheers,
Ben.

>  include/linux/zlib.h            |   14 ++++++++++++--
>  lib/zlib_deflate/deflate.c      |   33 ++++++++++++++++++++++++++++++++-
>  lib/zlib_deflate/deflate_syms.c |    1 +
>  lib/zlib_deflate/defutil.h      |   17 +++++++++++++----
>  4 files changed, 58 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/zlib.h b/include/linux/zlib.h
> index 40c49cb..3f15036 100644
> --- a/include/linux/zlib.h
> +++ b/include/linux/zlib.h
> @@ -179,11 +179,21 @@ typedef z_stream *z_streamp;
>  
>                          /* basic functions */
>  
> +extern int zlib_deflate_workspacesize2 (int windowBits, int memLevel);
> +/*
> +   Returns the number of bytes that needs to be allocated for a per-
> +   stream workspace with the specified parameters.  A pointer to this
> +   number of bytes should be returned in stream->workspace before
> +   calling zlib_deflateInit2(); and the windowBits and memLevel
> +   parameters passed to zlib_deflateInit2() must not exceed those
> +   passed here.
> +*/
> +
>  extern int zlib_deflate_workspacesize (void);
>  /*
>     Returns the number of bytes that needs to be allocated for a per-
> -   stream workspace.  A pointer to this number of bytes should be
> -   returned in stream->workspace before calling zlib_deflateInit().
> +   stream workspace with the default (large) windowBits and memLevel
> +   parameters.
>  */
>  
>  /* 
> diff --git a/lib/zlib_deflate/deflate.c b/lib/zlib_deflate/deflate.c
> index 46a31e5..cdb207a 100644
> --- a/lib/zlib_deflate/deflate.c
> +++ b/lib/zlib_deflate/deflate.c
> @@ -176,6 +176,7 @@ int zlib_deflateInit2(
>      deflate_state *s;
>      int noheader = 0;
>      deflate_workspace *mem;
> +    char *next;
>  
>      ush *overlay;
>      /* We overlay pending_buf and d_buf+l_buf. This works since the average
> @@ -199,6 +200,21 @@ int zlib_deflateInit2(
>  	strategy < 0 || strategy > Z_HUFFMAN_ONLY) {
>          return Z_STREAM_ERROR;
>      }
> +
> +    /*
> +     * Direct the workspace's pointers to the chunks that were allocated
> +     * along with the deflate_workspace struct.
> +     */
> +    next = (char *) mem;
> +    next += sizeof(*mem);
> +    mem->window_memory = (Byte *) next;
> +    next += zlib_deflate_window_memsize(windowBits);
> +    mem->prev_memory = (Pos *) next;
> +    next += zlib_deflate_prev_memsize(windowBits);
> +    mem->head_memory = (Pos *) next;
> +    next += zlib_deflate_head_memsize(memLevel);
> +    mem->overlay_memory = next;
> +
>      s = (deflate_state *) &(mem->deflate_memory);
>      strm->state = (struct internal_state *)s;
>      s->strm = strm;
> @@ -1249,5 +1265,20 @@ static block_state deflate_slow(
>  
>  int zlib_deflate_workspacesize(void)
>  {
> -    return sizeof(deflate_workspace);
> +    return zlib_deflate_workspacesize2(MAX_WBITS, MAX_MEM_LEVEL);
> +}
> +
> +int zlib_deflate_workspacesize2(int windowBits, int memLevel)
> +{
> +    if (windowBits < 0) /* undocumented feature: suppress zlib header */
> +        windowBits = -windowBits;
> +    if (memLevel < 1 || memLevel > MAX_MEM_LEVEL ||
> +        windowBits < 9 || windowBits > 15)
> +        return -1;
> +
> +    return sizeof(deflate_workspace)
> +        + zlib_deflate_window_memsize(windowBits)
> +        + zlib_deflate_prev_memsize(windowBits)
> +        + zlib_deflate_head_memsize(memLevel)
> +        + zlib_deflate_overlay_memsize(memLevel);
>  }
> diff --git a/lib/zlib_deflate/deflate_syms.c b/lib/zlib_deflate/deflate_syms.c
> index ccfe25f..cdf1cdd 100644
> --- a/lib/zlib_deflate/deflate_syms.c
> +++ b/lib/zlib_deflate/deflate_syms.c
> @@ -11,6 +11,7 @@
>  #include <linux/zlib.h>
>  
>  EXPORT_SYMBOL(zlib_deflate_workspacesize);
> +EXPORT_SYMBOL(zlib_deflate_workspacesize2);
>  EXPORT_SYMBOL(zlib_deflate);
>  EXPORT_SYMBOL(zlib_deflateInit2);
>  EXPORT_SYMBOL(zlib_deflateEnd);
> diff --git a/lib/zlib_deflate/defutil.h b/lib/zlib_deflate/defutil.h
> index 6b15a90..b640b64 100644
> --- a/lib/zlib_deflate/defutil.h
> +++ b/lib/zlib_deflate/defutil.h
> @@ -241,12 +241,21 @@ typedef struct deflate_state {
>  typedef struct deflate_workspace {
>      /* State memory for the deflator */
>      deflate_state deflate_memory;
> -    Byte window_memory[2 * (1 << MAX_WBITS)];
> -    Pos prev_memory[1 << MAX_WBITS];
> -    Pos head_memory[1 << (MAX_MEM_LEVEL + 7)];
> -    char overlay_memory[(1 << (MAX_MEM_LEVEL + 6)) * (sizeof(ush)+2)];
> +    Byte *window_memory;
> +    Pos *prev_memory;
> +    Pos *head_memory;
> +    char *overlay_memory;
>  } deflate_workspace;
>  
> +#define zlib_deflate_window_memsize(windowBits) \
> +	(2 * (1 << (windowBits)) * sizeof(Byte))
> +#define zlib_deflate_prev_memsize(windowBits) \
> +	((1 << (windowBits)) * sizeof(Pos))
> +#define zlib_deflate_head_memsize(memLevel) \
> +	((1 << ((memLevel)+7)) * sizeof(Pos))
> +#define zlib_deflate_overlay_memsize(memLevel) \
> +	((1 << ((memLevel)+6)) * (sizeof(ush)+2))
> +
>  /* Output a byte on the stream.
>   * IN assertion: there is enough room in pending_buf.
>   */
> 
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