zlib: slim down zlib_deflate() workspace when possible

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 by specifying smaller parameter
values.

For example, when capturing oops and panic reports to a medium with
limited capacity, such as NVRAM, compression may be the only way to
capture the whole report.  In this case, a small workspace (24K works
fine) is a win, whether you allocate the workspace when you need it (i.e.,
during an oops or panic) or at boot time.

I've verified that this patch works with all accepted values of windowBits
(positive and negative), memLevel, and compression level.

Signed-off-by: Jim Keniston <jkenisto@us.ibm.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: David Miller <davem@davemloft.net>
Cc: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 3 deletions

diff --git a/include/linux/zlib.h b/include/linux/zlib.h
index 40c49cb3eb51..9c5a6b4de0a3 100644
--- a/include/linux/zlib.h
+++ b/include/linux/zlib.h
@@ -179,11 +179,16 @@ typedef z_stream *z_streamp;
 
                         /* basic functions */
 
-extern int zlib_deflate_workspacesize (void);
+extern int zlib_deflate_workspacesize (int windowBits, int memLevel);
 /*
    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 specified parameters.  A pointer to this
+   number of bytes should be returned in stream->workspace before
+   you call zlib_deflateInit() or zlib_deflateInit2().  If you call
+   zlib_deflateInit(), specify windowBits = MAX_WBITS and memLevel =
+   MAX_MEM_LEVEL here.  If you call zlib_deflateInit2(), the windowBits
+   and memLevel parameters passed to zlib_deflateInit2() must not
+   exceed those passed here.
 */
 
 /*