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, 29 insertions, 2 deletions

diff --git a/lib/zlib_deflate/deflate.c b/lib/zlib_deflate/deflate.c
index 46a31e5f49c3..d63381e8e333 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;
@@ -1247,7 +1263,18 @@ static block_state deflate_slow(
     return flush == Z_FINISH ? finish_done : block_done;
 }
 
-int zlib_deflate_workspacesize(void)
+int zlib_deflate_workspacesize(int windowBits, int memLevel)
 {
-    return sizeof(deflate_workspace);
+    if (windowBits < 0) /* undocumented feature: suppress zlib header */
+        windowBits = -windowBits;
+
+    /* Since the return value is typically passed to vmalloc() unchecked... */
+    BUG_ON(memLevel < 1 || memLevel > MAX_MEM_LEVEL || windowBits < 9 ||
+                                                        windowBits > 15);
+
+    return sizeof(deflate_workspace)
+        + zlib_deflate_window_memsize(windowBits)
+        + zlib_deflate_prev_memsize(windowBits)
+        + zlib_deflate_head_memsize(memLevel)
+        + zlib_deflate_overlay_memsize(memLevel);
 }