Stop wasting time on malloc in snprintf_zstd_header

Profiling zdb -vvvvv on datasets with a lot of zstd blocks, we find ourselves spending quite a lot of time on malloc/free, because we allocate a 16M abd each call, and never free it, so we're leaking 16M per call as well. This seems sub-optimal. So let's just keep the buffer around and reuse it. Reviewed-by: Brian Behlendorf <[email protected]> Reviewed-by: Rob Norris <[email protected]> Signed-off-by: Rich Ercolani <[email protected]> Closes #15721
openzfs · Jan 29, 2024 · 4d4972e · 4d4972e
1 parent 3425484
commit 4d4972e
Showing 1 changed file with 3 additions and 2 deletions.
diff --git a/cmd/zdb/zdb.c b/cmd/zdb/zdb.c
@@ -2360,7 +2360,7 @@ static void
 snprintf_zstd_header(spa_t *spa, char *blkbuf, size_t buflen,
     const blkptr_t *bp)
 {
-	abd_t *pabd;
+	static abd_t *pabd = NULL;
 	void *buf;
 	zio_t *zio;
 	zfs_zstdhdr_t zstd_hdr;
@@ -2391,7 +2391,8 @@ snprintf_zstd_header(spa_t *spa, char *blkbuf, size_t buflen,
 		return;
 	}
 
-	pabd = abd_alloc_for_io(SPA_MAXBLOCKSIZE, B_FALSE);
+	if (!pabd)
+		pabd = abd_alloc_for_io(SPA_MAXBLOCKSIZE, B_FALSE);
 	zio = zio_root(spa, NULL, NULL, 0);
 
 	/* Decrypt but don't decompress so we can read the compression header */