diff --git a/Documentation/config.txt b/Documentation/config.txt
index 178e0e1e209e066ad220d6ba95be0728c2db5e99..28fe6942cf867549e8d19120e339a14cb8347b1b 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -118,6 +118,15 @@ core.legacyheaders::
 	database directly (where the "http://" and "rsync://" protocols
 	count as direct access).
 
+core.packedGitLimit::
+	Maximum number of bytes to map simultaneously into memory
+	from pack files.  If Git needs to access more than this many
+	bytes at once to complete an operation it will unmap existing
+	regions to reclaim virtual address space within the process.
+	Default is 256 MiB, which should be reasonable for all
+	users/operating systems, except on largest Git projects.
+	You probably do not need to adjust this value.
+
 alias.*::
 	Command aliases for the gitlink:git[1] command wrapper - e.g.
 	after defining "alias.last = cat-file commit HEAD", the invocation
diff --git a/cache.h b/cache.h
index e0a26e9d04857484f07bd49f740e653085129447..816239bea0fbf53852efcb3575995cd5aef7e445 100644
--- a/cache.h
+++ b/cache.h
@@ -196,6 +196,7 @@ extern int warn_ambiguous_refs;
 extern int shared_repository;
 extern const char *apply_default_whitespace;
 extern int zlib_compression_level;
+extern size_t packed_git_limit;
 
 #define GIT_REPO_VERSION 0
 extern int repository_format_version;
diff --git a/config.c b/config.c
index fcccf7e2a4f3b7487af10d4f7b505c7ef492b9e8..0c21286cb25d6a0d1f4dca4e82e59dcb7165e0d5 100644
--- a/config.c
+++ b/config.c
@@ -298,6 +298,11 @@ int git_default_config(const char *var, const char *value)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.packedgitlimit")) {
+		packed_git_limit = git_config_int(var, value);
+		return 0;
+	}
+
 	if (!strcmp(var, "user.name")) {
 		strlcpy(git_default_name, value, sizeof(git_default_name));
 		return 0;
diff --git a/environment.c b/environment.c
index a1502c4e87c0067c8cc276006317005a0da21a49..a3ddae68a7bada16edfa88d8f9244181af8e7cea 100644
--- a/environment.c
+++ b/environment.c
@@ -23,6 +23,7 @@ char *git_log_output_encoding;
 int shared_repository = PERM_UMASK;
 const char *apply_default_whitespace;
 int zlib_compression_level = Z_DEFAULT_COMPRESSION;
+size_t packed_git_limit = 256 * 1024 * 1024;
 int pager_in_use;
 int pager_use_color = 1;
 
diff --git a/sha1_file.c b/sha1_file.c
index 4824a5d4d8bb5104461ea8245d9a22b5408cb537..4183f595edfe6086f5097a430cb48202db00c5c1 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -397,7 +397,6 @@ static char *find_sha1_file(const unsigned char *sha1, struct stat *st)
 	return NULL;
 }
 
-#define PACK_MAX_SZ (1<<26)
 static int pack_used_ctr;
 static unsigned long pack_mapped;
 struct packed_git *packed_git;
@@ -490,7 +489,7 @@ int use_packed_git(struct packed_git *p)
 		struct pack_header *hdr;
 
 		pack_mapped += p->pack_size;
-		while (PACK_MAX_SZ < pack_mapped && unuse_one_packed_git())
+		while (packed_git_limit < pack_mapped && unuse_one_packed_git())
 			; /* nothing */
 		fd = open(p->pack_name, O_RDONLY);
 		if (fd < 0)