xmmap: inform Linux users of tuning knobs on ENOMEM

Linux users may benefit from additional information on how to
avoid ENOMEM from mmap despite the system having enough RAM to
accomodate them.  We can't reliably unmap pack windows to work
around the issue since malloc and other library routines may
mmap without our knowledge.

Signed-off-by: Eric Wong <e@80x24.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 15 insertions, 1 deletions

diff --git a/object-file.c b/object-file.c
index f233b440b2..b9c3219793 100644
--- a/object-file.c
+++ b/object-file.c
@@ -1023,12 +1023,26 @@ void *xmmap_gently(void *start, size_t length,
 	return ret;
 }
 
+const char *mmap_os_err(void)
+{
+	static const char blank[] = "";
+#if defined(__linux__)
+	if (errno == ENOMEM) {
+		/* this continues an existing error message: */
+		static const char enomem[] =
+", check sys.vm.max_map_count and/or RLIMIT_DATA";
+		return enomem;
+	}
+#endif /* OS-specific bits */
+	return blank;
+}
+
 void *xmmap(void *start, size_t length,
 	int prot, int flags, int fd, off_t offset)
 {
 	void *ret = xmmap_gently(start, length, prot, flags, fd, offset);
 	if (ret == MAP_FAILED)
-		die_errno(_("mmap failed"));
+		die_errno(_("mmap failed%s"), mmap_os_err());
 	return ret;
 }