[PATCH 3/3] malloc: revert file-backed mmap, sbrk for main arena

[Eric Wong <e@80x24.org>]

With the effectiveness of anti-fragmentation size classes and
subsequent memory reduction, the non-growable file-backed mmap
to be the backing store makes little sense.
---
 dlmalloc_c.h | 13 ++++++------
 mymalloc.h   | 56 ++--------------------------------------------------
 2 files changed, 9 insertions(+), 60 deletions(-)

diff --git a/dlmalloc_c.h b/dlmalloc_c.h
index 348c194..5aa9e94 100644
--- a/dlmalloc_c.h
+++ b/dlmalloc_c.h
@@ -4319,11 +4319,9 @@ static int sys_trim(mstate m, size_t pad) {
               !has_segment_link(m, sp)) { /* can't shrink if pinned */
             size_t newsize = sp->size - extra;
             (void)newsize; /* placate people compiling -Wunused-variable */
-            /*
-             * dlmalloc preferred mremap, here, but mwrap uses a file-backed
-             * mmap for small allocations on Linux and we close the FD ASAP.
-             */
-            if (CALL_MUNMAP(sp->base + newsize, extra) == 0) {
+            /* Prefer mremap, fall back to munmap */
+            if ((CALL_MREMAP(sp->base, sp->size, newsize, 0) != MFAIL) ||
+                (CALL_MUNMAP(sp->base + newsize, extra) == 0)) {
               released = extra;
             }
           }
@@ -5422,7 +5420,10 @@ static mstate init_user_mstate(char* tbase, size_t tsize) {
   m->magic = mparams.magic;
   m->release_checks = MAX_RELEASE_CHECK_RATE;
   m->mflags = mparams.default_mflags;
-  disable_contiguous(m);
+  static int once;
+#	define MP_FIRST_TIME (uatomic_cmpxchg(&once, 0, 1) == 0)
+  if (!MP_FIRST_TIME)
+    disable_contiguous(m);
   init_bins(m);
   mn = next_chunk(mem2chunk(m));
   init_top(m, mn, (size_t)((tbase + tsize) - (char*)mn) - TOP_FOOT_SIZE);
diff --git a/mymalloc.h b/mymalloc.h
index 44c5dd3..4dd2ee6 100644
--- a/mymalloc.h
+++ b/mymalloc.h
@@ -40,68 +40,16 @@
 #include <urcu/rculist.h>
 #include <urcu/wfcqueue.h>
 #include <urcu-bp.h>
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <fcntl.h>
-#include <errno.h>
-
-/* this is fine on most x86-64, especially with file-backed mmap(2) */
-#define DEFAULT_GRANULARITY (64U * 1024U * 1024U)
-
-#if !defined(MWRAP_FILE_BACKED) && defined(__linux__) && defined(O_TMPFILE)
-#	define MWRAP_FILE_BACKED 1
-#else
-#	define MWRAP_FILE_BACKED 0
-#endif
-#if MWRAP_FILE_BACKED
-#	include <sys/mman.h>
-static void *my_mmap(size_t size)
-{
-	int flags = MAP_PRIVATE;
-	const char *tmpdir = getenv("TMPDIR");
-	int fd;
-	void *ret;
-
-	if (!tmpdir)
-		tmpdir = "/tmp";
-
-	fd = open(tmpdir, O_TMPFILE|O_RDWR|S_IRUSR|S_IWUSR, 0600);
-	if (fd < 0) {
-		flags |= MAP_ANONYMOUS;
-	} else {
-		int t = ftruncate(fd, size); /* sparse file */
-
-		if (t < 0) {
-			flags |= MAP_ANONYMOUS;
-			close(fd);
-			fd = -1;
-		}
-	}
-	ret = mmap(NULL, size, PROT_READ|PROT_WRITE, flags, fd, 0);
-	if (fd >= 0) {
-		int err = errno;
-		close(fd);
-		errno = err;
-	}
-	return ret;
-}
-#endif /* MWRAP_FILE_BACKED */
 
 /* knobs for dlmalloc */
+#define HAVE_MORECORE 1
+#define DEFAULT_GRANULARITY (2U * 1024U * 1024U)
 #define FOOTERS 1 /* required for remote_free_* stuff */
 #define USE_DL_PREFIX
 #define ONLY_MSPACES 1 /* aka per-thread "arenas" */
 #define DLMALLOC_EXPORT static inline
 /* #define NO_MALLOC_STATS 1 */
 #define USE_LOCKS 0 /* we do our own global_mtx + ms_tsd */
-#if MWRAP_FILE_BACKED
-#	define MMAP(size) my_mmap(size)
-/*
- * we use anonymous mmap (via DIRECT_MMAP) and mremap since it benefits
- * large allocations which require resizing (open-addressed hash tables,
- * large string buffers, etc)
- */
-#endif
 #include "dlmalloc_c.h"
 #undef ABORT /* conflicts with Perl */
 #undef NOINLINE /* conflicts with Ruby, defined by dlmalloc_c.h */