mdbx: add MDBX_DBG_NOFALLOC_INCORE.

It is a workaround to sporadic test failures due to lack of space in tmpfs and/or free memory.

mdbx.h

@@ -929,8 +929,12 @@ typedef enum MDBX_debug_flags {
    * \note Nonetheless a new write transactions will use and store the last signature regardless this flag */
   MDBX_DBG_DONT_UPGRADE = 64,
 
+  /** Disables the use of fallocate() for an in-core database(s) to avoid sporadic test failures
+   *  due to lack of space in tmpfs and/or free memory. */
+  MDBX_DBG_NOFALLOC_INCORE = 128,
+
 #ifdef ENABLE_UBSAN
-  MDBX_DBG_MAX = ((unsigned)MDBX_LOG_MAX) << 16 | 127 /* avoid UBSAN false-positive trap by a tests */,
+  MDBX_DBG_MAX = ((unsigned)MDBX_LOG_MAX) << 16 | 255 /* avoid UBSAN false-positive trap by a tests */,
 #endif /* ENABLE_UBSAN */
 
   /** for mdbx_setup_debug() only: Don't change current settings */

src/bits.md

@@ -10,7 +10,7 @@ N |   MASK  | ENV       | TXN          | DB       | PUT       | DBI        | NOD
 7 |0000 0080|           |TXN_DRAINED_GC|DB_VALID  |ALLDUPS    |DBI_LINDO   |         |          |         |
 8 |0000 0100| _MAY_MOVE |TXN_CURSORS   |          |           |            |         |          | <=      |
 9 |0000 0200| _MAY_UNMAP|              |          |           |            |         |          | <=      |
-10|0000 0400|           |              |          |           |            |         |          |         |
+10|0000 0400| _NO_FALLOC|              |          |           |            |         |          | <=      |
 11|0000 0800|           |              |          |           |            |         |          |         |
 12|0000 1000|           |              |          |           |            |         |          |         |
 13|0000 2000|VALIDATION |              |          |           |            |         |P_SPILLED |         |

src/cogs.h

@@ -522,6 +522,10 @@ MDBX_INTERNAL void munlock_after(const MDBX_env *env, const pgno_t aligned_pgno,
 
 MDBX_INTERNAL void munlock_all(const MDBX_env *env);
 
+static inline bool fallocate_disabled(const MDBX_env *env) {
+  return env->incore && (globals.runtime_flags & MDBX_DBG_NOFALLOC_INCORE) != 0;
+}
+
 /*----------------------------------------------------------------------------*/
 /* Cache coherence and mmap invalidation */
 #ifndef MDBX_CPU_WRITEBACK_INCOHERENT

src/dxb.c

@@ -154,6 +154,8 @@ __cold int dxb_resize(MDBX_env *const env, const pgno_t used_pgno, const pgno_t
   unsigned mresize_flags = env->flags & (MDBX_RDONLY | MDBX_WRITEMAP | MDBX_UTTERLY_NOSYNC);
   if (mode >= impilict_shrink)
     mresize_flags |= txn_shrink_allowed;
+  if (fallocate_disabled(env))
+    mresize_flags |= MDBX_MRESIZE_NO_FALLOC;
 
   if (limit_bytes == env->dxb_mmap.limit && size_bytes == env->dxb_mmap.current && size_bytes == env->dxb_mmap.filesize)
     goto bailout;
@@ -532,7 +534,8 @@ __cold int dxb_setup(MDBX_env *env, const int lck_rc, const mdbx_mode_t mode_bit
     if (unlikely(err != MDBX_SUCCESS))
       return err;
 
-    err = osal_fallocate(env->lazy_fd, env->dxb_mmap.filesize = env->dxb_mmap.current = env->geo_in_bytes.now);
+    err = (fallocate_disabled(env) ? osal_ftruncate : osal_fallocate)(
+        env->lazy_fd, env->dxb_mmap.filesize = env->dxb_mmap.current = env->geo_in_bytes.now);
     if (unlikely(err != MDBX_SUCCESS))
       return err;
 
@@ -681,7 +684,10 @@ __cold int dxb_setup(MDBX_env *env, const int lck_rc, const mdbx_mode_t mode_bit
       !(env->flags & MDBX_NORDAHEAD) && mdbx_is_readahead_reasonable(used_bytes, 0) == MDBX_RESULT_TRUE;
 
   err = osal_mmap(env->flags, &env->dxb_mmap, env->geo_in_bytes.now, env->geo_in_bytes.upper,
-                  (lck_rc && env->stuck_meta < 0) ? MMAP_OPTION_SETLENGTH : 0, env->pathname.dxb);
+                  (lck_rc && env->stuck_meta < 0)
+                      ? (fallocate_disabled(env) ? MMAP_OPTION_SETLENGTH | MMAP_OPTION_NOFALLOC : MMAP_OPTION_SETLENGTH)
+                      : 0,
+                  env->pathname.dxb);
   if (unlikely(err != MDBX_SUCCESS))
     return err;
 

src/osal.c

@@ -2087,7 +2087,7 @@ int osal_mmap(const int flags, osal_mmap_t *map, size_t size, const size_t limit
     return err;
 
   if ((flags & MDBX_RDONLY) == 0 && (options & MMAP_OPTION_SETLENGTH) != 0) {
-    err = osal_fallocate(map->fd, size);
+    err = ((options & MMAP_OPTION_NOFALLOC) ? osal_ftruncate : osal_fallocate)(map->fd, size);
     VERBOSE("ftruncate %zu, err %d", size, err);
     if (err != MDBX_SUCCESS)
       return err;
@@ -2333,7 +2333,7 @@ retry_file_and_section:
   }
 
   if ((flags & MDBX_RDONLY) == 0 && map->filesize != size) {
-    err = osal_fallocate(map->fd, size);
+    err = ((flags & MDBX_MRESIZE_NO_FALLOC) ? osal_ftruncate : osal_fallocate)(map->fd, size);
     if (err == MDBX_SUCCESS)
       map->filesize = size;
     /* ignore error, because Windows unable shrink file
@@ -2413,7 +2413,7 @@ retry_mapview:;
   } else {
     if (map->filesize != size) {
       if (size > map->filesize) {
-        rc = osal_fallocate(map->fd, size);
+        rc = ((flags & MDBX_MRESIZE_NO_FALLOC) ? osal_ftruncate : osal_fallocate)(map->fd, size);
         VERBOSE("f%s-%s %zu, err %d", "allocate", "extend", size, rc);
       } else if (flags & txn_shrink_allowed) {
         rc = osal_ftruncate(map->fd, size);

src/osal.h

@@ -481,11 +481,14 @@ MDBX_INTERNAL int osal_lockfile(mdbx_filehandle_t fd, bool wait);
 
 #define MMAP_OPTION_SETLENGTH 1
 #define MMAP_OPTION_SEMAPHORE 2
+#define MMAP_OPTION_NOFALLOC 4
 MDBX_INTERNAL int osal_mmap(const int flags, osal_mmap_t *map, size_t size, const size_t limit, const unsigned options,
                             const pathchar_t *pathname4logging);
 MDBX_INTERNAL int osal_munmap(osal_mmap_t *map);
+
 #define MDBX_MRESIZE_MAY_MOVE 0x00000100
 #define MDBX_MRESIZE_MAY_UNMAP 0x00000200
+#define MDBX_MRESIZE_NO_FALLOC 0x00000400
 MDBX_INTERNAL int osal_mresize(const int flags, osal_mmap_t *map, size_t size, size_t limit);
 #if defined(_WIN32) || defined(_WIN64)
 typedef struct {