From 957c99d86fead8a7a65916a413a322a53ef9972c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=9B=D0=B5=D0=BE=D0=BD=D0=B8=D0=B4=20=D0=AE=D1=80=D1=8C?=
 =?UTF-8?q?=D0=B5=D0=B2=20=28Leonid=20Yuriev=29?= <leo@yuriev.ru>
Date: Mon, 12 Dec 2022 15:23:47 +0300
Subject: [PATCH] =?UTF-8?q?mdbx:=20=D0=B4=D0=BE=D0=B1=D0=B0=D0=B2=D0=BB?=
 =?UTF-8?q?=D0=B5=D0=BD=D0=B8=D0=B5=20`MDBX=5Fopt=5Fprefault=5Fwrite=5Fena?=
 =?UTF-8?q?ble`=20=D0=B2=D0=BC=D0=B5=D1=81=D1=82=D0=BE=20`MDBX=5FENABLE=5F?=
 =?UTF-8?q?PREFAULT`.?=
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---
 mdbx.h        |  5 +++++
 src/core.c    | 19 ++++++++++++++++---
 src/options.h | 12 ------------
 3 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/mdbx.h b/mdbx.h
index cb14bf33..1b3dcfd8 100644
--- a/mdbx.h
+++ b/mdbx.h
@@ -2254,6 +2254,11 @@ enum MDBX_option_t {
    * On Windows a write-through is used always but \ref MDBX_NOMETASYNC could
    * be used for switching to write-and-flush. */
   MDBX_opt_writethrough_threshold,
+
+  /** \brief Controls prevention of page-faults of reclaimed and allocated pages
+   * in the \ref MDBX_WRITEMAP mode by clearing ones through file handle before
+   * touching. */
+  MDBX_opt_prefault_write_enable,
 };
 #ifndef __cplusplus
 /** \ingroup c_settings */
diff --git a/src/core.c b/src/core.c
index 74922f9d..544e5934 100644
--- a/src/core.c
+++ b/src/core.c
@@ -7043,7 +7043,6 @@ static __inline pgr_t page_alloc_finalize(MDBX_env *const env,
     MDBX_ASAN_UNPOISON_MEMORY_REGION(ret.page, pgno2bytes(env, num));
     VALGRIND_MAKE_MEM_UNDEFINED(ret.page, pgno2bytes(env, num));
 
-#if MDBX_ENABLE_PREFAULT
     /* Содержимое выделенной страницы не нужно, но если страница отсутствует
      * в ОЗУ (что весьма вероятно), то любое обращение к ней приведет
      * к page-fault:
@@ -7107,7 +7106,6 @@ static __inline pgr_t page_alloc_finalize(MDBX_env *const env,
           need_clean = false;
       }
     }
-#endif /* MDBX_ENABLE_PREFAULT */
   } else {
     ret.page = page_malloc(txn, num);
     if (unlikely(!ret.page)) {
@@ -24553,6 +24551,18 @@ __cold int mdbx_env_set_option(MDBX_env *env, const MDBX_option_t option,
 #endif
     break;
 
+  case MDBX_opt_prefault_write_enable:
+    if (value == /* default */ UINT64_MAX) {
+      env->me_options.prefault_write = default_prefault_write(env);
+      env->me_options.flags.non_auto.prefault_write = false;
+    } else if (value > 1)
+      err = MDBX_EINVAL;
+    else {
+      env->me_options.prefault_write = value != 0;
+      env->me_options.flags.non_auto.prefault_write = true;
+    }
+    break;
+
   default:
     return MDBX_EINVAL;
   }
@@ -24634,6 +24644,10 @@ __cold int mdbx_env_get_option(const MDBX_env *env, const MDBX_option_t option,
 #endif
     break;
 
+  case MDBX_opt_prefault_write_enable:
+    *pvalue = env->me_options.prefault_write;
+    break;
+
   default:
     return MDBX_EINVAL;
   }
@@ -25120,7 +25134,6 @@ __dll_export
     " MDBX_AVOID_MSYNC=" MDBX_STRINGIFY(MDBX_AVOID_MSYNC)
     " MDBX_ENABLE_REFUND=" MDBX_STRINGIFY(MDBX_ENABLE_REFUND)
     " MDBX_ENABLE_MADVISE=" MDBX_STRINGIFY(MDBX_ENABLE_MADVISE)
-    " MDBX_ENABLE_PREFAULT=" MDBX_STRINGIFY(MDBX_ENABLE_PREFAULT)
     " MDBX_ENABLE_MINCORE=" MDBX_STRINGIFY(MDBX_ENABLE_MINCORE)
     " MDBX_ENABLE_PGOP_STAT=" MDBX_STRINGIFY(MDBX_ENABLE_PGOP_STAT)
     " MDBX_ENABLE_PROFGC=" MDBX_STRINGIFY(MDBX_ENABLE_PROFGC)
diff --git a/src/options.h b/src/options.h
index 3e9c9243..92b0f56e 100644
--- a/src/options.h
+++ b/src/options.h
@@ -87,18 +87,6 @@
 #error MDBX_ENABLE_PGOP_STAT must be defined as 0 or 1
 #endif /* MDBX_ENABLE_PGOP_STAT */
 
-/** Controls prevention of page-faults of reclaimed and allocated pages in the
- *  MDBX_WRITEMAP mode by clearing ones through file handle before touching. */
-#ifndef MDBX_ENABLE_PREFAULT
-#if MDBX_MMAP_INCOHERENT_FILE_WRITE
-#define MDBX_ENABLE_PREFAULT 0
-#else
-#define MDBX_ENABLE_PREFAULT 1
-#endif
-#elif !(MDBX_ENABLE_PREFAULT == 0 || MDBX_ENABLE_PREFAULT == 1)
-#error MDBX_ENABLE_PREFAULT must be defined as 0 or 1
-#endif /* MDBX_ENABLE_PREFAULT */
-
 /** Controls using Unix' mincore() to determine whether DB-pages
  * are resident in memory. */
 #ifndef MDBX_ENABLE_MINCORE