new file mode 100644
--- /dev/null
+++ b/src/http/modules/ngx_http_degradation_module.c
@@ -0,0 +1,223 @@
+
+/*
+ * Copyright (C) Igor Sysoev
+ */
+
+
+#include <ngx_config.h>
+#include <ngx_core.h>
+#include <ngx_http.h>
+
+
+typedef struct {
+    size_t      sbrk_size;
+} ngx_http_degradation_main_conf_t;
+
+
+typedef struct {
+    ngx_uint_t  degrade;
+} ngx_http_degradation_loc_conf_t;
+
+
+static ngx_conf_enum_t  ngx_http_degrade[] = {
+    { ngx_string("204"), 204 },
+    { ngx_string("444"), 444 },
+    { ngx_null_string, 0 }
+};
+
+
+static void *ngx_http_degradation_create_main_conf(ngx_conf_t *cf);
+static void *ngx_http_degradation_create_loc_conf(ngx_conf_t *cf);
+static char *ngx_http_degradation_merge_loc_conf(ngx_conf_t *cf, void *parent,
+    void *child);
+static char *ngx_http_degradation(ngx_conf_t *cf, ngx_command_t *cmd,
+    void *conf);
+static ngx_int_t ngx_http_degradation_init(ngx_conf_t *cf);
+
+
+static ngx_command_t  ngx_http_degradation_commands[] = {
+
+    { ngx_string("degradation"),
+      NGX_HTTP_MAIN_CONF|NGX_CONF_TAKE1,
+      ngx_http_degradation,
+      NGX_HTTP_MAIN_CONF_OFFSET,
+      0,
+      NULL },
+
+    { ngx_string("degrade"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
+      ngx_conf_set_enum_slot,
+      NGX_HTTP_LOC_CONF_OFFSET,
+      offsetof(ngx_http_degradation_loc_conf_t, degrade),
+      &ngx_http_degrade },
+
+      ngx_null_command
+};
+
+
+static ngx_http_module_t  ngx_http_degradation_module_ctx = {
+    NULL,                                  /* preconfiguration */
+    ngx_http_degradation_init,             /* postconfiguration */
+
+    ngx_http_degradation_create_main_conf, /* create main configuration */
+    NULL,                                  /* init main configuration */
+
+    NULL,                                  /* create server configuration */
+    NULL,                                  /* merge server configuration */
+
+    ngx_http_degradation_create_loc_conf,  /* create location configuration */
+    ngx_http_degradation_merge_loc_conf    /* merge location configuration */
+};
+
+
+ngx_module_t  ngx_http_degradation_module = {
+    NGX_MODULE_V1,
+    &ngx_http_degradation_module_ctx,      /* module context */
+    ngx_http_degradation_commands,         /* module directives */
+    NGX_HTTP_MODULE,                       /* module type */
+    NULL,                                  /* init master */
+    NULL,                                  /* init module */
+    NULL,                                  /* init process */
+    NULL,                                  /* init thread */
+    NULL,                                  /* exit thread */
+    NULL,                                  /* exit process */
+    NULL,                                  /* exit master */
+    NGX_MODULE_V1_PADDING
+};
+
+
+static ngx_int_t
+ngx_http_degradation_handler(ngx_http_request_t *r)
+{
+    time_t                             now;
+    static size_t                      sbrk_size;
+    static time_t                      sbrk_time;
+    ngx_http_degradation_loc_conf_t   *dlcf;
+    ngx_http_degradation_main_conf_t  *dmcf;
+
+    dlcf = ngx_http_get_module_loc_conf(r, ngx_http_degradation_module);
+
+    if (dlcf->degrade == 0) {
+        return NGX_DECLINED;
+    }
+
+    dmcf = ngx_http_get_module_main_conf(r, ngx_http_degradation_module);
+
+    if (dmcf->sbrk_size) {
+
+        now = ngx_time();
+
+        /* lock mutex */
+
+        if (now != sbrk_time) {
+
+            /*
+             * ELF/i386 is loaded at 0x08000000, 128M
+             * ELF/amd64 is loaded at 0x00400000, 4M
+             *
+             * use a function address to substract the loading address
+             */
+
+            sbrk_size = (size_t) sbrk(0) - ((uintptr_t) ngx_palloc & ~0x3FFFFF);
+            sbrk_time = now;
+        }
+
+        /* unlock mutex */
+
+        if (sbrk_size >= dmcf->sbrk_size) {
+            ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
+                           "degradation sbrk: %uz", sbrk_size);
+
+            return dlcf->degrade;
+        }
+    }
+
+    return NGX_DECLINED;
+}
+
+
+static void *
+ngx_http_degradation_create_main_conf(ngx_conf_t *cf)
+{
+    ngx_http_degradation_main_conf_t  *dmcf;
+
+    dmcf = ngx_pcalloc(cf->pool, sizeof(ngx_http_degradation_main_conf_t));
+    if (dmcf == NULL) {
+        return NULL;
+    }
+
+    return dmcf;
+}
+
+
+static void *
+ngx_http_degradation_create_loc_conf(ngx_conf_t *cf)
+{
+    ngx_http_degradation_loc_conf_t  *conf;
+
+    conf = ngx_palloc(cf->pool, sizeof(ngx_http_degradation_loc_conf_t));
+    if (conf == NULL) {
+        return NULL;
+    }
+
+    conf->degrade = NGX_CONF_UNSET_UINT;
+
+    return conf;
+}
+
+
+static char *
+ngx_http_degradation_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
+{
+    ngx_http_degradation_loc_conf_t  *prev = parent;
+    ngx_http_degradation_loc_conf_t  *conf = child;
+
+    ngx_conf_merge_uint_value(conf->degrade, prev->degrade, 0);
+
+    return NGX_CONF_OK;
+}
+
+
+static char *
+ngx_http_degradation(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
+{
+    ngx_http_degradation_main_conf_t  *dmcf = conf;
+
+    ngx_str_t  *value, s;
+
+    value = cf->args->elts;
+
+    if (ngx_strncmp(value[1].data, "sbrk=", 5) == 0) {
+
+        s.len = value[1].len - 5;
+        s.data = value[1].data + 5;
+
+        dmcf->sbrk_size = ngx_parse_size(&s);
+        if (dmcf->sbrk_size == (size_t) NGX_ERROR) {
+            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                               "invalid sbrk size \"%V\"", &value[1]);
+            return NGX_CONF_ERROR;
+        }
+    }
+
+    return NGX_CONF_OK;
+}
+
+
+static ngx_int_t
+ngx_http_degradation_init(ngx_conf_t *cf)
+{
+    ngx_http_handler_pt        *h;
+    ngx_http_core_main_conf_t  *cmcf;
+
+    cmcf = ngx_http_conf_get_module_main_conf(cf, ngx_http_core_module);
+
+    h = ngx_array_push(&cmcf->phases[NGX_HTTP_PREACCESS_PHASE].handlers);
+    if (h == NULL) {
+        return NGX_ERROR;
+    }
+
+    *h = ngx_http_degradation_handler;
+
+    return NGX_OK;
+}