Cache: introduced min_free cache clearing.

Clearing cache based on free space left on a file system is
expected to allow better disk utilization in some cases, notably
when disk space might be also used for something other than nginx
cache (including nginx own temporary files) and while loading
cache (when cache size might be inaccurate for a while, effectively
disabling max_size cache clearing).

Based on a patch by Adam Bambuch.

src/http/ngx_http_cache.h

@@ -160,6 +160,7 @@ struct ngx_http_file_cache_s {
 
     ngx_path_t                      *path;
 
+    off_t                            min_free;
     off_t                            max_size;
     size_t                           bsize;
 

src/http/ngx_http_file_cache.c

@@ -1959,7 +1959,7 @@ ngx_http_file_cache_manager(void *data)
 {
     ngx_http_file_cache_t  *cache = data;
 
-    off_t       size;
+    off_t       size, free;
     time_t      wait;
     ngx_msec_t  elapsed, next;
     ngx_uint_t  count, watermark;
@@ -1988,7 +1988,19 @@ ngx_http_file_cache_manager(void *data)
                        size, count, (ngx_int_t) watermark);
 
         if (size < cache->max_size && count < watermark) {
-            break;
+
+            if (!cache->min_free) {
+                break;
+            }
+
+            free = ngx_fs_available(cache->path->name.data);
+
+            ngx_log_debug1(NGX_LOG_DEBUG_HTTP, ngx_cycle->log, 0,
+                           "http file cache free: %O", free);
+
+            if (free > cache->min_free) {
+                break;
+            }
         }
 
         wait = ngx_http_file_cache_forced_expire(cache);
@@ -2304,7 +2316,7 @@ ngx_http_file_cache_set_slot(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
 {
     char  *confp = conf;
 
-    off_t                   max_size;
+    off_t                   max_size, min_free;
     u_char                 *last, *p;
     time_t                  inactive;
     ssize_t                 size;
@@ -2341,6 +2353,7 @@ ngx_http_file_cache_set_slot(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
     name.len = 0;
     size = 0;
     max_size = NGX_MAX_OFF_T_VALUE;
+    min_free = 0;
 
     value = cf->args->elts;
 
@@ -2476,6 +2489,29 @@ ngx_http_file_cache_set_slot(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
             continue;
         }
 
+        if (ngx_strncmp(value[i].data, "min_free=", 9) == 0) {
+
+#if (NGX_WIN32 || NGX_HAVE_STATFS || NGX_HAVE_STATVFS)
+
+            s.len = value[i].len - 9;
+            s.data = value[i].data + 9;
+
+            min_free = ngx_parse_offset(&s);
+            if (min_free < 0) {
+                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
+                                   "invalid min_free value \"%V\"", &value[i]);
+                return NGX_CONF_ERROR;
+            }
+
+#else
+            ngx_conf_log_error(NGX_LOG_WARN, cf, 0,
+                               "min_free is not supported "
+                               "on this platform, ignored");
+#endif
+
+            continue;
+        }
+
         if (ngx_strncmp(value[i].data, "loader_files=", 13) == 0) {
 
             loader_files = ngx_atoi(value[i].data + 13, value[i].len - 13);
@@ -2607,6 +2643,7 @@ ngx_http_file_cache_set_slot(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
 
     cache->inactive = inactive;
     cache->max_size = max_size;
+    cache->min_free = min_free;
 
     caches = (ngx_array_t *) (confp + cmd->offset);
 

src/os/unix/ngx_files.c

@@ -884,6 +884,19 @@ ngx_fs_bsize(u_char *name)
     return (size_t) fs.f_bsize;
 }
 
+
+off_t
+ngx_fs_available(u_char *name)
+{
+    struct statfs  fs;
+
+    if (statfs((char *) name, &fs) == -1) {
+        return NGX_MAX_OFF_T_VALUE;
+    }
+
+    return (off_t) fs.f_bavail * fs.f_bsize;
+}
+
 #elif (NGX_HAVE_STATVFS)
 
 size_t
@@ -908,6 +921,19 @@ ngx_fs_bsize(u_char *name)
     return (size_t) fs.f_frsize;
 }
 
+
+off_t
+ngx_fs_available(u_char *name)
+{
+    struct statvfs  fs;
+
+    if (statvfs((char *) name, &fs) == -1) {
+        return NGX_MAX_OFF_T_VALUE;
+    }
+
+    return (off_t) fs.f_bavail * fs.f_frsize;
+}
+
 #else
 
 size_t
@@ -916,4 +942,11 @@ ngx_fs_bsize(u_char *name)
     return 512;
 }
 
+
+off_t
+ngx_fs_available(u_char *name)
+{
+    return NGX_MAX_OFF_T_VALUE;
+}
+
 #endif

src/os/unix/ngx_files.h

@@ -349,6 +349,7 @@ ngx_int_t ngx_directio_off(ngx_fd_t fd);
 #endif
 
 size_t ngx_fs_bsize(u_char *name);
+off_t ngx_fs_available(u_char *name);
 
 
 #if (NGX_HAVE_OPENAT)

src/os/win32/ngx_files.c

@@ -658,6 +658,19 @@ ngx_fs_bsize(u_char *name)
 }
 
 
+off_t
+ngx_fs_available(u_char *name)
+{
+    ULARGE_INTEGER  navail;
+
+    if (GetDiskFreeSpaceEx((const char *) name, &navail, NULL, NULL) == 0) {
+        return NGX_MAX_OFF_T_VALUE;
+    }
+
+    return (off_t) navail.QuadPart;
+}
+
+
 static ngx_int_t
 ngx_win32_check_filename(u_char *name, u_short *u, size_t len)
 {

src/os/win32/ngx_files.h

@@ -259,6 +259,7 @@ ngx_int_t ngx_directio_off(ngx_fd_t fd);
 #define ngx_directio_off_n          "ngx_directio_off_n"
 
 size_t ngx_fs_bsize(u_char *name);
+off_t ngx_fs_available(u_char *name);
 
 
 #define ngx_stdout               GetStdHandle(STD_OUTPUT_HANDLE)