add option to drop file caches before closing files

src/config.cpp

@@ -40,6 +40,7 @@ namespace mergerfs
       minfreespace(MINFREESPACE_DEFAULT),
       moveonenospc(false),
       direct_io(false),
+      dropcacheonclose(false),
       POLICYINIT(access),
       POLICYINIT(chmod),
       POLICYINIT(chown),

src/config.hpp

@@ -48,6 +48,7 @@ namespace mergerfs
     uint64_t                 minfreespace;
     bool                     moveonenospc;
     bool                     direct_io;
+    bool                     dropcacheonclose;
 
   public:
     const Policy  *policies[FuseFunc::Enum::END];

src/option_parser.cpp

@@ -120,13 +120,13 @@ parse_and_process_minfreespace(const std::string &value,
 
 static
 int
-parse_and_process_moveonenospc(const std::string &value,
-                               bool              &moveonenospc)
+parse_and_process_boolean(const std::string &value,
+                          bool              &boolean)
 {
   if(value == "false")
-    moveonenospc = false;
+    boolean = false;
   else if(value == "true")
-    moveonenospc = true;
+    boolean = true;
   else
     return 1;
 
@@ -169,7 +169,9 @@ parse_and_process_kv_arg(Config            &config,
       if(key == "minfreespace")
         rv = parse_and_process_minfreespace(value,config.minfreespace);
       else if(key == "moveonenospc")
-        rv = parse_and_process_moveonenospc(value,config.moveonenospc);
+        rv = parse_and_process_boolean(value,config.moveonenospc);
+      else if(key == "dropcacheonclose")
+        rv = parse_and_process_boolean(value,config.dropcacheonclose);
     }
 
   if(rv == -1)
@@ -246,20 +248,25 @@ usage(void)
     "mergerfs options:\n"
     "    <srcpaths>             ':' delimited list of directories. Supports\n"
     "                           shell globbing (must be escaped in shell)\n"
-    "    -o defaults            default FUSE options which seem to provide the\n"
+    "    -o defaults            Default FUSE options which seem to provide the\n"
     "                           best performance: atomic_o_trunc, auto_cache,\n"
     "                           big_writes, default_permissions, splice_read,\n"
     "                           splice_write, splice_move\n"
-    "    -o direct_io           bypass additional caching, increases write\n"
-    "                           speeds at the cost of reads\n"
-    "    -o use_ino             mergerfs will generate inode values rather than\n"
-    "                           autogenerated by libfuse\n"
-    "    -o minfreespace=<int>  minimum free space needed for certain policies:\n"
-    "                           default 4G\n"
+    "    -o func.<f>=<p>        Set function <f> to policy <p>\n"
+    "    -o category.<c>=<p>    Set functions in category <c> to <p>\n"
+    "    -o direct_io           Bypass additional caching, increases write\n"
+    "                           speeds at the cost of reads. Please read docs\n"
+    "                           for more details as there are tradeoffs.\n"
+    "    -o use_ino             Have mergerfs generate inode values rather than\n"
+    "                           autogenerated by libfuse. Suggested.\n"
+    "    -o minfreespace=<int>  minimum free space needed for certain policies.\n"
+    "                           default=4G\n"
     "    -o moveonenospc=<bool> try to move file to another drive when ENOSPC\n"
-    "                           on write: default false\n"
-    "    -o func.<f>=<p>        set function <f> to policy <p>\n"
-    "    -o category.<c>=<p>    set functions in category <c> to <p>\n"
+    "                           on write. default=false\n"
+    "    -o dropcacheonclose=<bool>\n"
+    "                           when a file is closed suggest to OS it drop\n"
+    "                           the file's cache. This is useful when direct_io\n"
+    "                           is disabled. default=false\n"
             << std::endl;
 }
 
@@ -267,7 +274,8 @@ static
 void
 version(void)
 {
-  std::cout << "mergerfs version: " << MERGERFS_VERSION
+  std::cout << "mergerfs version: "
+            << MERGERFS_VERSION
             << std::endl;
 }
 

src/release.cpp

@@ -18,14 +18,25 @@
 
 #include <string>
 
+#include "config.hpp"
 #include "errno.hpp"
 #include "fileinfo.hpp"
 #include "fs_base_close.hpp"
+#include "fs_fadvise.hpp"
 
 static
 int
-_release(FileInfo *fi)
+_release(FileInfo   *fi,
+         const bool  dropcacheonclose)
 {
+  // according to Feh of nocache calling it once doesn't always work
+  // https://github.com/Feh/nocache
+  if(dropcacheonclose)
+    {
+      fs::fadvise(fi->fd,0,0,POSIX_FADV_DONTNEED);
+      fs::fadvise(fi->fd,0,0,POSIX_FADV_DONTNEED);
+    }
+
   fs::close(fi->fd);
 
   delete fi;
@@ -41,9 +52,11 @@ namespace mergerfs
     release(const char     *fusepath,
             fuse_file_info *ffi)
     {
+      const fuse_context *fc     = fuse_get_context();
+      const Config       &config = Config::get(fc);
       FileInfo           *fi     = reinterpret_cast<FileInfo*>(ffi->fh);
 
-      return _release(fi);
+      return _release(fi,config.dropcacheonclose);
     }
   }
 }