source3/modules/vfs_cacheprime.c

   1 /*
   2  * Copyright (c) James Peach 2005-2006
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 3 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 #include "includes.h"
  19 #include "smbd/smbd.h"
  20 #include "lib/util/sys_rw.h"
  21
  22 /* Cache priming module.
  23  *
  24  * The purpose of this module is to do RAID stripe width reads to prime the
  25  * buffer cache to do zero-copy I/O for subsequent sendfile calls. The idea is
  26  * to do a single large read at the start of the file to make sure that most or
  27  * all of the file is pulled into the buffer cache. Subsequent I/Os have
  28  * reduced latency.
  29  *
  30  * Tunables.
  31  *
  32  *      cacheprime:rsize    Amount of readahead in bytes. This should be a
  33  *                          multiple of the RAID stripe width.
  34  *      cacheprime:debug    Debug level at which to emit messages.
  35  */
  36
  37 #define READAHEAD_MIN       (128 * 1024)        /* min is 128 KiB */
  38 #define READAHEAD_MAX       (100 * 1024 * 1024) /* max is 100 MiB */
  39
  40 #define MODULE "cacheprime"
  41
  42 static int module_debug;
  43 static ssize_t g_readsz = 0;
  44 static void * g_readbuf = NULL;
  45
  46 /* Prime the kernel buffer cache with data from the specified file. We use
  47  * per-fsp data to make sure we only ever do this once. If pread is being
  48  * emulated by seek/read/seek, when this will suck quite a lot.
  49  */
  50 static bool prime_cache(
  51             struct vfs_handle_struct *  handle,
  52                         files_struct *                  fsp,
  53                         off_t                       offset,
  54                         size_t                              count)
  55 {
  56         off_t * last;
  57         ssize_t nread;
  58
  59         last = VFS_ADD_FSP_EXTENSION(handle, fsp, off_t, NULL);
  60         if (!last) {
  61                 return False;
  62         }
  63
  64         if (*last == -1) {
  65             /* Readahead disabled. */
  66             return False;
  67         }
  68
  69         if ((*last + g_readsz) > (offset + count)) {
  70             /* Skip readahead ... we've already been here. */
  71             return False;
  72         }
  73
  74         DEBUG(module_debug,
  75             ("%s: doing readahead of %lld bytes at %lld for %s\n",
  76             MODULE, (long long)g_readsz, (long long)*last,
  77             fsp_str_dbg(fsp)));
  78
  79         nread = sys_pread(fsp->fh->fd, g_readbuf, g_readsz, *last);
  80         if (nread < 0) {
  81             *last = -1;
  82             return False;
  83         }
  84
  85         *last += nread;
  86         return True;
  87 }
  88
  89 static int cprime_connect(
  90                 struct vfs_handle_struct *  handle,
  91                 const char *                service,
  92                 const char *                user)
  93 {
  94         int ret;
  95
  96         module_debug = lp_parm_int(SNUM(handle->conn), MODULE, "debug", 100);
  97         if (g_readbuf) {
  98                 /* Only allocate g_readbuf once. If the config changes and
  99                  * another client multiplexes onto this smbd, we don't want
 100                  * to risk memory corruption.
 101                  */
 102                 return SMB_VFS_NEXT_CONNECT(handle, service, user);
 103         }
 104
 105         ret = SMB_VFS_NEXT_CONNECT(handle, service, user);
 106         if (ret < 0) {
 107                 return ret;
 108         }
 109
 110         g_readsz = conv_str_size(lp_parm_const_string(SNUM(handle->conn),
 111                                         MODULE, "rsize", NULL));
 112
 113         if (g_readsz < READAHEAD_MIN) {
 114                 DEBUG(module_debug, ("%s: %ld bytes of readahead "
 115                             "requested, using minimum of %u\n",
 116                             MODULE, (long)g_readsz, READAHEAD_MIN));
 117                 g_readsz = READAHEAD_MIN;
 118         } else if (g_readsz > READAHEAD_MAX) {
 119                 DEBUG(module_debug, ("%s: %ld bytes of readahead "
 120                             "requested, using maximum of %u\n",
 121                             MODULE, (long)g_readsz, READAHEAD_MAX));
 122                 g_readsz = READAHEAD_MAX;
 123         }
 124
 125         if ((g_readbuf = SMB_MALLOC(g_readsz)) == NULL) {
 126                 /* Turn off readahead if we can't get a buffer. */
 127                 g_readsz = 0;
 128         }
 129
 130         return 0;
 131 }
 132
 133 static ssize_t cprime_sendfile(
 134                 struct vfs_handle_struct *  handle,
 135                 int                         tofd,
 136                 files_struct *              fromfsp,
 137                 const DATA_BLOB *           header,
 138                 off_t                   offset,
 139                 size_t                      count)
 140 {
 141         if (g_readbuf && offset == 0) {
 142                 prime_cache(handle, fromfsp, offset, count);
 143         }
 144
 145         return SMB_VFS_NEXT_SENDFILE(handle, tofd, fromfsp,
 146                                      header, offset, count);
 147 }
 148
 149 static ssize_t cprime_pread(
 150                 vfs_handle_struct * handle,
 151                 files_struct *      fsp,
 152                 void *              data,
 153                         size_t              count,
 154                 off_t           offset)
 155 {
 156         if (g_readbuf) {
 157                 prime_cache(handle, fsp, offset, count);
 158         }
 159
 160         return SMB_VFS_NEXT_PREAD(handle, fsp, data, count, offset);
 161 }
 162
 163 static struct vfs_fn_pointers vfs_cacheprime_fns = {
 164     .sendfile_fn = cprime_sendfile,
 165     .pread_fn = cprime_pread,
 166     .connect_fn = cprime_connect,
 167 };
 168
 169 /* -------------------------------------------------------------------------
 170  * Samba module initialisation entry point.
 171  * -------------------------------------------------------------------------
 172  */
 173
 174 static_decl_vfs;
 175 NTSTATUS vfs_cacheprime_init(TALLOC_CTX *ctx)
 176 {
 177         return smb_register_vfs(SMB_VFS_INTERFACE_VERSION, MODULE,
 178                                 &vfs_cacheprime_fns);
 179 }
 180
 181 /* vim: set sw=4 ts=4 tw=79 et: */