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
  20 /* Cache priming module.
  21  *
  22  * The purpose of this module is to do RAID stripe width reads to prime the
  23  * buffer cache to do zero-copy I/O for subsequent sendfile calls. The idea is
  24  * to do a single large read at the start of the file to make sure that most or
  25  * all of the file is pulled into the buffer cache. Subsequent I/Os have
  26  * reduced latency.
  27  *
  28  * Tunables.
  29  *
  30  *      cacheprime:rsize    Amount of readahead in bytes. This should be a
  31  *                          multiple of the RAID stripe width.
  32  *      cacheprime:debug    Debug level at which to emit messages.
  33  */
  34
  35 #define READAHEAD_MIN       (128 * 1024)        /* min is 128 KiB */
  36 #define READAHEAD_MAX       (100 * 1024 * 1024) /* max is 100 MiB */
  37
  38 #define MODULE "cacheprime"
  39
  40 static int module_debug;
  41 static ssize_t g_readsz = 0;
  42 static void * g_readbuf = NULL;
  43
  44 /* Prime the kernel buffer cache with data from the specified file. We use
  45  * per-fsp data to make sure we only ever do this once. If pread is being
  46  * emulated by seek/read/seek, when this will suck quite a lot.
  47  */
  48 static bool prime_cache(
  49             struct vfs_handle_struct *  handle,
  50                         files_struct *                  fsp,
  51                         SMB_OFF_T                           offset,
  52                         size_t                              count)
  53 {
  54         SMB_OFF_T * last;
  55         ssize_t nread;
  56
  57         last = (SMB_OFF_T *)VFS_ADD_FSP_EXTENSION(handle, fsp, SMB_OFF_T, NULL);
  58         if (!last) {
  59                 return False;
  60         }
  61
  62         if (*last == -1) {
  63             /* Readahead disabled. */
  64             return False;
  65         }
  66
  67         if ((*last + g_readsz) > (offset + count)) {
  68             /* Skip readahead ... we've already been here. */
  69             return False;
  70         }
  71
  72         DEBUG(module_debug,
  73             ("%s: doing readahead of %lld bytes at %lld for %s\n",
  74             MODULE, (long long)g_readsz, (long long)*last,
  75             fsp_str_dbg(fsp)));
  76
  77         nread = sys_pread(fsp->fh->fd, g_readbuf, g_readsz, *last);
  78         if (nread < 0) {
  79             *last = -1;
  80             return False;
  81         }
  82
  83         *last += nread;
  84         return True;
  85 }
  86
  87 static int cprime_connect(
  88                 struct vfs_handle_struct *  handle,
  89                 const char *                service,
  90                 const char *                user)
  91 {
  92         int ret;
  93
  94         module_debug = lp_parm_int(SNUM(handle->conn), MODULE, "debug", 100);
  95         if (g_readbuf) {
  96                 /* Only allocate g_readbuf once. If the config changes and
  97                  * another client multiplexes onto this smbd, we don't want
  98                  * to risk memory corruption.
  99                  */
 100                 return SMB_VFS_NEXT_CONNECT(handle, service, user);
 101         }
 102
 103         ret = SMB_VFS_NEXT_CONNECT(handle, service, user);
 104         if (ret < 0) {
 105                 return ret;
 106         }
 107
 108         g_readsz = conv_str_size(lp_parm_const_string(SNUM(handle->conn),
 109                                         MODULE, "rsize", NULL));
 110
 111         if (g_readsz < READAHEAD_MIN) {
 112                 DEBUG(module_debug, ("%s: %ld bytes of readahead "
 113                             "requested, using minimum of %u\n",
 114                             MODULE, (long)g_readsz, READAHEAD_MIN));
 115                 g_readsz = READAHEAD_MIN;
 116         } else if (g_readsz > READAHEAD_MAX) {
 117                 DEBUG(module_debug, ("%s: %ld bytes of readahead "
 118                             "requested, using maximum of %u\n",
 119                             MODULE, (long)g_readsz, READAHEAD_MAX));
 120                 g_readsz = READAHEAD_MAX;
 121         }
 122
 123         if ((g_readbuf = SMB_MALLOC(g_readsz)) == NULL) {
 124                 /* Turn off readahead if we can't get a buffer. */
 125                 g_readsz = 0;
 126         }
 127
 128         return 0;
 129 }
 130
 131 static ssize_t cprime_sendfile(
 132                 struct vfs_handle_struct *  handle,
 133                 int                         tofd,
 134                 files_struct *              fromfsp,
 135                 const DATA_BLOB *           header,
 136                 SMB_OFF_T                   offset,
 137                 size_t                      count)
 138 {
 139         if (g_readbuf && offset == 0) {
 140                 prime_cache(handle, fromfsp, offset, count);
 141         }
 142
 143         return SMB_VFS_NEXT_SENDFILE(handle, tofd, fromfsp,
 144                                      header, offset, count);
 145 }
 146
 147 static ssize_t cprime_read(
 148                 vfs_handle_struct * handle,
 149                 files_struct *      fsp,
 150                 void *              data,
 151                 size_t              count)
 152 {
 153         SMB_OFF_T offset;
 154
 155         offset = SMB_VFS_LSEEK(fsp, 0, SEEK_CUR);
 156         if (offset >= 0 && g_readbuf)  {
 157                 prime_cache(handle, fsp, offset, count);
 158                 SMB_VFS_LSEEK(fsp, offset, SEEK_SET);
 159         }
 160
 161         return SMB_VFS_NEXT_READ(handle, fsp, data, count);
 162 }
 163
 164 static ssize_t cprime_pread(
 165                 vfs_handle_struct * handle,
 166                 files_struct *      fsp,
 167                 void *              data,
 168                         size_t              count,
 169                 SMB_OFF_T           offset)
 170 {
 171         if (g_readbuf) {
 172                 prime_cache(handle, fsp, offset, count);
 173         }
 174
 175         return SMB_VFS_NEXT_PREAD(handle, fsp, data, count, offset);
 176 }
 177
 178 static struct vfs_fn_pointers vfs_cacheprime_fns = {
 179         .sendfile = cprime_sendfile,
 180         .pread = cprime_pread,
 181         .vfs_read = cprime_read,
 182         .connect_fn = cprime_connect,
 183 };
 184
 185 /* -------------------------------------------------------------------------
 186  * Samba module initialisation entry point.
 187  * -------------------------------------------------------------------------
 188  */
 189
 190 NTSTATUS vfs_cacheprime_init(void);
 191 NTSTATUS vfs_cacheprime_init(void)
 192 {
 193         return smb_register_vfs(SMB_VFS_INTERFACE_VERSION, MODULE,
 194                                 &vfs_cacheprime_fns);
 195 }
 196
 197 /* vim: set sw=4 ts=4 tw=79 et: */