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