1 /* $NetBSD: uvm_readahead.c,v 1.4 2007/05/11 12:11:09 tsutsui Exp $ */ 2 3 /*- 4 * Copyright (c)2003, 2005 YAMAMOTO Takashi, 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 */ 28 29 /* 30 * uvm_object read-ahead 31 * 32 * TODO: 33 * - tune. 34 * - handle multiple streams. 35 * - find a better way to deal with PGO_LOCKED pager requests. 36 * (currently just ignored) 37 * - consider the amount of memory in the system. 38 * - consider the speed of the underlying device. 39 * - consider filesystem block size / block layout. 40 */ 41 42 #include <sys/cdefs.h> 43 __KERNEL_RCSID(0, "$NetBSD: uvm_readahead.c,v 1.4 2007/05/11 12:11:09 tsutsui Exp $"); 44 45 #include <sys/param.h> 46 #include <sys/pool.h> 47 48 #include <uvm/uvm.h> 49 #include <uvm/uvm_readahead.h> 50 51 #if defined(READAHEAD_DEBUG) 52 #define DPRINTF(a) printf a 53 #else /* defined(READAHEAD_DEBUG) */ 54 #define DPRINTF(a) /* nothing */ 55 #endif /* defined(READAHEAD_DEBUG) */ 56 57 /* 58 * uvm_ractx: read-ahead context. 59 */ 60 61 struct uvm_ractx { 62 int ra_flags; 63 #define RA_VALID 1 64 off_t ra_winstart; /* window start offset */ 65 size_t ra_winsize; /* window size */ 66 off_t ra_next; /* next offset to read-ahead */ 67 }; 68 69 #if defined(sun2) || (defined(sun3) && defined(_SUN3_)) 70 /* XXX: on sun2 and sun3 (but not sun3x) MAXPHYS is 0xe000 */ 71 #undef MAXPHYS 72 #define MAXPHYS 0x8000 /* XXX */ 73 #endif 74 75 #define RA_WINSIZE_INIT MAXPHYS /* initial window size */ 76 #define RA_WINSIZE_MAX (MAXPHYS * 8) /* max window size */ 77 #define RA_WINSIZE_SEQENTIAL RA_WINSIZE_MAX /* fixed window size used for 78 SEQUENTIAL hint */ 79 #define RA_MINSIZE (MAXPHYS * 2) /* min size to start i/o */ 80 #define RA_IOCHUNK MAXPHYS /* read-ahead i/o chunk size */ 81 82 static off_t ra_startio(struct uvm_object *, off_t, size_t); 83 static struct uvm_ractx *ra_allocctx(void); 84 static void ra_freectx(struct uvm_ractx *); 85 86 static POOL_INIT(ractx_pool, sizeof(struct uvm_ractx), 0, 0, 0, "ractx", 87 &pool_allocator_nointr, IPL_NONE); 88 89 static struct uvm_ractx * 90 ra_allocctx(void) 91 { 92 93 return pool_get(&ractx_pool, PR_NOWAIT); 94 } 95 96 static void 97 ra_freectx(struct uvm_ractx *ra) 98 { 99 100 pool_put(&ractx_pool, ra); 101 } 102 103 /* 104 * ra_startio: start i/o for read-ahead. 105 * 106 * => start i/o for each RA_IOCHUNK sized chunk. 107 * => return offset to which we started i/o. 108 */ 109 110 static off_t 111 ra_startio(struct uvm_object *uobj, off_t off, size_t sz) 112 { 113 const off_t endoff = off + sz; 114 115 DPRINTF(("%s: uobj=%p, off=%" PRIu64 ", endoff=%" PRIu64 "\n", 116 __func__, uobj, off, endoff)); 117 off = trunc_page(off); 118 while (off < endoff) { 119 const size_t chunksize = RA_IOCHUNK; 120 int error; 121 size_t donebytes; 122 int npages; 123 int orignpages; 124 size_t bytelen; 125 126 KASSERT((chunksize & (chunksize - 1)) == 0); 127 KASSERT((off & PAGE_MASK) == 0); 128 bytelen = ((off + chunksize) & -(off_t)chunksize) - off; 129 KASSERT((bytelen & PAGE_MASK) == 0); 130 npages = orignpages = bytelen >> PAGE_SHIFT; 131 KASSERT(npages != 0); 132 133 /* 134 * use UVM_ADV_RANDOM to avoid recursion. 135 */ 136 137 simple_lock(&uobj->vmobjlock); 138 error = (*uobj->pgops->pgo_get)(uobj, off, NULL, 139 &npages, 0, VM_PROT_READ, UVM_ADV_RANDOM, 0); 140 DPRINTF(("%s: off=%" PRIu64 ", bytelen=%zu -> %d\n", 141 __func__, off, bytelen, error)); 142 if (error != 0 && error != EBUSY) { 143 if (error != EINVAL) { /* maybe past EOF */ 144 DPRINTF(("%s: error=%d\n", __func__, error)); 145 } 146 break; 147 } 148 KASSERT(orignpages == npages); 149 donebytes = orignpages << PAGE_SHIFT; 150 off += donebytes; 151 } 152 153 return off; 154 } 155 156 /* ------------------------------------------------------------ */ 157 158 /* 159 * uvm_ra_allocctx: allocate a context. 160 */ 161 162 struct uvm_ractx * 163 uvm_ra_allocctx(void) 164 { 165 struct uvm_ractx *ra; 166 167 ra = ra_allocctx(); 168 if (ra != NULL) { 169 ra->ra_flags = 0; 170 } 171 172 return ra; 173 } 174 175 /* 176 * uvm_ra_freectx: free a context. 177 */ 178 179 void 180 uvm_ra_freectx(struct uvm_ractx *ra) 181 { 182 183 KASSERT(ra != NULL); 184 ra_freectx(ra); 185 } 186 187 /* 188 * uvm_ra_request: update a read-ahead context and start i/o if appropriate. 189 * 190 * => called when [reqoff, reqoff+reqsize) is requested. 191 */ 192 193 void 194 uvm_ra_request(struct uvm_ractx *ra, int advice, struct uvm_object *uobj, 195 off_t reqoff, size_t reqsize) 196 { 197 198 if (ra == NULL || advice == UVM_ADV_RANDOM) { 199 return; 200 } 201 202 /* 203 * XXX needs locking? maybe. 204 * but the worst effect is merely a bad read-ahead. 205 */ 206 207 if (advice == UVM_ADV_SEQUENTIAL) { 208 209 /* 210 * always do read-ahead with a large window. 211 */ 212 213 if ((ra->ra_flags & RA_VALID) == 0) { 214 ra->ra_winstart = ra->ra_next = 0; 215 ra->ra_flags |= RA_VALID; 216 } 217 if (reqoff < ra->ra_winstart) { 218 ra->ra_next = reqoff; 219 } 220 ra->ra_winsize = RA_WINSIZE_SEQENTIAL; 221 goto do_readahead; 222 } 223 224 /* 225 * a request with UVM_ADV_NORMAL hint. (ie. no hint) 226 * 227 * we keep a sliding window in order to determine: 228 * - if the previous read-ahead was successful or not. 229 * - how many bytes to read-ahead. 230 */ 231 232 /* 233 * if it's the first request for this context, 234 * initialize context and return. 235 */ 236 237 if ((ra->ra_flags & RA_VALID) == 0) { 238 initialize: 239 ra->ra_winstart = ra->ra_next = reqoff + reqsize; 240 ra->ra_winsize = RA_WINSIZE_INIT; 241 ra->ra_flags |= RA_VALID; 242 goto done; 243 } 244 245 /* 246 * if it isn't in our window, 247 * initialize context and return. 248 * (read-ahead miss) 249 */ 250 251 if (reqoff < ra->ra_winstart || 252 ra->ra_winstart + ra->ra_winsize < reqoff) { 253 254 /* 255 * ... unless we seem to be reading the same chunk repeatedly. 256 * 257 * XXX should have some margin? 258 */ 259 260 if (reqoff + reqsize == ra->ra_winstart) { 261 DPRINTF(("%s: %p: same block: off=%" PRIu64 262 ", size=%zd, winstart=%" PRIu64 "\n", 263 __func__, ra, reqoff, reqsize, ra->ra_winstart)); 264 goto done; 265 } 266 goto initialize; 267 } 268 269 /* 270 * it's in our window. (read-ahead hit) 271 * - start read-ahead i/o if appropriate. 272 * - advance and enlarge window. 273 */ 274 275 do_readahead: 276 277 /* 278 * don't bother to read-ahead behind current request. 279 */ 280 281 if (reqoff > ra->ra_next) { 282 ra->ra_next = reqoff; 283 } 284 285 /* 286 * try to make [reqoff, reqoff+ra_winsize) in-core. 287 * note that [reqoff, ra_next) is considered already done. 288 */ 289 290 if (reqoff + ra->ra_winsize > ra->ra_next) { 291 off_t raoff = MAX(reqoff, ra->ra_next); 292 size_t rasize = reqoff + ra->ra_winsize - ra->ra_next; 293 294 #if defined(DIAGNOSTIC) 295 if (rasize > RA_WINSIZE_MAX) { 296 297 /* 298 * shouldn't happen as far as we're protected by 299 * kernel_lock. 300 */ 301 302 printf("%s: corrupted context", __func__); 303 rasize = RA_WINSIZE_MAX; 304 } 305 #endif /* defined(DIAGNOSTIC) */ 306 307 /* 308 * issue read-ahead only if we can start big enough i/o. 309 * otherwise we end up with a stream of small i/o. 310 */ 311 312 if (rasize >= RA_MINSIZE) { 313 ra->ra_next = ra_startio(uobj, raoff, rasize); 314 } 315 } 316 317 /* 318 * update window. 319 * 320 * enlarge window by reqsize, so that it grows in a predictable manner 321 * regardless of the size of each read(2). 322 */ 323 324 ra->ra_winstart = reqoff + reqsize; 325 ra->ra_winsize = MIN(RA_WINSIZE_MAX, ra->ra_winsize + reqsize); 326 327 done:; 328 } 329