1 /* $NetBSD: uvm_readahead.c,v 1.6 2009/06/10 01:54:08 yamt Exp $ */ 2 3 /*- 4 * Copyright (c)2003, 2005, 2009 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 1.6 2009/06/10 01:54:08 yamt 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 struct pool_cache ractx_cache; 87 88 /* 89 * uvm_ra_init: initialize readahead module. 90 */ 91 92 void 93 uvm_ra_init(void) 94 { 95 96 pool_cache_bootstrap(&ractx_cache, sizeof(struct uvm_ractx), 0, 0, 0, 97 "ractx", NULL, IPL_NONE, NULL, NULL, NULL); 98 } 99 100 static struct uvm_ractx * 101 ra_allocctx(void) 102 { 103 104 return pool_cache_get(&ractx_cache, PR_NOWAIT); 105 } 106 107 static void 108 ra_freectx(struct uvm_ractx *ra) 109 { 110 111 pool_cache_put(&ractx_cache, ra); 112 } 113 114 /* 115 * ra_startio: start i/o for read-ahead. 116 * 117 * => start i/o for each RA_IOCHUNK sized chunk. 118 * => return offset to which we started i/o. 119 */ 120 121 static off_t 122 ra_startio(struct uvm_object *uobj, off_t off, size_t sz) 123 { 124 const off_t endoff = off + sz; 125 126 DPRINTF(("%s: uobj=%p, off=%" PRIu64 ", endoff=%" PRIu64 "\n", 127 __func__, uobj, off, endoff)); 128 off = trunc_page(off); 129 while (off < endoff) { 130 const size_t chunksize = RA_IOCHUNK; 131 int error; 132 size_t donebytes; 133 int npages; 134 int orignpages; 135 size_t bytelen; 136 137 KASSERT((chunksize & (chunksize - 1)) == 0); 138 KASSERT((off & PAGE_MASK) == 0); 139 bytelen = ((off + chunksize) & -(off_t)chunksize) - off; 140 KASSERT((bytelen & PAGE_MASK) == 0); 141 npages = orignpages = bytelen >> PAGE_SHIFT; 142 KASSERT(npages != 0); 143 144 /* 145 * use UVM_ADV_RANDOM to avoid recursion. 146 */ 147 148 mutex_enter(&uobj->vmobjlock); 149 error = (*uobj->pgops->pgo_get)(uobj, off, NULL, 150 &npages, 0, VM_PROT_READ, UVM_ADV_RANDOM, 0); 151 DPRINTF(("%s: off=%" PRIu64 ", bytelen=%zu -> %d\n", 152 __func__, off, bytelen, error)); 153 if (error != 0 && error != EBUSY) { 154 if (error != EINVAL) { /* maybe past EOF */ 155 DPRINTF(("%s: error=%d\n", __func__, error)); 156 } 157 break; 158 } 159 KASSERT(orignpages == npages); 160 donebytes = orignpages << PAGE_SHIFT; 161 off += donebytes; 162 } 163 164 return off; 165 } 166 167 /* ------------------------------------------------------------ */ 168 169 /* 170 * uvm_ra_allocctx: allocate a context. 171 */ 172 173 struct uvm_ractx * 174 uvm_ra_allocctx(void) 175 { 176 struct uvm_ractx *ra; 177 178 ra = ra_allocctx(); 179 if (ra != NULL) { 180 ra->ra_flags = 0; 181 } 182 183 return ra; 184 } 185 186 /* 187 * uvm_ra_freectx: free a context. 188 */ 189 190 void 191 uvm_ra_freectx(struct uvm_ractx *ra) 192 { 193 194 KASSERT(ra != NULL); 195 ra_freectx(ra); 196 } 197 198 /* 199 * uvm_ra_request: update a read-ahead context and start i/o if appropriate. 200 * 201 * => called when [reqoff, reqoff+reqsize) is requested. 202 * => object must be locked by caller, will return locked. 203 */ 204 205 void 206 uvm_ra_request(struct uvm_ractx *ra, int advice, struct uvm_object *uobj, 207 off_t reqoff, size_t reqsize) 208 { 209 210 KASSERT(mutex_owned(&uobj->vmobjlock)); 211 212 if (ra == NULL || advice == UVM_ADV_RANDOM) { 213 return; 214 } 215 216 if (advice == UVM_ADV_SEQUENTIAL) { 217 218 /* 219 * always do read-ahead with a large window. 220 */ 221 222 if ((ra->ra_flags & RA_VALID) == 0) { 223 ra->ra_winstart = ra->ra_next = 0; 224 ra->ra_flags |= RA_VALID; 225 } 226 if (reqoff < ra->ra_winstart) { 227 ra->ra_next = reqoff; 228 } 229 ra->ra_winsize = RA_WINSIZE_SEQENTIAL; 230 goto do_readahead; 231 } 232 233 /* 234 * a request with UVM_ADV_NORMAL hint. (ie. no hint) 235 * 236 * we keep a sliding window in order to determine: 237 * - if the previous read-ahead was successful or not. 238 * - how many bytes to read-ahead. 239 */ 240 241 /* 242 * if it's the first request for this context, 243 * initialize context and return. 244 */ 245 246 if ((ra->ra_flags & RA_VALID) == 0) { 247 initialize: 248 ra->ra_winstart = ra->ra_next = reqoff + reqsize; 249 ra->ra_winsize = RA_WINSIZE_INIT; 250 ra->ra_flags |= RA_VALID; 251 goto done; 252 } 253 254 /* 255 * if it isn't in our window, 256 * initialize context and return. 257 * (read-ahead miss) 258 */ 259 260 if (reqoff < ra->ra_winstart || 261 ra->ra_winstart + ra->ra_winsize < reqoff) { 262 263 /* 264 * ... unless we seem to be reading the same chunk repeatedly. 265 * 266 * XXX should have some margin? 267 */ 268 269 if (reqoff + reqsize == ra->ra_winstart) { 270 DPRINTF(("%s: %p: same block: off=%" PRIu64 271 ", size=%zd, winstart=%" PRIu64 "\n", 272 __func__, ra, reqoff, reqsize, ra->ra_winstart)); 273 goto done; 274 } 275 goto initialize; 276 } 277 278 /* 279 * it's in our window. (read-ahead hit) 280 * - start read-ahead i/o if appropriate. 281 * - advance and enlarge window. 282 */ 283 284 do_readahead: 285 286 /* 287 * don't bother to read-ahead behind current request. 288 */ 289 290 if (reqoff > ra->ra_next) { 291 ra->ra_next = reqoff; 292 } 293 294 /* 295 * try to make [reqoff, reqoff+ra_winsize) in-core. 296 * note that [reqoff, ra_next) is considered already done. 297 */ 298 299 if (reqoff + ra->ra_winsize > ra->ra_next) { 300 off_t raoff = MAX(reqoff, ra->ra_next); 301 size_t rasize = reqoff + ra->ra_winsize - ra->ra_next; 302 303 #if defined(DIAGNOSTIC) 304 if (rasize > RA_WINSIZE_MAX) { 305 printf("%s: corrupted context", __func__); 306 rasize = RA_WINSIZE_MAX; 307 } 308 #endif /* defined(DIAGNOSTIC) */ 309 310 /* 311 * issue read-ahead only if we can start big enough i/o. 312 * otherwise we end up with a stream of small i/o. 313 */ 314 315 if (rasize >= RA_MINSIZE) { 316 off_t next; 317 318 mutex_exit(&uobj->vmobjlock); 319 next = ra_startio(uobj, raoff, rasize); 320 mutex_enter(&uobj->vmobjlock); 321 ra->ra_next = next; 322 } 323 } 324 325 /* 326 * update window. 327 * 328 * enlarge window by reqsize, so that it grows in a predictable manner 329 * regardless of the size of each read(2). 330 */ 331 332 ra->ra_winstart = reqoff + reqsize; 333 ra->ra_winsize = MIN(RA_WINSIZE_MAX, ra->ra_winsize + reqsize); 334 335 done:; 336 } 337 338 int 339 uvm_readahead(struct uvm_object *uobj, off_t off, off_t size) 340 { 341 342 /* 343 * don't allow too much read-ahead. 344 */ 345 if (size > RA_WINSIZE_MAX) { 346 size = RA_WINSIZE_MAX; 347 } 348 ra_startio(uobj, off, size); 349 return 0; 350 } 351