/* $NetBSD: uvm_readahead.c,v 1.3 2007/03/12 18:18:39 ad Exp $ */ /*- * Copyright (c)2003, 2005 YAMAMOTO Takashi, * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ /* * uvm_object read-ahead * * TODO: * - tune. * - handle multiple streams. * - find a better way to deal with PGO_LOCKED pager requests. * (currently just ignored) * - consider the amount of memory in the system. * - consider the speed of the underlying device. * - consider filesystem block size / block layout. */ #include __KERNEL_RCSID(0, "$NetBSD: uvm_readahead.c,v 1.3 2007/03/12 18:18:39 ad Exp $"); #include #include #include #include #if defined(READAHEAD_DEBUG) #define DPRINTF(a) printf a #else /* defined(READAHEAD_DEBUG) */ #define DPRINTF(a) /* nothing */ #endif /* defined(READAHEAD_DEBUG) */ /* * uvm_ractx: read-ahead context. */ struct uvm_ractx { int ra_flags; #define RA_VALID 1 off_t ra_winstart; /* window start offset */ size_t ra_winsize; /* window size */ off_t ra_next; /* next offset to read-ahead */ }; #define RA_WINSIZE_INIT MAXPHYS /* initial window size */ #define RA_WINSIZE_MAX (MAXPHYS * 8) /* max window size */ #define RA_WINSIZE_SEQENTIAL RA_WINSIZE_MAX /* fixed window size used for SEQUENTIAL hint */ #define RA_MINSIZE (MAXPHYS * 2) /* min size to start i/o */ #define RA_IOCHUNK MAXPHYS /* read-ahead i/o chunk size */ static off_t ra_startio(struct uvm_object *, off_t, size_t); static struct uvm_ractx *ra_allocctx(void); static void ra_freectx(struct uvm_ractx *); static POOL_INIT(ractx_pool, sizeof(struct uvm_ractx), 0, 0, 0, "ractx", &pool_allocator_nointr, IPL_NONE); static struct uvm_ractx * ra_allocctx(void) { return pool_get(&ractx_pool, PR_NOWAIT); } static void ra_freectx(struct uvm_ractx *ra) { pool_put(&ractx_pool, ra); } /* * ra_startio: start i/o for read-ahead. * * => start i/o for each RA_IOCHUNK sized chunk. * => return offset to which we started i/o. */ static off_t ra_startio(struct uvm_object *uobj, off_t off, size_t sz) { const off_t endoff = off + sz; DPRINTF(("%s: uobj=%p, off=%" PRIu64 ", endoff=%" PRIu64 "\n", __func__, uobj, off, endoff)); off = trunc_page(off); while (off < endoff) { const size_t chunksize = RA_IOCHUNK; int error; size_t donebytes; int npages; int orignpages; size_t bytelen; KASSERT((chunksize & (chunksize - 1)) == 0); KASSERT((off & PAGE_MASK) == 0); bytelen = ((off + chunksize) & -(off_t)chunksize) - off; KASSERT((bytelen & PAGE_MASK) == 0); npages = orignpages = bytelen >> PAGE_SHIFT; KASSERT(npages != 0); /* * use UVM_ADV_RANDOM to avoid recursion. */ simple_lock(&uobj->vmobjlock); error = (*uobj->pgops->pgo_get)(uobj, off, NULL, &npages, 0, VM_PROT_READ, UVM_ADV_RANDOM, 0); DPRINTF(("%s: off=%" PRIu64 ", bytelen=%zu -> %d\n", __func__, off, bytelen, error)); if (error != 0 && error != EBUSY) { if (error != EINVAL) { /* maybe past EOF */ DPRINTF(("%s: error=%d\n", __func__, error)); } break; } KASSERT(orignpages == npages); donebytes = orignpages << PAGE_SHIFT; off += donebytes; } return off; } /* ------------------------------------------------------------ */ /* * uvm_ra_allocctx: allocate a context. */ struct uvm_ractx * uvm_ra_allocctx(void) { struct uvm_ractx *ra; ra = ra_allocctx(); if (ra != NULL) { ra->ra_flags = 0; } return ra; } /* * uvm_ra_freectx: free a context. */ void uvm_ra_freectx(struct uvm_ractx *ra) { KASSERT(ra != NULL); ra_freectx(ra); } /* * uvm_ra_request: update a read-ahead context and start i/o if appropriate. * * => called when [reqoff, reqoff+reqsize) is requested. */ void uvm_ra_request(struct uvm_ractx *ra, int advice, struct uvm_object *uobj, off_t reqoff, size_t reqsize) { if (ra == NULL || advice == UVM_ADV_RANDOM) { return; } /* * XXX needs locking? maybe. * but the worst effect is merely a bad read-ahead. */ if (advice == UVM_ADV_SEQUENTIAL) { /* * always do read-ahead with a large window. */ if ((ra->ra_flags & RA_VALID) == 0) { ra->ra_winstart = ra->ra_next = 0; ra->ra_flags |= RA_VALID; } if (reqoff < ra->ra_winstart) { ra->ra_next = reqoff; } ra->ra_winsize = RA_WINSIZE_SEQENTIAL; goto do_readahead; } /* * a request with UVM_ADV_NORMAL hint. (ie. no hint) * * we keep a sliding window in order to determine: * - if the previous read-ahead was successful or not. * - how many bytes to read-ahead. */ /* * if it's the first request for this context, * initialize context and return. */ if ((ra->ra_flags & RA_VALID) == 0) { initialize: ra->ra_winstart = ra->ra_next = reqoff + reqsize; ra->ra_winsize = RA_WINSIZE_INIT; ra->ra_flags |= RA_VALID; goto done; } /* * if it isn't in our window, * initialize context and return. * (read-ahead miss) */ if (reqoff < ra->ra_winstart || ra->ra_winstart + ra->ra_winsize < reqoff) { /* * ... unless we seem to be reading the same chunk repeatedly. * * XXX should have some margin? */ if (reqoff + reqsize == ra->ra_winstart) { DPRINTF(("%s: %p: same block: off=%" PRIu64 ", size=%zd, winstart=%" PRIu64 "\n", __func__, ra, reqoff, reqsize, ra->ra_winstart)); goto done; } goto initialize; } /* * it's in our window. (read-ahead hit) * - start read-ahead i/o if appropriate. * - advance and enlarge window. */ do_readahead: /* * don't bother to read-ahead behind current request. */ if (reqoff > ra->ra_next) { ra->ra_next = reqoff; } /* * try to make [reqoff, reqoff+ra_winsize) in-core. * note that [reqoff, ra_next) is considered already done. */ if (reqoff + ra->ra_winsize > ra->ra_next) { off_t raoff = MAX(reqoff, ra->ra_next); size_t rasize = reqoff + ra->ra_winsize - ra->ra_next; #if defined(DIAGNOSTIC) if (rasize > RA_WINSIZE_MAX) { /* * shouldn't happen as far as we're protected by * kernel_lock. */ printf("%s: corrupted context", __func__); rasize = RA_WINSIZE_MAX; } #endif /* defined(DIAGNOSTIC) */ /* * issue read-ahead only if we can start big enough i/o. * otherwise we end up with a stream of small i/o. */ if (rasize >= RA_MINSIZE) { ra->ra_next = ra_startio(uobj, raoff, rasize); } } /* * update window. * * enlarge window by reqsize, so that it grows in a predictable manner * regardless of the size of each read(2). */ ra->ra_winstart = reqoff + reqsize; ra->ra_winsize = MIN(RA_WINSIZE_MAX, ra->ra_winsize + reqsize); done:; }