mp_alloc.c

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/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 1997, 1998, 1999, 2000
 *      Sleepycat Software.  All rights reserved.
 */
#include "config.h"

#ifndef lint
static const char revid[] = "$Id: mp__alloc_8c-source.html,v 1.1 2008/06/08 10:20:39 sebdiaz Exp $";
#endif /* not lint */

#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>
#endif

#include "db_int.h"
#include "db_shash.h"
#include "mp.h"

/*
 * CDB___memp_alloc --
 *      Allocate some space from a cache region.
 *
 * PUBLIC: int CDB___memp_alloc __P((DB_MPOOL *,
 * PUBLIC:     REGINFO *, MPOOLFILE *, size_t, roff_t *, void *));
 */
int
CDB___memp_alloc(dbmp, memreg, mfp, len, offsetp, retp)
        DB_MPOOL *dbmp;
        REGINFO *memreg;
        MPOOLFILE *mfp;
        size_t len;
        roff_t *offsetp;
        void *retp;
{
        BH *bhp, *nbhp;
        MPOOL *c_mp;
        MPOOLFILE *bh_mfp;
        size_t total;
        int nomore, restart, ret, wrote;
        void *p;

        c_mp = memreg->primary;

        /*
         * If we're allocating a buffer, and the one we're discarding is the
         * same size, we don't want to waste the time to re-integrate it into
         * the shared memory free list.  If the DB_MPOOLFILE argument isn't
         * NULL, we'll compare the underlying page sizes of the two buffers
         * before free-ing and re-allocating buffers.
         */
        if (mfp != NULL)
                len = (sizeof(BH) - sizeof(u_int8_t)) + mfp->stat.st_pagesize;

        nomore = 0;
alloc:  if ((ret = CDB___db_shalloc(memreg->addr, len, MUTEX_ALIGN, &p)) == 0) {
                if (offsetp != NULL)
                        *offsetp = R_OFFSET(memreg, p);
                *(void **)retp = p;
                return (0);
        }
        if (nomore) {
                CDB___db_err(dbmp->dbenv,
            "Unable to allocate %lu bytes from mpool shared region: %s\n",
                    (u_long)len, CDB_db_strerror(ret));
                return (ret);
        }

retry:  /* Find a buffer we can flush; pure LRU. */
        restart = total = 0;
        for (bhp =
            SH_TAILQ_FIRST(&c_mp->bhq, __bh); bhp != NULL; bhp = nbhp) {
                nbhp = SH_TAILQ_NEXT(bhp, q, __bh);

                /* Ignore pinned or locked (I/O in progress) buffers. */
                if (bhp->ref != 0 || F_ISSET(bhp, BH_LOCKED))
                        continue;

                /* Find the associated MPOOLFILE. */
                bh_mfp = R_ADDR(dbmp->reginfo, bhp->mf_offset);

                /* Write the page if it's dirty. */
                if (F_ISSET(bhp, BH_DIRTY)) {
                        ++bhp->ref;
                        if ((ret = CDB___memp_bhwrite(dbmp,
                            bh_mfp, bhp, &restart, &wrote)) != 0)
                                return (ret);
                        --bhp->ref;

                        /*
                         * Another process may have acquired this buffer and
                         * incremented the ref count after we wrote it.
                         */
                        if (bhp->ref != 0)
                                goto retry;

                        /*
                         * If we wrote the page, continue and free the buffer.
                         * We don't have to rewalk the list to acquire the
                         * buffer because it was never available for any other
                         * process to modify it.
                         *
                         * If we didn't write the page, but we discarded and
                         * reacquired the region lock, restart the list walk.
                         *
                         * If we neither wrote the buffer nor discarded the
                         * region lock, continue down the buffer list.
                         */
                        if (wrote)
                                ++c_mp->stat.st_rw_evict;
                        else {
                                if (restart)
                                        goto retry;
                                continue;
                        }
                } else
                        ++c_mp->stat.st_ro_evict;

                /*
                 * Check to see if the buffer is the size we're looking for.
                 * If it is, simply reuse it.
                 */
                if (mfp != NULL &&
                    mfp->stat.st_pagesize == bh_mfp->stat.st_pagesize) {
                        CDB___memp_bhfree(dbmp, bhp, 0);

                        if (offsetp != NULL)
                                *offsetp = R_OFFSET(memreg, bhp);
                        *(void **)retp = bhp;
                        return (0);
                }

                /* Note how much space we've freed, and free the buffer. */
                total += CDB___db_shsizeof(bhp);
                CDB___memp_bhfree(dbmp, bhp, 1);

                /*
                 * Retry as soon as we've freed up sufficient space.  If we
                 * have to coalesce of memory to satisfy the request, don't
                 * try until it's likely (possible?) that we'll succeed.
                 */
                if (total >= 3 * len)
                        goto alloc;

                /* Restart the walk if we discarded the region lock. */
                if (restart)
                        goto retry;
        }
        nomore = 1;
        goto alloc;
}

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