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/*-
* See the file LICENSE for redistribution information.
*
* Copyright (c) 1996-2002
* Sleepycat Software. All rights reserved.
*/
#include "db_config.h"
#ifndef lint
static const char revid[] = "$Id: mp_alloc.c,v 1.1.1.1 2003/11/20 22:13:36 toshok Exp $";
#endif /* not lint */
#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>
#include <string.h>
#endif
#include "db_int.h"
#include "dbinc/db_shash.h"
#include "dbinc/mp.h"
typedef struct {
DB_MPOOL_HASH *bucket;
u_int32_t priority;
} HS;
static void __memp_bad_buffer __P((DB_MPOOL_HASH *));
static void __memp_reset_lru __P((DB_ENV *, REGINFO *, MPOOL *));
/*
* __memp_alloc --
* Allocate some space from a cache region.
*
* PUBLIC: int __memp_alloc __P((DB_MPOOL *,
* PUBLIC: REGINFO *, MPOOLFILE *, size_t, roff_t *, void *));
*/
int
__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;
DB_ENV *dbenv;
DB_MPOOL_HASH *dbht, *hp, *hp_end, *hp_tmp;
DB_MUTEX *mutexp;
MPOOL *c_mp;
MPOOLFILE *bh_mfp;
size_t freed_space;
u_int32_t buckets, buffers, high_priority, max_na, priority;
int aggressive, ret;
void *p;
dbenv = dbmp->dbenv;
c_mp = memreg->primary;
dbht = R_ADDR(memreg, c_mp->htab);
hp_end = &dbht[c_mp->htab_buckets];
buckets = buffers = 0;
aggressive = 0;
c_mp->stat.st_alloc++;
/*
* Get aggressive if we've tried to flush the number of pages as are
* in the system without finding space.
*/
max_na = 5 * c_mp->htab_buckets;
/*
* 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;
R_LOCK(dbenv, memreg);
/*
* On every buffer allocation we update the buffer generation number
* and check for wraparound.
*/
if (++c_mp->lru_count == UINT32_T_MAX)
__memp_reset_lru(dbenv, memreg, c_mp);
/*
* Anything newer than 1/10th of the buffer pool is ignored during
* allocation (unless allocation starts failing).
*/
DB_ASSERT(c_mp->lru_count > c_mp->stat.st_pages / 10);
high_priority = c_mp->lru_count - c_mp->stat.st_pages / 10;
/*
* First we try to allocate from free memory. If that fails, scan the
* buffer pool to find buffers with low priorities. We consider small
* sets of hash buckets each time to limit the amount of work needing
* to be done. This approximates LRU, but not very well. We either
* find a buffer of the same size to use, or we will free 3 times what
* we need in the hopes it will coalesce into a contiguous chunk of the
* right size. In the latter case we branch back here and try again.
*/
alloc: if ((ret = __db_shalloc(memreg->addr, len, MUTEX_ALIGN, &p)) == 0) {
if (mfp != NULL)
c_mp->stat.st_pages++;
R_UNLOCK(dbenv, memreg);
found: if (offsetp != NULL)
*offsetp = R_OFFSET(memreg, p);
*(void **)retp = p;
/*
* Update the search statistics.
*
* We're not holding the region locked here, these statistics
* can't be trusted.
*/
if (buckets != 0) {
if (buckets > c_mp->stat.st_alloc_max_buckets)
c_mp->stat.st_alloc_max_buckets = buckets;
c_mp->stat.st_alloc_buckets += buckets;
}
if (buffers != 0) {
if (buffers > c_mp->stat.st_alloc_max_pages)
c_mp->stat.st_alloc_max_pages = buffers;
c_mp->stat.st_alloc_pages += buffers;
}
return (0);
}
/*
* We re-attempt the allocation every time we've freed 3 times what
* we need. Reset our free-space counter.
*/
freed_space = 0;
/*
* Walk the hash buckets and find the next two with potentially useful
* buffers. Free the buffer with the lowest priority from the buckets'
* chains.
*/
for (hp_tmp = NULL;;) {
/* Check for wrap around. */
hp = &dbht[c_mp->last_checked++];
if (hp >= hp_end) {
c_mp->last_checked = 0;
/*
* If we've gone through all of the hash buckets, try
* an allocation. If the cache is small, the old page
* size is small, and the new page size is large, we
* might have freed enough memory (but not 3 times the
* memory).
*/
goto alloc;
}
/*
* Skip empty buckets.
*
* We can check for empty buckets before locking as we
* only care if the pointer is zero or non-zero.
*/
if (SH_TAILQ_FIRST(&hp->hash_bucket, __bh) == NULL)
continue;
/*
* The failure mode is when there are too many buffers we can't
* write or there's not enough memory in the system. We don't
* have a metric for deciding if allocation has no possible way
* to succeed, so we don't ever fail, we assume memory will be
* available if we wait long enough.
*
* Get aggressive if we've tried to flush 5 times the number of
* hash buckets as are in the system -- it's possible we have
* been repeatedly trying to flush the same buffers, although
* it's unlikely. Aggressive means:
*
* a: set a flag to attempt to flush high priority buffers as
* well as other buffers.
* b: sync the mpool to force out queue extent pages. While we
* might not have enough space for what we want and flushing
* is expensive, why not?
* c: sleep for a second -- hopefully someone else will run and
* free up some memory. Try to allocate memory too, in case
* the other thread returns its memory to the region.
* d: look at a buffer in every hash bucket rather than choose
* the more preferable of two.
*
* !!!
* This test ignores pathological cases like no buffers in the
* system -- that shouldn't be possible.
*/
if ((++buckets % max_na) == 0) {
aggressive = 1;
R_UNLOCK(dbenv, memreg);
(void)__memp_sync_int(
dbenv, NULL, 0, DB_SYNC_ALLOC, NULL);
(void)__os_sleep(dbenv, 1, 0);
R_LOCK(dbenv, memreg);
goto alloc;
}
if (!aggressive) {
/* Skip high priority buckets. */
if (hp->hash_priority > high_priority)
continue;
/*
* Find two buckets and select the one with the lowest
* priority. Performance testing shows that looking
* at two improves the LRUness and looking at more only
* does a little better.
*/
if (hp_tmp == NULL) {
hp_tmp = hp;
continue;
}
if (hp->hash_priority > hp_tmp->hash_priority)
hp = hp_tmp;
hp_tmp = NULL;
}
/* Remember the priority of the buffer we're looking for. */
priority = hp->hash_priority;
/* Unlock the region and lock the hash bucket. */
R_UNLOCK(dbenv, memreg);
mutexp = &hp->hash_mutex;
MUTEX_LOCK(dbenv, mutexp);
#ifdef DIAGNOSTIC
__memp_check_order(hp);
#endif
/*
* The lowest priority page is first in the bucket, as they are
* maintained in sorted order.
*
* The buffer may have been freed or its priority changed while
* we switched from the region lock to the hash lock. If so,
* we have to restart. We will still take the first buffer on
* the bucket's list, though, if it has a low enough priority.
*/
if ((bhp = SH_TAILQ_FIRST(&hp->hash_bucket, __bh)) == NULL ||
bhp->ref != 0 || bhp->priority > priority)
goto next_hb;
buffers++;
/* Find the associated MPOOLFILE. */
bh_mfp = R_ADDR(dbmp->reginfo, bhp->mf_offset);
/* If the page is dirty, pin it and write it. */
ret = 0;
if (F_ISSET(bhp, BH_DIRTY)) {
++bhp->ref;
ret = __memp_bhwrite(dbmp, hp, bh_mfp, bhp, 0);
--bhp->ref;
if (ret == 0)
++c_mp->stat.st_rw_evict;
} else
++c_mp->stat.st_ro_evict;
/*
* If a write fails for any reason, we can't proceed.
*
* We released the hash bucket lock while doing I/O, so another
* thread may have acquired this buffer and incremented the ref
* count after we wrote it, in which case we can't have it.
*
* If there's a write error, avoid selecting this buffer again
* by making it the bucket's least-desirable buffer.
*/
if (ret != 0 || bhp->ref != 0) {
if (ret != 0 && aggressive)
__memp_bad_buffer(hp);
goto next_hb;
}
/*
* Check to see if the buffer is the size we're looking for.
* If so, we can simply reuse it. Else, free the buffer and
* its space and keep looking.
*/
if (mfp != NULL &&
mfp->stat.st_pagesize == bh_mfp->stat.st_pagesize) {
__memp_bhfree(dbmp, hp, bhp, 0);
p = bhp;
goto found;
}
freed_space += __db_shsizeof(bhp);
__memp_bhfree(dbmp, hp, bhp, 1);
/*
* Unlock this hash bucket and re-acquire the region lock. If
* we're reaching here as a result of calling memp_bhfree, the
* hash bucket lock has already been discarded.
*/
if (0) {
next_hb: MUTEX_UNLOCK(dbenv, mutexp);
}
R_LOCK(dbenv, memreg);
/*
* Retry the allocation as soon as we've freed up sufficient
* space. We're likely to have to coalesce of memory to
* satisfy the request, don't try until it's likely (possible?)
* we'll succeed.
*/
if (freed_space >= 3 * len)
goto alloc;
}
/* NOTREACHED */
}
/*
* __memp_bad_buffer --
* Make the first buffer in a hash bucket the least desirable buffer.
*/
static void
__memp_bad_buffer(hp)
DB_MPOOL_HASH *hp;
{
BH *bhp, *t_bhp;
u_int32_t priority;
/* Remove the first buffer from the bucket. */
bhp = SH_TAILQ_FIRST(&hp->hash_bucket, __bh);
SH_TAILQ_REMOVE(&hp->hash_bucket, bhp, hq, __bh);
/*
* Find the highest priority buffer in the bucket. Buffers are
* sorted by priority, so it's the last one in the bucket.
*
* XXX
* Should use SH_TAILQ_LAST, but I think that macro is broken.
*/
priority = bhp->priority;
for (t_bhp = SH_TAILQ_FIRST(&hp->hash_bucket, __bh);
t_bhp != NULL; t_bhp = SH_TAILQ_NEXT(t_bhp, hq, __bh))
priority = t_bhp->priority;
/*
* Set our buffer's priority to be just as bad, and append it to
* the bucket.
*/
bhp->priority = priority;
SH_TAILQ_INSERT_TAIL(&hp->hash_bucket, bhp, hq);
/* Reset the hash bucket's priority. */
hp->hash_priority = SH_TAILQ_FIRST(&hp->hash_bucket, __bh)->priority;
}
/*
* __memp_reset_lru --
* Reset the cache LRU counter.
*/
static void
__memp_reset_lru(dbenv, memreg, c_mp)
DB_ENV *dbenv;
REGINFO *memreg;
MPOOL *c_mp;
{
BH *bhp;
DB_MPOOL_HASH *hp;
int bucket;
/*
* Update the counter so all future allocations will start at the
* bottom.
*/
c_mp->lru_count -= MPOOL_BASE_DECREMENT;
/* Release the region lock. */
R_UNLOCK(dbenv, memreg);
/* Adjust the priority of every buffer in the system. */
for (hp = R_ADDR(memreg, c_mp->htab),
bucket = 0; bucket < c_mp->htab_buckets; ++hp, ++bucket) {
/*
* Skip empty buckets.
*
* We can check for empty buckets before locking as we
* only care if the pointer is zero or non-zero.
*/
if (SH_TAILQ_FIRST(&hp->hash_bucket, __bh) == NULL)
continue;
MUTEX_LOCK(dbenv, &hp->hash_mutex);
for (bhp = SH_TAILQ_FIRST(&hp->hash_bucket, __bh);
bhp != NULL; bhp = SH_TAILQ_NEXT(bhp, hq, __bh))
if (bhp->priority != UINT32_T_MAX &&
bhp->priority > MPOOL_BASE_DECREMENT)
bhp->priority -= MPOOL_BASE_DECREMENT;
MUTEX_UNLOCK(dbenv, &hp->hash_mutex);
}
/* Reacquire the region lock. */
R_LOCK(dbenv, memreg);
}
#ifdef DIAGNOSTIC
/*
* __memp_check_order --
* Verify the priority ordering of a hash bucket chain.
*
* PUBLIC: #ifdef DIAGNOSTIC
* PUBLIC: void __memp_check_order __P((DB_MPOOL_HASH *));
* PUBLIC: #endif
*/
void
__memp_check_order(hp)
DB_MPOOL_HASH *hp;
{
BH *bhp;
u_int32_t priority;
/*
* Assumes the hash bucket is locked.
*/
if ((bhp = SH_TAILQ_FIRST(&hp->hash_bucket, __bh)) == NULL)
return;
DB_ASSERT(bhp->priority == hp->hash_priority);
for (priority = bhp->priority;
(bhp = SH_TAILQ_NEXT(bhp, hq, __bh)) != NULL;
priority = bhp->priority)
DB_ASSERT(priority <= bhp->priority);
}
#endif
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