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Fix stack dbuf_hold_impl()
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This commit preserves the recursive function dbuf_hold_impl() but moves
the local variables and function arguments to the heap to minimize
the stack frame size.  Enough space is initially allocated on the
stack for 20 levels of recursion.  This technique was based on commit
34229a2 which reduced stack usage of
traverse_visitbp().

Signed-off-by: Brian Behlendorf <[email protected]>
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@behlendorf
behlendorf committed Aug 31, 2010
1 parent 5ac1241 commit fc5bb51
Showing 1 changed file with 140 additions and 64 deletions.
204 changes: 140 additions & 64 deletions module/zfs/dbuf.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,29 @@
#include <sys/sa.h>
#include <sys/sa_impl.h>

struct dbuf_hold_impl_data {
/* Function arguments */
dnode_t *dh_dn;
uint8_t dh_level;
uint64_t dh_blkid;
int dh_fail_sparse;
void *dh_tag;
dmu_buf_impl_t **dh_dbp;
/* Local variables */
dmu_buf_impl_t *dh_db;
dmu_buf_impl_t *dh_parent;
blkptr_t *dh_bp;
int dh_err;
dbuf_dirty_record_t *dh_dr;
arc_buf_contents_t dh_type;
int dh_depth;
};

static void __dbuf_hold_impl_init(struct dbuf_hold_impl_data *dh,
dnode_t *dn, uint8_t level, uint64_t blkid, int fail_sparse,
void *tag, dmu_buf_impl_t **dbp, int depth);
static int __dbuf_hold_impl(struct dbuf_hold_impl_data *dh);

static void dbuf_destroy(dmu_buf_impl_t *db);
static int dbuf_undirty(dmu_buf_impl_t *db, dmu_tx_t *tx);
static void dbuf_write(dbuf_dirty_record_t *dr, arc_buf_t *data, dmu_tx_t *tx);
Expand Down Expand Up @@ -1586,7 +1609,7 @@ dbuf_clear(dmu_buf_impl_t *db)

static int
dbuf_findbp(dnode_t *dn, int level, uint64_t blkid, int fail_sparse,
dmu_buf_impl_t **parentp, blkptr_t **bpp)
dmu_buf_impl_t **parentp, blkptr_t **bpp, struct dbuf_hold_impl_data *dh)
{
int nlevels, epbs;

Expand Down Expand Up @@ -1623,8 +1646,17 @@ dbuf_findbp(dnode_t *dn, int level, uint64_t blkid, int fail_sparse,
return (ENOENT);
} else if (level < nlevels-1) {
/* this block is referenced from an indirect block */
int err = dbuf_hold_impl(dn, level+1,
blkid >> epbs, fail_sparse, NULL, parentp);
int err;
if (dh == NULL) {
err = dbuf_hold_impl(dn, level+1, blkid >> epbs,
fail_sparse, NULL, parentp);
}
else {
__dbuf_hold_impl_init(dh + 1, dn, dh->dh_level + 1,
blkid >> epbs, fail_sparse, NULL,
parentp, dh->dh_depth + 1);
err = __dbuf_hold_impl(dh + 1);
}
if (err)
return (err);
err = dbuf_read(*parentp, NULL,
Expand Down Expand Up @@ -1823,7 +1855,7 @@ dbuf_prefetch(dnode_t *dn, uint64_t blkid)
return;
}

if (dbuf_findbp(dn, 0, blkid, TRUE, &db, &bp) == 0) {
if (dbuf_findbp(dn, 0, blkid, TRUE, &db, &bp, NULL) == 0) {
if (bp && !BP_IS_HOLE(bp)) {
int priority = dn->dn_type == DMU_OT_DDT_ZAP ?
ZIO_PRIORITY_DDT_PREFETCH : ZIO_PRIORITY_ASYNC_READ;
Expand All @@ -1850,98 +1882,142 @@ dbuf_prefetch(dnode_t *dn, uint64_t blkid)
}
}

#define DBUF_HOLD_IMPL_MAX_DEPTH 20

/*
* Returns with db_holds incremented, and db_mtx not held.
* Note: dn_struct_rwlock must be held.
*/
int
dbuf_hold_impl(dnode_t *dn, uint8_t level, uint64_t blkid, int fail_sparse,
void *tag, dmu_buf_impl_t **dbp)
static int
__dbuf_hold_impl(struct dbuf_hold_impl_data *dh)
{
dmu_buf_impl_t *db, *parent = NULL;
ASSERT3S(dh->dh_depth, <, DBUF_HOLD_IMPL_MAX_DEPTH);
dh->dh_parent = NULL;

ASSERT(blkid != DMU_BONUS_BLKID);
ASSERT(RW_LOCK_HELD(&dn->dn_struct_rwlock));
ASSERT3U(dn->dn_nlevels, >, level);
ASSERT(dh->dh_blkid != DMU_BONUS_BLKID);
ASSERT(RW_LOCK_HELD(&dh->dh_dn->dn_struct_rwlock));
ASSERT3U(dh->dh_dn->dn_nlevels, >, dh->dh_level);

*dbp = NULL;
*(dh->dh_dbp) = NULL;
top:
/* dbuf_find() returns with db_mtx held */
db = dbuf_find(dn, level, blkid);

if (db == NULL) {
blkptr_t *bp = NULL;
int err;

ASSERT3P(parent, ==, NULL);
err = dbuf_findbp(dn, level, blkid, fail_sparse, &parent, &bp);
if (fail_sparse) {
if (err == 0 && bp && BP_IS_HOLE(bp))
err = ENOENT;
if (err) {
if (parent)
dbuf_rele(parent, NULL);
return (err);
dh->dh_db = dbuf_find(dh->dh_dn, dh->dh_level, dh->dh_blkid);

if (dh->dh_db == NULL) {
dh->dh_bp = NULL;

ASSERT3P(dh->dh_parent, ==, NULL);
dh->dh_err = dbuf_findbp(dh->dh_dn, dh->dh_level, dh->dh_blkid,
dh->dh_fail_sparse, &dh->dh_parent,
&dh->dh_bp, dh);
if (dh->dh_fail_sparse) {
if (dh->dh_err == 0 && dh->dh_bp && BP_IS_HOLE(dh->dh_bp))
dh->dh_err = ENOENT;
if (dh->dh_err) {
if (dh->dh_parent)
dbuf_rele(dh->dh_parent, NULL);
return (dh->dh_err);
}
}
if (err && err != ENOENT)
return (err);
db = dbuf_create(dn, level, blkid, parent, bp);
}

if (db->db_buf && refcount_is_zero(&db->db_holds)) {
arc_buf_add_ref(db->db_buf, db);
if (db->db_buf->b_data == NULL) {
dbuf_clear(db);
if (parent) {
dbuf_rele(parent, NULL);
parent = NULL;
if (dh->dh_err && dh->dh_err != ENOENT)
return (dh->dh_err);
dh->dh_db = dbuf_create(dh->dh_dn, dh->dh_level, dh->dh_blkid,
dh->dh_parent, dh->dh_bp);
}

if (dh->dh_db->db_buf && refcount_is_zero(&dh->dh_db->db_holds)) {
arc_buf_add_ref(dh->dh_db->db_buf, dh->dh_db);
if (dh->dh_db->db_buf->b_data == NULL) {
dbuf_clear(dh->dh_db);
if (dh->dh_parent) {
dbuf_rele(dh->dh_parent, NULL);
dh->dh_parent = NULL;
}
goto top;
}
ASSERT3P(db->db.db_data, ==, db->db_buf->b_data);
ASSERT3P(dh->dh_db->db.db_data, ==, dh->dh_db->db_buf->b_data);
}

ASSERT(db->db_buf == NULL || arc_referenced(db->db_buf));
ASSERT(dh->dh_db->db_buf == NULL || arc_referenced(dh->dh_db->db_buf));

/*
* If this buffer is currently syncing out, and we are are
* still referencing it from db_data, we need to make a copy
* of it in case we decide we want to dirty it again in this txg.
*/
if (db->db_level == 0 && db->db_blkid != DMU_BONUS_BLKID &&
dn->dn_object != DMU_META_DNODE_OBJECT &&
db->db_state == DB_CACHED && db->db_data_pending) {
dbuf_dirty_record_t *dr = db->db_data_pending;

if (dr->dt.dl.dr_data == db->db_buf) {
arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db);

dbuf_set_data(db,
arc_buf_alloc(dn->dn_objset->os_spa,
db->db.db_size, db, type));
bcopy(dr->dt.dl.dr_data->b_data, db->db.db_data,
db->db.db_size);
if (dh->dh_db->db_level == 0 &&
dh->dh_db->db_blkid != DMU_BONUS_BLKID &&
dh->dh_dn->dn_object != DMU_META_DNODE_OBJECT &&
dh->dh_db->db_state == DB_CACHED && dh->dh_db->db_data_pending) {
dh->dh_dr = dh->dh_db->db_data_pending;

if (dh->dh_dr->dt.dl.dr_data == dh->dh_db->db_buf) {
dh->dh_type = DBUF_GET_BUFC_TYPE(dh->dh_db);

dbuf_set_data(dh->dh_db,
arc_buf_alloc(dh->dh_dn->dn_objset->os_spa,
dh->dh_db->db.db_size, dh->dh_db, dh->dh_type));
bcopy(dh->dh_dr->dt.dl.dr_data->b_data,
dh->dh_db->db.db_data, dh->dh_db->db.db_size);
}
}

(void) refcount_add(&db->db_holds, tag);
dbuf_update_data(db);
DBUF_VERIFY(db);
mutex_exit(&db->db_mtx);
(void) refcount_add(&dh->dh_db->db_holds, dh->dh_tag);
dbuf_update_data(dh->dh_db);
DBUF_VERIFY(dh->dh_db);
mutex_exit(&dh->dh_db->db_mtx);

/* NOTE: we can't rele the parent until after we drop the db_mtx */
if (parent)
dbuf_rele(parent, NULL);
if (dh->dh_parent)
dbuf_rele(dh->dh_parent, NULL);

ASSERT3P(DB_DNODE(db), ==, dn);
ASSERT3U(db->db_blkid, ==, blkid);
ASSERT3U(db->db_level, ==, level);
*dbp = db;
ASSERT3P(DB_DNODE(dh->dh_db), ==, dh->dh_dn);
ASSERT3U(dh->dh_db->db_blkid, ==, dh->dh_blkid);
ASSERT3U(dh->dh_db->db_level, ==, dh->dh_level);
*(dh->dh_dbp) = dh->dh_db;

return (0);
}

/*
* The following code preserves the recursive function dbuf_hold_impl()
* but moves the local variables AND function arguments to the heap to
* minimize the stack frame size. Enough space is initially allocated
* on the stack for 20 levels of recursion.
*/
int
dbuf_hold_impl(dnode_t *dn, uint8_t level, uint64_t blkid, int fail_sparse,
void *tag, dmu_buf_impl_t **dbp)
{
struct dbuf_hold_impl_data *dh;
int error;

dh = kmem_zalloc(sizeof(struct dbuf_hold_impl_data) *
DBUF_HOLD_IMPL_MAX_DEPTH, KM_SLEEP);
__dbuf_hold_impl_init(dh, dn, level, blkid, fail_sparse, tag, dbp, 0);

error = __dbuf_hold_impl(dh);

kmem_free(dh, sizeof(struct dbuf_hold_impl_data) *
DBUF_HOLD_IMPL_MAX_DEPTH);

return (error);
}

static void
__dbuf_hold_impl_init(struct dbuf_hold_impl_data *dh,
dnode_t *dn, uint8_t level, uint64_t blkid, int fail_sparse,
void *tag, dmu_buf_impl_t **dbp, int depth)
{
dh->dh_dn = dn;
dh->dh_level = level;
dh->dh_blkid = blkid;
dh->dh_fail_sparse = fail_sparse;
dh->dh_tag = tag;
dh->dh_dbp = dbp;
dh->dh_depth = depth;
}

dmu_buf_impl_t *
dbuf_hold(dnode_t *dn, uint64_t blkid, void *tag)
{
Expand Down

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