From 4d3fc5711202a7d13538b662190807617ae2df65 Mon Sep 17 00:00:00 2001 From: Ned Bass Date: Fri, 30 Jul 2010 16:06:41 -0700 Subject: [PATCH] Reduce stack usage for recursive dbuf_hold_impl() 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 34229a2f2ac07363f64ddd63e014964fff2f0671 which reduced stack usage of traverse_visitbp(). dbuf_hold_impl() is mutually recursive with dbuf_findbp(), but the latter function is also called from other functions. Therefore dbuf_findbp() must contain logic to determine how to call dbuf_hold_impl(). To this end, dbuf_hold_impl() now takes a struct dbuf_hold_impl_data pointer as an argument. If that argument is NULL it calls dbuf_hold_impl() as before, otherwise it calls __debuf_hold_impl() with a single dbuf_hold_impl_data pointer argument. As the name implies, dbuf_hold_impl_data stores the arguments and local variables for dbuf_hold_impl(). Signed-off-by: Brian Behlendorf --- module/zfs/dbuf.c | 192 ++++++++++++++++++++++++++++++++-------------- 1 file changed, 134 insertions(+), 58 deletions(-) diff --git a/module/zfs/dbuf.c b/module/zfs/dbuf.c index 42ae439972..b023fdd766 100644 --- a/module/zfs/dbuf.c +++ b/module/zfs/dbuf.c @@ -36,6 +36,29 @@ #include #include +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); @@ -1492,7 +1515,7 @@ 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; @@ -1529,8 +1552,17 @@ 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, @@ -1723,7 +1755,7 @@ dbuf_prefetch(dnode_t *dn, uint64_t blkid) db = NULL; } - 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; @@ -1750,98 +1782,142 @@ 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); + dh->dh_db = dbuf_find(dh->dh_dn, dh->dh_level, dh->dh_blkid); - if (db == NULL) { - blkptr_t *bp = NULL; - int err; + if (dh->dh_db == NULL) { + dh->dh_bp = NULL; - 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); + 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 (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 (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_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 (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 (dr->dt.dl.dr_data == db->db_buf) { - arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db); + 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(db, - arc_buf_alloc(db->db_dnode->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); + dbuf_set_data(dh->dh_db, + arc_buf_alloc(dh->dh_db->db_dnode->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->db_dnode, ==, dn); - ASSERT3U(db->db_blkid, ==, blkid); - ASSERT3U(db->db_level, ==, level); - *dbp = db; + ASSERT3P(dh->dh_db->db_dnode, ==, 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) {