From 34229a2f2ac07363f64ddd63e014964fff2f0671 Mon Sep 17 00:00:00 2001 From: Brian Behlendorf Date: Tue, 29 Jun 2010 11:04:26 -0700 Subject: [PATCH] Reduce stack usage for recursive traverse_visitbp() Due to limited stack space recursive functions are frowned upon in the Linux kernel. However, they often are the most elegant solution to a problem. The following code preserves the recursive function traverse_visitbp() 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 change does ugly-up-the-code but it reduces the worst case usage from roughly 4160 bytes to 960 bytes on x86_64 archs. --- .topdeps | 1 + .topmsg | 13 ++ module/zfs/dmu_traverse.c | 273 ++++++++++++++++++++++++-------------- 3 files changed, 191 insertions(+), 96 deletions(-) create mode 100644 .topdeps create mode 100644 .topmsg diff --git a/.topdeps b/.topdeps new file mode 100644 index 0000000000..1f7391f92b --- /dev/null +++ b/.topdeps @@ -0,0 +1 @@ +master diff --git a/.topmsg b/.topmsg new file mode 100644 index 0000000000..0c9201a1a8 --- /dev/null +++ b/.topmsg @@ -0,0 +1,13 @@ +From: Brian Behlendorf +Subject: [PATCH] fix stack traverse_visitbp + +Due to limited stack space recursive functions are frowned upon in +the Linux kernel. However, they often are the most elegant solution +to a problem. The following code preserves the recursive function +traverse_visitbp() 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 change does ugly-up-the-code but it reduces the worst case +usage from roughly 4160 bytes to 960 bytes on x86_64 archs. + +Signed-off-by: Brian Behlendorf diff --git a/module/zfs/dmu_traverse.c b/module/zfs/dmu_traverse.c index 429c76ae11..2cf10df828 100644 --- a/module/zfs/dmu_traverse.c +++ b/module/zfs/dmu_traverse.c @@ -57,6 +57,33 @@ struct traverse_data { void *td_arg; }; +struct traverse_visitbp_data { + /* Function arguments */ + struct traverse_data *tv_td; + const dnode_phys_t *tv_dnp; + arc_buf_t *tv_pbuf; + blkptr_t *tv_bp; + const zbookmark_t *tv_zb; + /* Local variables */ + struct prefetch_data *tv_pd; + zbookmark_t tv_czb; + arc_buf_t *tv_buf; + boolean_t tv_hard; + objset_phys_t *tv_osp; + dnode_phys_t *tv_ldnp; + blkptr_t *tv_cbp; + uint32_t tv_flags; + int tv_err; + int tv_lasterr; + int tv_i; + int tv_epb; +#ifdef DEBUG + int tv_depth; +#endif +}; + +static inline int traverse_visitbp(struct traverse_data *td, const + dnode_phys_t *dnp, arc_buf_t *pbuf, blkptr_t *bp, const zbookmark_t *zb); static int traverse_dnode(struct traverse_data *td, const dnode_phys_t *dnp, arc_buf_t *buf, uint64_t objset, uint64_t object); @@ -128,137 +155,191 @@ traverse_zil(struct traverse_data *td, zil_header_t *zh) zil_free(zilog); } -static int -traverse_visitbp(struct traverse_data *td, const dnode_phys_t *dnp, - arc_buf_t *pbuf, blkptr_t *bp, const zbookmark_t *zb) -{ - zbookmark_t czb; - int err = 0, lasterr = 0; - arc_buf_t *buf = NULL; - struct prefetch_data *pd = td->td_pfd; - boolean_t hard = td->td_flags & TRAVERSE_HARD; +#define TRAVERSE_VISITBP_MAX_DEPTH 20 - if (bp->blk_birth == 0) { - err = td->td_func(td->td_spa, NULL, NULL, pbuf, zb, dnp, - td->td_arg); - return (err); +static void +__traverse_visitbp_init(struct traverse_visitbp_data *tv, + struct traverse_data *td, const dnode_phys_t *dnp, + arc_buf_t *pbuf, blkptr_t *bp, const zbookmark_t *zb, int depth) +{ + tv->tv_td = td; + tv->tv_dnp = dnp; + tv->tv_pbuf = pbuf; + tv->tv_bp = bp; + tv->tv_zb = zb; + tv->tv_err = 0; + tv->tv_lasterr = 0; + tv->tv_buf = NULL; + tv->tv_pd = td->td_pfd; + tv->tv_hard = td->td_flags & TRAVERSE_HARD; + tv->tv_flags = ARC_WAIT; + tv->tv_depth = depth; +} + +static noinline int +__traverse_visitbp(struct traverse_visitbp_data *tv) +{ + ASSERT3S(tv->tv_depth, <, TRAVERSE_VISITBP_MAX_DEPTH); + + if (tv->tv_bp->blk_birth == 0) { + tv->tv_err = tv->tv_td->td_func(tv->tv_td->td_spa, NULL, NULL, + tv->tv_pbuf, tv->tv_zb, tv->tv_dnp, tv->tv_td->td_arg); + return (tv->tv_err); } - if (bp->blk_birth <= td->td_min_txg) + if (tv->tv_bp->blk_birth <= tv->tv_td->td_min_txg) return (0); - if (pd && !pd->pd_exited && - ((pd->pd_flags & TRAVERSE_PREFETCH_DATA) || - BP_GET_TYPE(bp) == DMU_OT_DNODE || BP_GET_LEVEL(bp) > 0)) { - mutex_enter(&pd->pd_mtx); - ASSERT(pd->pd_blks_fetched >= 0); - while (pd->pd_blks_fetched == 0 && !pd->pd_exited) - cv_wait(&pd->pd_cv, &pd->pd_mtx); - pd->pd_blks_fetched--; - cv_broadcast(&pd->pd_cv); - mutex_exit(&pd->pd_mtx); + if (tv->tv_pd && !tv->tv_pd->pd_exited && + ((tv->tv_pd->pd_flags & TRAVERSE_PREFETCH_DATA) || + BP_GET_TYPE(tv->tv_bp) == DMU_OT_DNODE || + BP_GET_LEVEL(tv->tv_bp) > 0)) { + mutex_enter(&tv->tv_pd->pd_mtx); + ASSERT(tv->tv_pd->pd_blks_fetched >= 0); + while (tv->tv_pd->pd_blks_fetched == 0 && !tv->tv_pd->pd_exited) + cv_wait(&tv->tv_pd->pd_cv, &tv->tv_pd->pd_mtx); + tv->tv_pd->pd_blks_fetched--; + cv_broadcast(&tv->tv_pd->pd_cv); + mutex_exit(&tv->tv_pd->pd_mtx); } - if (td->td_flags & TRAVERSE_PRE) { - err = td->td_func(td->td_spa, NULL, bp, pbuf, zb, dnp, - td->td_arg); - if (err) - return (err); + if (tv->tv_td->td_flags & TRAVERSE_PRE) { + tv->tv_err = tv->tv_td->td_func(tv->tv_td->td_spa, NULL, + tv->tv_bp, tv->tv_pbuf, tv->tv_zb, tv->tv_dnp, + tv->tv_td->td_arg); + if (tv->tv_err) + return (tv->tv_err); } - if (BP_GET_LEVEL(bp) > 0) { - uint32_t flags = ARC_WAIT; - int i; - blkptr_t *cbp; - int epb = BP_GET_LSIZE(bp) >> SPA_BLKPTRSHIFT; + if (BP_GET_LEVEL(tv->tv_bp) > 0) { + tv->tv_epb = BP_GET_LSIZE(tv->tv_bp) >> SPA_BLKPTRSHIFT; - err = dsl_read(NULL, td->td_spa, bp, pbuf, - arc_getbuf_func, &buf, - ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, &flags, zb); - if (err) - return (err); + tv->tv_err = dsl_read(NULL, tv->tv_td->td_spa, tv->tv_bp, + tv->tv_pbuf, arc_getbuf_func, &tv->tv_buf, + ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, + &tv->tv_flags, tv->tv_zb); + if (tv->tv_err) + return (tv->tv_err); /* recursively visitbp() blocks below this */ - cbp = buf->b_data; - for (i = 0; i < epb; i++, cbp++) { - SET_BOOKMARK(&czb, zb->zb_objset, zb->zb_object, - zb->zb_level - 1, - zb->zb_blkid * epb + i); - err = traverse_visitbp(td, dnp, buf, cbp, &czb); - if (err) { - if (!hard) + tv->tv_cbp = tv->tv_buf->b_data; + for (tv->tv_i = 0; tv->tv_i < tv->tv_epb; + tv->tv_i++, tv->tv_cbp++) { + SET_BOOKMARK(&tv->tv_czb, tv->tv_zb->zb_objset, + tv->tv_zb->zb_object, tv->tv_zb->zb_level - 1, + tv->tv_zb->zb_blkid * tv->tv_epb + tv->tv_i); + __traverse_visitbp_init(tv + 1, tv->tv_td, + tv->tv_dnp, tv->tv_buf, tv->tv_cbp, + &tv->tv_czb, tv->tv_depth + 1); + tv->tv_err = __traverse_visitbp(tv + 1); + if (tv->tv_err) { + if (!tv->tv_hard) break; - lasterr = err; + tv->tv_lasterr = tv->tv_err; } } - } else if (BP_GET_TYPE(bp) == DMU_OT_DNODE) { - uint32_t flags = ARC_WAIT; - int i; - int epb = BP_GET_LSIZE(bp) >> DNODE_SHIFT; + } else if (BP_GET_TYPE(tv->tv_bp) == DMU_OT_DNODE) { + tv->tv_epb = BP_GET_LSIZE(tv->tv_bp) >> DNODE_SHIFT; - err = dsl_read(NULL, td->td_spa, bp, pbuf, - arc_getbuf_func, &buf, - ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, &flags, zb); - if (err) - return (err); + tv->tv_err = dsl_read(NULL, tv->tv_td->td_spa, tv->tv_bp, + tv->tv_pbuf, arc_getbuf_func, &tv->tv_buf, + ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, + &tv->tv_flags, tv->tv_zb); + if (tv->tv_err) + return (tv->tv_err); /* recursively visitbp() blocks below this */ - dnp = buf->b_data; - for (i = 0; i < epb; i++, dnp++) { - err = traverse_dnode(td, dnp, buf, zb->zb_objset, - zb->zb_blkid * epb + i); - if (err) { - if (!hard) + tv->tv_dnp = tv->tv_buf->b_data; + for (tv->tv_i = 0; tv->tv_i < tv->tv_epb; + tv->tv_i++, tv->tv_dnp++) { + tv->tv_err = traverse_dnode(tv->tv_td, tv->tv_dnp, + tv->tv_buf, tv->tv_zb->zb_objset, + tv->tv_zb->zb_blkid * tv->tv_epb + tv->tv_i); + if (tv->tv_err) { + if (!tv->tv_hard) break; - lasterr = err; + tv->tv_lasterr = tv->tv_err; } } - } else if (BP_GET_TYPE(bp) == DMU_OT_OBJSET) { - uint32_t flags = ARC_WAIT; - objset_phys_t *osp; - dnode_phys_t *dnp; + } else if (BP_GET_TYPE(tv->tv_bp) == DMU_OT_OBJSET) { - err = dsl_read_nolock(NULL, td->td_spa, bp, - arc_getbuf_func, &buf, - ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, &flags, zb); - if (err) - return (err); + tv->tv_err = dsl_read_nolock(NULL, tv->tv_td->td_spa, + tv->tv_bp, arc_getbuf_func, &tv->tv_buf, + ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, + &tv->tv_flags, tv->tv_zb); + if (tv->tv_err) + return (tv->tv_err); - osp = buf->b_data; - traverse_zil(td, &osp->os_zil_header); + tv->tv_osp = tv->tv_buf->b_data; + traverse_zil(tv->tv_td, &tv->tv_osp->os_zil_header); - dnp = &osp->os_meta_dnode; - err = traverse_dnode(td, dnp, buf, zb->zb_objset, - DMU_META_DNODE_OBJECT); - if (err && hard) { - lasterr = err; - err = 0; + tv->tv_ldnp = &tv->tv_osp->os_meta_dnode; + tv->tv_err = traverse_dnode(tv->tv_td, tv->tv_ldnp, tv->tv_buf, + tv->tv_zb->zb_objset, DMU_META_DNODE_OBJECT); + if (tv->tv_err && tv->tv_hard) { + tv->tv_lasterr = tv->tv_err; + tv->tv_err = 0; } - if (err == 0 && arc_buf_size(buf) >= sizeof (objset_phys_t)) { - dnp = &osp->os_userused_dnode; - err = traverse_dnode(td, dnp, buf, zb->zb_objset, + if (tv->tv_err == 0 && + arc_buf_size(tv->tv_buf) >= sizeof (objset_phys_t)) { + tv->tv_ldnp = &tv->tv_osp->os_userused_dnode; + tv->tv_err = traverse_dnode(tv->tv_td, tv->tv_ldnp, + tv->tv_buf, tv->tv_zb->zb_objset, DMU_USERUSED_OBJECT); } - if (err && hard) { - lasterr = err; - err = 0; + if (tv->tv_err && tv->tv_hard) { + tv->tv_lasterr = tv->tv_err; + tv->tv_err = 0; } - if (err == 0 && arc_buf_size(buf) >= sizeof (objset_phys_t)) { - dnp = &osp->os_groupused_dnode; - err = traverse_dnode(td, dnp, buf, zb->zb_objset, + if (tv->tv_err == 0 && + arc_buf_size(tv->tv_buf) >= sizeof (objset_phys_t)) { + tv->tv_ldnp = &tv->tv_osp->os_groupused_dnode; + tv->tv_err = traverse_dnode(tv->tv_td, tv->tv_ldnp, + tv->tv_buf, tv->tv_zb->zb_objset, DMU_GROUPUSED_OBJECT); } } - if (buf) - (void) arc_buf_remove_ref(buf, &buf); + if (tv->tv_buf) + (void) arc_buf_remove_ref(tv->tv_buf, &tv->tv_buf); - if (err == 0 && lasterr == 0 && (td->td_flags & TRAVERSE_POST)) { - err = td->td_func(td->td_spa, NULL, bp, pbuf, zb, dnp, - td->td_arg); + if (tv->tv_err == 0 && tv->tv_lasterr == 0 && + (tv->tv_td->td_flags & TRAVERSE_POST)) { + tv->tv_err = tv->tv_td->td_func(tv->tv_td->td_spa, NULL, + tv->tv_bp, tv->tv_pbuf, tv->tv_zb, tv->tv_dnp, + tv->tv_td->td_arg); } - return (err != 0 ? err : lasterr); + return (tv->tv_err != 0 ? tv->tv_err : tv->tv_lasterr); +} + +/* + * Due to limited stack space recursive functions are frowned upon in + * the Linux kernel. However, they often are the most elegant solution + * to a problem. The following code preserves the recursive function + * traverse_visitbp() 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 16 levels of recursion. + * This change does ugly-up-the-code but it reduces the worst case + * usage from roughly 2496 bytes to 576 bytes on x86_64 archs. + */ +static int +traverse_visitbp(struct traverse_data *td, const dnode_phys_t *dnp, + arc_buf_t *pbuf, blkptr_t *bp, const zbookmark_t *zb) +{ + struct traverse_visitbp_data *tv; + int error; + + tv = kmem_zalloc(sizeof(struct traverse_visitbp_data) * + TRAVERSE_VISITBP_MAX_DEPTH, KM_SLEEP); + __traverse_visitbp_init(tv, td, dnp, pbuf, bp, zb, 0); + + error = __traverse_visitbp(tv); + + kmem_free(tv, sizeof(struct traverse_visitbp_data) * + TRAVERSE_VISITBP_MAX_DEPTH); + + return (error); } static int