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.
This commit is contained in:
Brian Behlendorf
parent
428870ff73
commit
34229a2f2a
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@ -0,0 +1,13 @@
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From: Brian Behlendorf <behlendorf1@llnl.gov>
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Subject: [PATCH] fix stack traverse_visitbp
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Due to limited stack space recursive functions are frowned upon in
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the Linux kernel. However, they often are the most elegant solution
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to a problem. The following code preserves the recursive function
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traverse_visitbp() but moves the local variables AND function
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arguments to the heap to minimize the stack frame size. Enough
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space is initially allocated on the stack for 20 levels of recursion.
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This change does ugly-up-the-code but it reduces the worst case
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usage from roughly 4160 bytes to 960 bytes on x86_64 archs.
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Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
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@ -57,6 +57,33 @@ struct traverse_data {
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void *td_arg;
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void *td_arg;
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};
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};
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struct traverse_visitbp_data {
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/* Function arguments */
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struct traverse_data *tv_td;
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const dnode_phys_t *tv_dnp;
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arc_buf_t *tv_pbuf;
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blkptr_t *tv_bp;
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const zbookmark_t *tv_zb;
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/* Local variables */
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struct prefetch_data *tv_pd;
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zbookmark_t tv_czb;
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arc_buf_t *tv_buf;
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boolean_t tv_hard;
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objset_phys_t *tv_osp;
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dnode_phys_t *tv_ldnp;
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blkptr_t *tv_cbp;
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uint32_t tv_flags;
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int tv_err;
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int tv_lasterr;
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int tv_i;
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int tv_epb;
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#ifdef DEBUG
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int tv_depth;
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#endif
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};
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static inline int traverse_visitbp(struct traverse_data *td, const
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dnode_phys_t *dnp, arc_buf_t *pbuf, blkptr_t *bp, const zbookmark_t *zb);
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static int traverse_dnode(struct traverse_data *td, const dnode_phys_t *dnp,
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static int traverse_dnode(struct traverse_data *td, const dnode_phys_t *dnp,
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arc_buf_t *buf, uint64_t objset, uint64_t object);
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arc_buf_t *buf, uint64_t objset, uint64_t object);
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@ -128,137 +155,191 @@ traverse_zil(struct traverse_data *td, zil_header_t *zh)
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zil_free(zilog);
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zil_free(zilog);
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}
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}
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static int
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#define TRAVERSE_VISITBP_MAX_DEPTH 20
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traverse_visitbp(struct traverse_data *td, const dnode_phys_t *dnp,
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arc_buf_t *pbuf, blkptr_t *bp, const zbookmark_t *zb)
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{
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zbookmark_t czb;
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int err = 0, lasterr = 0;
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arc_buf_t *buf = NULL;
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struct prefetch_data *pd = td->td_pfd;
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boolean_t hard = td->td_flags & TRAVERSE_HARD;
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if (bp->blk_birth == 0) {
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static void
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err = td->td_func(td->td_spa, NULL, NULL, pbuf, zb, dnp,
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__traverse_visitbp_init(struct traverse_visitbp_data *tv,
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td->td_arg);
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struct traverse_data *td, const dnode_phys_t *dnp,
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return (err);
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arc_buf_t *pbuf, blkptr_t *bp, const zbookmark_t *zb, int depth)
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{
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tv->tv_td = td;
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tv->tv_dnp = dnp;
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tv->tv_pbuf = pbuf;
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tv->tv_bp = bp;
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tv->tv_zb = zb;
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tv->tv_err = 0;
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tv->tv_lasterr = 0;
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tv->tv_buf = NULL;
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tv->tv_pd = td->td_pfd;
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tv->tv_hard = td->td_flags & TRAVERSE_HARD;
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tv->tv_flags = ARC_WAIT;
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tv->tv_depth = depth;
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}
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static noinline int
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__traverse_visitbp(struct traverse_visitbp_data *tv)
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{
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ASSERT3S(tv->tv_depth, <, TRAVERSE_VISITBP_MAX_DEPTH);
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if (tv->tv_bp->blk_birth == 0) {
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tv->tv_err = tv->tv_td->td_func(tv->tv_td->td_spa, NULL, NULL,
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tv->tv_pbuf, tv->tv_zb, tv->tv_dnp, tv->tv_td->td_arg);
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return (tv->tv_err);
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}
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}
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if (bp->blk_birth <= td->td_min_txg)
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if (tv->tv_bp->blk_birth <= tv->tv_td->td_min_txg)
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return (0);
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return (0);
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if (pd && !pd->pd_exited &&
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if (tv->tv_pd && !tv->tv_pd->pd_exited &&
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((pd->pd_flags & TRAVERSE_PREFETCH_DATA) ||
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((tv->tv_pd->pd_flags & TRAVERSE_PREFETCH_DATA) ||
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BP_GET_TYPE(bp) == DMU_OT_DNODE || BP_GET_LEVEL(bp) > 0)) {
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BP_GET_TYPE(tv->tv_bp) == DMU_OT_DNODE ||
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mutex_enter(&pd->pd_mtx);
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BP_GET_LEVEL(tv->tv_bp) > 0)) {
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ASSERT(pd->pd_blks_fetched >= 0);
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mutex_enter(&tv->tv_pd->pd_mtx);
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while (pd->pd_blks_fetched == 0 && !pd->pd_exited)
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ASSERT(tv->tv_pd->pd_blks_fetched >= 0);
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cv_wait(&pd->pd_cv, &pd->pd_mtx);
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while (tv->tv_pd->pd_blks_fetched == 0 && !tv->tv_pd->pd_exited)
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pd->pd_blks_fetched--;
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cv_wait(&tv->tv_pd->pd_cv, &tv->tv_pd->pd_mtx);
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cv_broadcast(&pd->pd_cv);
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tv->tv_pd->pd_blks_fetched--;
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mutex_exit(&pd->pd_mtx);
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cv_broadcast(&tv->tv_pd->pd_cv);
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mutex_exit(&tv->tv_pd->pd_mtx);
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}
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}
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if (td->td_flags & TRAVERSE_PRE) {
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if (tv->tv_td->td_flags & TRAVERSE_PRE) {
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err = td->td_func(td->td_spa, NULL, bp, pbuf, zb, dnp,
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tv->tv_err = tv->tv_td->td_func(tv->tv_td->td_spa, NULL,
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td->td_arg);
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tv->tv_bp, tv->tv_pbuf, tv->tv_zb, tv->tv_dnp,
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if (err)
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tv->tv_td->td_arg);
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return (err);
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if (tv->tv_err)
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return (tv->tv_err);
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}
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}
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if (BP_GET_LEVEL(bp) > 0) {
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if (BP_GET_LEVEL(tv->tv_bp) > 0) {
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uint32_t flags = ARC_WAIT;
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tv->tv_epb = BP_GET_LSIZE(tv->tv_bp) >> SPA_BLKPTRSHIFT;
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int i;
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blkptr_t *cbp;
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int epb = BP_GET_LSIZE(bp) >> SPA_BLKPTRSHIFT;
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err = dsl_read(NULL, td->td_spa, bp, pbuf,
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tv->tv_err = dsl_read(NULL, tv->tv_td->td_spa, tv->tv_bp,
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arc_getbuf_func, &buf,
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tv->tv_pbuf, arc_getbuf_func, &tv->tv_buf,
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ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, &flags, zb);
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ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL,
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if (err)
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&tv->tv_flags, tv->tv_zb);
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return (err);
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if (tv->tv_err)
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return (tv->tv_err);
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/* recursively visitbp() blocks below this */
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/* recursively visitbp() blocks below this */
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cbp = buf->b_data;
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tv->tv_cbp = tv->tv_buf->b_data;
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for (i = 0; i < epb; i++, cbp++) {
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for (tv->tv_i = 0; tv->tv_i < tv->tv_epb;
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SET_BOOKMARK(&czb, zb->zb_objset, zb->zb_object,
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tv->tv_i++, tv->tv_cbp++) {
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zb->zb_level - 1,
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SET_BOOKMARK(&tv->tv_czb, tv->tv_zb->zb_objset,
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zb->zb_blkid * epb + i);
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tv->tv_zb->zb_object, tv->tv_zb->zb_level - 1,
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err = traverse_visitbp(td, dnp, buf, cbp, &czb);
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tv->tv_zb->zb_blkid * tv->tv_epb + tv->tv_i);
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if (err) {
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__traverse_visitbp_init(tv + 1, tv->tv_td,
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if (!hard)
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tv->tv_dnp, tv->tv_buf, tv->tv_cbp,
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&tv->tv_czb, tv->tv_depth + 1);
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tv->tv_err = __traverse_visitbp(tv + 1);
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if (tv->tv_err) {
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if (!tv->tv_hard)
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break;
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break;
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lasterr = err;
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tv->tv_lasterr = tv->tv_err;
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}
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}
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}
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}
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} else if (BP_GET_TYPE(bp) == DMU_OT_DNODE) {
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} else if (BP_GET_TYPE(tv->tv_bp) == DMU_OT_DNODE) {
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uint32_t flags = ARC_WAIT;
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tv->tv_epb = BP_GET_LSIZE(tv->tv_bp) >> DNODE_SHIFT;
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int i;
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int epb = BP_GET_LSIZE(bp) >> DNODE_SHIFT;
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err = dsl_read(NULL, td->td_spa, bp, pbuf,
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tv->tv_err = dsl_read(NULL, tv->tv_td->td_spa, tv->tv_bp,
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arc_getbuf_func, &buf,
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tv->tv_pbuf, arc_getbuf_func, &tv->tv_buf,
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ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, &flags, zb);
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ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL,
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if (err)
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&tv->tv_flags, tv->tv_zb);
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return (err);
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if (tv->tv_err)
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return (tv->tv_err);
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/* recursively visitbp() blocks below this */
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/* recursively visitbp() blocks below this */
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dnp = buf->b_data;
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tv->tv_dnp = tv->tv_buf->b_data;
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for (i = 0; i < epb; i++, dnp++) {
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for (tv->tv_i = 0; tv->tv_i < tv->tv_epb;
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err = traverse_dnode(td, dnp, buf, zb->zb_objset,
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tv->tv_i++, tv->tv_dnp++) {
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zb->zb_blkid * epb + i);
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tv->tv_err = traverse_dnode(tv->tv_td, tv->tv_dnp,
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if (err) {
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tv->tv_buf, tv->tv_zb->zb_objset,
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if (!hard)
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tv->tv_zb->zb_blkid * tv->tv_epb + tv->tv_i);
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if (tv->tv_err) {
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if (!tv->tv_hard)
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break;
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break;
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lasterr = err;
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tv->tv_lasterr = tv->tv_err;
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}
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}
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}
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}
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} else if (BP_GET_TYPE(bp) == DMU_OT_OBJSET) {
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} else if (BP_GET_TYPE(tv->tv_bp) == DMU_OT_OBJSET) {
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uint32_t flags = ARC_WAIT;
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objset_phys_t *osp;
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dnode_phys_t *dnp;
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err = dsl_read_nolock(NULL, td->td_spa, bp,
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tv->tv_err = dsl_read_nolock(NULL, tv->tv_td->td_spa,
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arc_getbuf_func, &buf,
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tv->tv_bp, arc_getbuf_func, &tv->tv_buf,
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ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL, &flags, zb);
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ZIO_PRIORITY_ASYNC_READ, ZIO_FLAG_CANFAIL,
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if (err)
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&tv->tv_flags, tv->tv_zb);
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return (err);
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if (tv->tv_err)
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return (tv->tv_err);
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osp = buf->b_data;
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tv->tv_osp = tv->tv_buf->b_data;
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traverse_zil(td, &osp->os_zil_header);
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traverse_zil(tv->tv_td, &tv->tv_osp->os_zil_header);
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dnp = &osp->os_meta_dnode;
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tv->tv_ldnp = &tv->tv_osp->os_meta_dnode;
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err = traverse_dnode(td, dnp, buf, zb->zb_objset,
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tv->tv_err = traverse_dnode(tv->tv_td, tv->tv_ldnp, tv->tv_buf,
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DMU_META_DNODE_OBJECT);
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tv->tv_zb->zb_objset, DMU_META_DNODE_OBJECT);
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if (err && hard) {
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if (tv->tv_err && tv->tv_hard) {
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lasterr = err;
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tv->tv_lasterr = tv->tv_err;
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err = 0;
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tv->tv_err = 0;
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}
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}
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if (err == 0 && arc_buf_size(buf) >= sizeof (objset_phys_t)) {
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if (tv->tv_err == 0 &&
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dnp = &osp->os_userused_dnode;
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arc_buf_size(tv->tv_buf) >= sizeof (objset_phys_t)) {
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err = traverse_dnode(td, dnp, buf, zb->zb_objset,
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tv->tv_ldnp = &tv->tv_osp->os_userused_dnode;
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tv->tv_err = traverse_dnode(tv->tv_td, tv->tv_ldnp,
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tv->tv_buf, tv->tv_zb->zb_objset,
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DMU_USERUSED_OBJECT);
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DMU_USERUSED_OBJECT);
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}
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}
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if (err && hard) {
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if (tv->tv_err && tv->tv_hard) {
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lasterr = err;
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tv->tv_lasterr = tv->tv_err;
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err = 0;
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tv->tv_err = 0;
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}
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}
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if (err == 0 && arc_buf_size(buf) >= sizeof (objset_phys_t)) {
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if (tv->tv_err == 0 &&
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dnp = &osp->os_groupused_dnode;
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arc_buf_size(tv->tv_buf) >= sizeof (objset_phys_t)) {
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err = traverse_dnode(td, dnp, buf, zb->zb_objset,
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tv->tv_ldnp = &tv->tv_osp->os_groupused_dnode;
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tv->tv_err = traverse_dnode(tv->tv_td, tv->tv_ldnp,
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tv->tv_buf, tv->tv_zb->zb_objset,
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DMU_GROUPUSED_OBJECT);
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DMU_GROUPUSED_OBJECT);
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}
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}
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}
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}
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if (buf)
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if (tv->tv_buf)
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(void) arc_buf_remove_ref(buf, &buf);
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(void) arc_buf_remove_ref(tv->tv_buf, &tv->tv_buf);
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if (err == 0 && lasterr == 0 && (td->td_flags & TRAVERSE_POST)) {
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if (tv->tv_err == 0 && tv->tv_lasterr == 0 &&
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err = td->td_func(td->td_spa, NULL, bp, pbuf, zb, dnp,
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(tv->tv_td->td_flags & TRAVERSE_POST)) {
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td->td_arg);
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tv->tv_err = tv->tv_td->td_func(tv->tv_td->td_spa, NULL,
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tv->tv_bp, tv->tv_pbuf, tv->tv_zb, tv->tv_dnp,
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tv->tv_td->td_arg);
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}
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}
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return (err != 0 ? err : lasterr);
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return (tv->tv_err != 0 ? tv->tv_err : tv->tv_lasterr);
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}
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/*
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* Due to limited stack space recursive functions are frowned upon in
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* the Linux kernel. However, they often are the most elegant solution
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* to a problem. The following code preserves the recursive function
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* traverse_visitbp() but moves the local variables AND function
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* arguments to the heap to minimize the stack frame size. Enough
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* space is initially allocated on the stack for 16 levels of recursion.
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* This change does ugly-up-the-code but it reduces the worst case
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* usage from roughly 2496 bytes to 576 bytes on x86_64 archs.
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*/
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static int
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traverse_visitbp(struct traverse_data *td, const dnode_phys_t *dnp,
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arc_buf_t *pbuf, blkptr_t *bp, const zbookmark_t *zb)
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{
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struct traverse_visitbp_data *tv;
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int error;
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tv = kmem_zalloc(sizeof(struct traverse_visitbp_data) *
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TRAVERSE_VISITBP_MAX_DEPTH, KM_SLEEP);
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__traverse_visitbp_init(tv, td, dnp, pbuf, bp, zb, 0);
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error = __traverse_visitbp(tv);
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kmem_free(tv, sizeof(struct traverse_visitbp_data) *
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TRAVERSE_VISITBP_MAX_DEPTH);
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return (error);
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}
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}
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static int
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static int
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Loading…
Reference in New Issue