On Fri, Mar 24, 2023 at 08:10:31PM +0100, Wysocki, Rafael J wrote: > On 3/24/2023 1:19 AM, Paul E. McKenney wrote: > > The current srcu_struct structure is on the order of 200 bytes in size > > (depending on architecture and .config), which is much better than the > > old-style 26K bytes, but still all too inconvenient when one is trying > > to achieve good cache locality on a fastpath involving SRCU readers. > > > > However, only a few fields in srcu_struct are used by SRCU readers. > > The remaining fields could be offloaded to a new srcu_update > > structure, thus shrinking the srcu_struct structure down to a few > > tens of bytes. This commit begins this noble quest, a quest that is > > complicated by open-coded initialization of the srcu_struct within the > > srcu_notifier_head structure. This complication is addressed by updating > > the srcu_notifier_head structure's open coding, given that there does > > not appear to be a straightforward way of abstracting that initialization. > > > > This commit moves only the ->node pointer to srcu_update. Later commits > > will move additional fields. > > > > [ paulmck: Fold in qiang1.zhang@xxxxxxxxx's memory-leak fix. ] > > > > Link: https://lore.kernel.org/all/20230320055751.4120251-1-qiang1.zhang@xxxxxxxxx/ > > Suggested-by: Christoph Hellwig <hch@xxxxxx> > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > Cc: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx> > > Cc: "Michał Mirosław" <mirq-linux@xxxxxxxxxxxx> > > Cc: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> > > Fine with me. > > Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> Thank you! I will add this on my next rebase. It is possible that this will be v6.5 rather than v6.4 material. Thanx, Paul > > --- > > include/linux/notifier.h | 5 ++++- > > include/linux/srcutiny.h | 6 +++--- > > include/linux/srcutree.h | 27 ++++++++++++++++++--------- > > kernel/rcu/rcu.h | 6 ++++-- > > kernel/rcu/srcutree.c | 28 +++++++++++++++++++--------- > > 5 files changed, 48 insertions(+), 24 deletions(-) > > > > diff --git a/include/linux/notifier.h b/include/linux/notifier.h > > index aef88c2d1173..2aba75145144 100644 > > --- a/include/linux/notifier.h > > +++ b/include/linux/notifier.h > > @@ -73,6 +73,9 @@ struct raw_notifier_head { > > struct srcu_notifier_head { > > struct mutex mutex; > > +#ifdef CONFIG_TREE_SRCU > > + struct srcu_usage srcuu; > > +#endif > > struct srcu_struct srcu; > > struct notifier_block __rcu *head; > > }; > > @@ -107,7 +110,7 @@ extern void srcu_init_notifier_head(struct srcu_notifier_head *nh); > > { \ > > .mutex = __MUTEX_INITIALIZER(name.mutex), \ > > .head = NULL, \ > > - .srcu = __SRCU_STRUCT_INIT(name.srcu, pcpu), \ > > + .srcu = __SRCU_STRUCT_INIT(name.srcu, name.srcuu, pcpu), \ > > } > > #define ATOMIC_NOTIFIER_HEAD(name) \ > > diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h > > index 5aa5e0faf6a1..ebd72491af99 100644 > > --- a/include/linux/srcutiny.h > > +++ b/include/linux/srcutiny.h > > @@ -31,7 +31,7 @@ struct srcu_struct { > > void srcu_drive_gp(struct work_struct *wp); > > -#define __SRCU_STRUCT_INIT(name, __ignored) \ > > +#define __SRCU_STRUCT_INIT(name, __ignored, ___ignored) \ > > { \ > > .srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq), \ > > .srcu_cb_tail = &name.srcu_cb_head, \ > > @@ -44,9 +44,9 @@ void srcu_drive_gp(struct work_struct *wp); > > * Tree SRCU, which needs some per-CPU data. > > */ > > #define DEFINE_SRCU(name) \ > > - struct srcu_struct name = __SRCU_STRUCT_INIT(name, name) > > + struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name) > > #define DEFINE_STATIC_SRCU(name) \ > > - static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name) > > + static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name) > > void synchronize_srcu(struct srcu_struct *ssp); > > diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h > > index 428480152375..2689e64024bb 100644 > > --- a/include/linux/srcutree.h > > +++ b/include/linux/srcutree.h > > @@ -57,11 +57,17 @@ struct srcu_node { > > int grphi; /* Biggest CPU for node. */ > > }; > > +/* > > + * Per-SRCU-domain structure, update-side data linked from srcu_struct. > > + */ > > +struct srcu_usage { > > + struct srcu_node *node; /* Combining tree. */ > > +}; > > + > > /* > > * Per-SRCU-domain structure, similar in function to rcu_state. > > */ > > struct srcu_struct { > > - struct srcu_node *node; /* Combining tree. */ > > struct srcu_node *level[RCU_NUM_LVLS + 1]; > > /* First node at each level. */ > > int srcu_size_state; /* Small-to-big transition state. */ > > @@ -90,6 +96,7 @@ struct srcu_struct { > > unsigned long reschedule_count; > > struct delayed_work work; > > struct lockdep_map dep_map; > > + struct srcu_usage *srcu_sup; /* Update-side data. */ > > }; > > // Values for size state variable (->srcu_size_state). Once the state > > @@ -121,24 +128,24 @@ struct srcu_struct { > > #define SRCU_STATE_SCAN1 1 > > #define SRCU_STATE_SCAN2 2 > > -#define __SRCU_STRUCT_INIT_COMMON(name) \ > > +#define __SRCU_STRUCT_INIT_COMMON(name, usage_name) \ > > .lock = __SPIN_LOCK_UNLOCKED(name.lock), \ > > .srcu_gp_seq_needed = -1UL, \ > > .work = __DELAYED_WORK_INITIALIZER(name.work, NULL, 0), \ > > + .srcu_sup = &usage_name, \ > > __SRCU_DEP_MAP_INIT(name) > > -#define __SRCU_STRUCT_INIT_MODULE(name) \ > > +#define __SRCU_STRUCT_INIT_MODULE(name, usage_name) \ > > { \ > > - __SRCU_STRUCT_INIT_COMMON(name) \ > > + __SRCU_STRUCT_INIT_COMMON(name, usage_name) \ > > } > > -#define __SRCU_STRUCT_INIT(name, pcpu_name) \ > > +#define __SRCU_STRUCT_INIT(name, usage_name, pcpu_name) \ > > { \ > > .sda = &pcpu_name, \ > > - __SRCU_STRUCT_INIT_COMMON(name) \ > > + __SRCU_STRUCT_INIT_COMMON(name, usage_name) \ > > } > > - > > /* > > * Define and initialize a srcu struct at build time. > > * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it. > > @@ -160,15 +167,17 @@ struct srcu_struct { > > */ > > #ifdef MODULE > > # define __DEFINE_SRCU(name, is_static) \ > > - is_static struct srcu_struct name = __SRCU_STRUCT_INIT_MODULE(name); \ > > + static struct srcu_usage name##_srcu_usage; \ > > + is_static struct srcu_struct name = __SRCU_STRUCT_INIT_MODULE(name, name##_srcu_usage); \ > > extern struct srcu_struct * const __srcu_struct_##name; \ > > struct srcu_struct * const __srcu_struct_##name \ > > __section("___srcu_struct_ptrs") = &name > > #else > > # define __DEFINE_SRCU(name, is_static) \ > > static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data); \ > > + static struct srcu_usage name##_srcu_usage; \ > > is_static struct srcu_struct name = \ > > - __SRCU_STRUCT_INIT(name, name##_srcu_data) > > + __SRCU_STRUCT_INIT(name, name##_srcu_usage, name##_srcu_data) > > #endif > > #define DEFINE_SRCU(name) __DEFINE_SRCU(name, /* not static */) > > #define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, static) > > diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h > > index a3adcf9a9919..4a1b9622598b 100644 > > --- a/kernel/rcu/rcu.h > > +++ b/kernel/rcu/rcu.h > > @@ -378,11 +378,13 @@ extern void rcu_init_geometry(void); > > * specified state structure (for SRCU) or the only rcu_state structure > > * (for RCU). > > */ > > -#define srcu_for_each_node_breadth_first(sp, rnp) \ > > +#define _rcu_for_each_node_breadth_first(sp, rnp) \ > > for ((rnp) = &(sp)->node[0]; \ > > (rnp) < &(sp)->node[rcu_num_nodes]; (rnp)++) > > #define rcu_for_each_node_breadth_first(rnp) \ > > - srcu_for_each_node_breadth_first(&rcu_state, rnp) > > + _rcu_for_each_node_breadth_first(&rcu_state, rnp) > > +#define srcu_for_each_node_breadth_first(ssp, rnp) \ > > + _rcu_for_each_node_breadth_first(ssp->srcu_sup, rnp) > > /* > > * Scan the leaves of the rcu_node hierarchy for the rcu_state structure. > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > > index 7a6d9452a5d0..ad1d5ca42a99 100644 > > --- a/kernel/rcu/srcutree.c > > +++ b/kernel/rcu/srcutree.c > > @@ -173,12 +173,12 @@ static bool init_srcu_struct_nodes(struct srcu_struct *ssp, gfp_t gfp_flags) > > /* Initialize geometry if it has not already been initialized. */ > > rcu_init_geometry(); > > - ssp->node = kcalloc(rcu_num_nodes, sizeof(*ssp->node), gfp_flags); > > - if (!ssp->node) > > + ssp->srcu_sup->node = kcalloc(rcu_num_nodes, sizeof(*ssp->srcu_sup->node), gfp_flags); > > + if (!ssp->srcu_sup->node) > > return false; > > /* Work out the overall tree geometry. */ > > - ssp->level[0] = &ssp->node[0]; > > + ssp->level[0] = &ssp->srcu_sup->node[0]; > > for (i = 1; i < rcu_num_lvls; i++) > > ssp->level[i] = ssp->level[i - 1] + num_rcu_lvl[i - 1]; > > rcu_init_levelspread(levelspread, num_rcu_lvl); > > @@ -195,7 +195,7 @@ static bool init_srcu_struct_nodes(struct srcu_struct *ssp, gfp_t gfp_flags) > > snp->srcu_gp_seq_needed_exp = SRCU_SNP_INIT_SEQ; > > snp->grplo = -1; > > snp->grphi = -1; > > - if (snp == &ssp->node[0]) { > > + if (snp == &ssp->srcu_sup->node[0]) { > > /* Root node, special case. */ > > snp->srcu_parent = NULL; > > continue; > > @@ -236,8 +236,12 @@ static bool init_srcu_struct_nodes(struct srcu_struct *ssp, gfp_t gfp_flags) > > */ > > static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static) > > { > > + if (!is_static) > > + ssp->srcu_sup = kzalloc(sizeof(*ssp->srcu_sup), GFP_KERNEL); > > + if (!ssp->srcu_sup) > > + return -ENOMEM; > > ssp->srcu_size_state = SRCU_SIZE_SMALL; > > - ssp->node = NULL; > > + ssp->srcu_sup->node = NULL; > > mutex_init(&ssp->srcu_cb_mutex); > > mutex_init(&ssp->srcu_gp_mutex); > > ssp->srcu_idx = 0; > > @@ -249,8 +253,11 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static) > > ssp->sda_is_static = is_static; > > if (!is_static) > > ssp->sda = alloc_percpu(struct srcu_data); > > - if (!ssp->sda) > > + if (!ssp->sda) { > > + if (!is_static) > > + kfree(ssp->srcu_sup); > > return -ENOMEM; > > + } > > init_srcu_struct_data(ssp); > > ssp->srcu_gp_seq_needed_exp = 0; > > ssp->srcu_last_gp_end = ktime_get_mono_fast_ns(); > > @@ -259,6 +266,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static) > > if (!ssp->sda_is_static) { > > free_percpu(ssp->sda); > > ssp->sda = NULL; > > + kfree(ssp->srcu_sup); > > return -ENOMEM; > > } > > } else { > > @@ -656,13 +664,15 @@ void cleanup_srcu_struct(struct srcu_struct *ssp) > > rcu_seq_current(&ssp->srcu_gp_seq), ssp->srcu_gp_seq_needed); > > return; /* Caller forgot to stop doing call_srcu()? */ > > } > > + kfree(ssp->srcu_sup->node); > > + ssp->srcu_sup->node = NULL; > > + ssp->srcu_size_state = SRCU_SIZE_SMALL; > > if (!ssp->sda_is_static) { > > free_percpu(ssp->sda); > > ssp->sda = NULL; > > + kfree(ssp->srcu_sup); > > + ssp->srcu_sup = NULL; > > } > > - kfree(ssp->node); > > - ssp->node = NULL; > > - ssp->srcu_size_state = SRCU_SIZE_SMALL; > > } > > EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
