On Tue, Mar 19, 2024 at 03:14:07PM +0000, Daniel P. Berrangé wrote: > Sending this PULL feels little rushed, as I still have > un-answered questions on the inital patch posting just > a few hours ago....
Sorry, I hadn't seen your email. I'll update this email thread once the discussion has finished. Stefan > > On Tue, Mar 19, 2024 at 11:09:38AM -0400, Stefan Hajnoczi wrote: > > The coroutine pool implementation can hit the Linux vm.max_map_count > > limit, causing QEMU to abort with "failed to allocate memory for stack" > > or "failed to set up stack guard page" during coroutine creation. > > > > This happens because per-thread pools can grow to tens of thousands of > > coroutines. Each coroutine causes 2 virtual memory areas to be created. > > Eventually vm.max_map_count is reached and memory-related syscalls fail. > > The per-thread pool sizes are non-uniform and depend on past coroutine > > usage in each thread, so it's possible for one thread to have a large > > pool while another thread's pool is empty. > > > > Switch to a new coroutine pool implementation with a global pool that > > grows to a maximum number of coroutines and per-thread local pools that > > are capped at hardcoded small number of coroutines. > > > > This approach does not leave large numbers of coroutines pooled in a > > thread that may not use them again. In order to perform well it > > amortizes the cost of global pool accesses by working in batches of > > coroutines instead of individual coroutines. > > > > The global pool is a list. Threads donate batches of coroutines to when > > they have too many and take batches from when they have too few: > > > > .-----------------------------------. > > | Batch 1 | Batch 2 | Batch 3 | ... | global_pool > > `-----------------------------------' > > > > Each thread has up to 2 batches of coroutines: > > > > .-------------------. > > | Batch 1 | Batch 2 | per-thread local_pool (maximum 2 batches) > > `-------------------' > > > > The goal of this change is to reduce the excessive number of pooled > > coroutines that cause QEMU to abort when vm.max_map_count is reached > > without losing the performance of an adequately sized coroutine pool. > > > > Here are virtio-blk disk I/O benchmark results: > > > > RW BLKSIZE IODEPTH OLD NEW CHANGE > > randread 4k 1 113725 117451 +3.3% > > randread 4k 8 192968 198510 +2.9% > > randread 4k 16 207138 209429 +1.1% > > randread 4k 32 212399 215145 +1.3% > > randread 4k 64 218319 221277 +1.4% > > randread 128k 1 17587 17535 -0.3% > > randread 128k 8 17614 17616 +0.0% > > randread 128k 16 17608 17609 +0.0% > > randread 128k 32 17552 17553 +0.0% > > randread 128k 64 17484 17484 +0.0% > > > > See files/{fio.sh,test.xml.j2} for the benchmark configuration: > > https://gitlab.com/stefanha/virt-playbooks/-/tree/coroutine-pool-fix-sizing > > > > Buglink: https://issues.redhat.com/browse/RHEL-28947 > > Reported-by: Sanjay Rao <s...@redhat.com> > > Reported-by: Boaz Ben Shabat <bbens...@redhat.com> > > Reported-by: Joe Mario <jma...@redhat.com> > > Reviewed-by: Kevin Wolf <kw...@redhat.com> > > Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com> > > Message-ID: <20240318183429.1039340-1-stefa...@redhat.com> > > --- > > util/qemu-coroutine.c | 282 +++++++++++++++++++++++++++++++++--------- > > 1 file changed, 223 insertions(+), 59 deletions(-) > > > > diff --git a/util/qemu-coroutine.c b/util/qemu-coroutine.c > > index 5fd2dbaf8b..2790959eaf 100644 > > --- a/util/qemu-coroutine.c > > +++ b/util/qemu-coroutine.c > > @@ -18,39 +18,200 @@ > > #include "qemu/atomic.h" > > #include "qemu/coroutine_int.h" > > #include "qemu/coroutine-tls.h" > > +#include "qemu/cutils.h" > > #include "block/aio.h" > > > > -/** > > - * The minimal batch size is always 64, coroutines from the release_pool > > are > > - * reused as soon as there are 64 coroutines in it. The maximum pool size > > starts > > - * with 64 and is increased on demand so that coroutines are not deleted > > even if > > - * they are not immediately reused. > > - */ > > enum { > > - POOL_MIN_BATCH_SIZE = 64, > > - POOL_INITIAL_MAX_SIZE = 64, > > + COROUTINE_POOL_BATCH_MAX_SIZE = 128, > > }; > > > > -/** Free list to speed up creation */ > > -static QSLIST_HEAD(, Coroutine) release_pool = > > QSLIST_HEAD_INITIALIZER(pool); > > -static unsigned int pool_max_size = POOL_INITIAL_MAX_SIZE; > > -static unsigned int release_pool_size; > > +/* > > + * Coroutine creation and deletion is expensive so a pool of unused > > coroutines > > + * is kept as a cache. When the pool has coroutines available, they are > > + * recycled instead of creating new ones from scratch. Coroutines are > > added to > > + * the pool upon termination. > > + * > > + * The pool is global but each thread maintains a small local pool to avoid > > + * global pool contention. Threads fetch and return batches of coroutines > > from > > + * the global pool to maintain their local pool. The local pool holds up > > to two > > + * batches whereas the maximum size of the global pool is controlled by the > > + * qemu_coroutine_inc_pool_size() API. > > + * > > + * .-----------------------------------. > > + * | Batch 1 | Batch 2 | Batch 3 | ... | global_pool > > + * `-----------------------------------' > > + * > > + * .-------------------. > > + * | Batch 1 | Batch 2 | per-thread local_pool (maximum 2 batches) > > + * `-------------------' > > + */ > > +typedef struct CoroutinePoolBatch { > > + /* Batches are kept in a list */ > > + QSLIST_ENTRY(CoroutinePoolBatch) next; > > > > -typedef QSLIST_HEAD(, Coroutine) CoroutineQSList; > > -QEMU_DEFINE_STATIC_CO_TLS(CoroutineQSList, alloc_pool); > > -QEMU_DEFINE_STATIC_CO_TLS(unsigned int, alloc_pool_size); > > -QEMU_DEFINE_STATIC_CO_TLS(Notifier, coroutine_pool_cleanup_notifier); > > + /* This batch holds up to @COROUTINE_POOL_BATCH_MAX_SIZE coroutines */ > > + QSLIST_HEAD(, Coroutine) list; > > + unsigned int size; > > +} CoroutinePoolBatch; > > > > -static void coroutine_pool_cleanup(Notifier *n, void *value) > > +typedef QSLIST_HEAD(, CoroutinePoolBatch) CoroutinePool; > > + > > +/* Host operating system limit on number of pooled coroutines */ > > +static unsigned int global_pool_hard_max_size; > > + > > +static QemuMutex global_pool_lock; /* protects the following variables */ > > +static CoroutinePool global_pool = QSLIST_HEAD_INITIALIZER(global_pool); > > +static unsigned int global_pool_size; > > +static unsigned int global_pool_max_size = COROUTINE_POOL_BATCH_MAX_SIZE; > > + > > +QEMU_DEFINE_STATIC_CO_TLS(CoroutinePool, local_pool); > > +QEMU_DEFINE_STATIC_CO_TLS(Notifier, local_pool_cleanup_notifier); > > + > > +static CoroutinePoolBatch *coroutine_pool_batch_new(void) > > +{ > > + CoroutinePoolBatch *batch = g_new(CoroutinePoolBatch, 1); > > + > > + QSLIST_INIT(&batch->list); > > + batch->size = 0; > > + return batch; > > +} > > + > > +static void coroutine_pool_batch_delete(CoroutinePoolBatch *batch) > > { > > Coroutine *co; > > Coroutine *tmp; > > - CoroutineQSList *alloc_pool = get_ptr_alloc_pool(); > > > > - QSLIST_FOREACH_SAFE(co, alloc_pool, pool_next, tmp) { > > - QSLIST_REMOVE_HEAD(alloc_pool, pool_next); > > + QSLIST_FOREACH_SAFE(co, &batch->list, pool_next, tmp) { > > + QSLIST_REMOVE_HEAD(&batch->list, pool_next); > > qemu_coroutine_delete(co); > > } > > + g_free(batch); > > +} > > + > > +static void local_pool_cleanup(Notifier *n, void *value) > > +{ > > + CoroutinePool *local_pool = get_ptr_local_pool(); > > + CoroutinePoolBatch *batch; > > + CoroutinePoolBatch *tmp; > > + > > + QSLIST_FOREACH_SAFE(batch, local_pool, next, tmp) { > > + QSLIST_REMOVE_HEAD(local_pool, next); > > + coroutine_pool_batch_delete(batch); > > + } > > +} > > + > > +/* Ensure the atexit notifier is registered */ > > +static void local_pool_cleanup_init_once(void) > > +{ > > + Notifier *notifier = get_ptr_local_pool_cleanup_notifier(); > > + if (!notifier->notify) { > > + notifier->notify = local_pool_cleanup; > > + qemu_thread_atexit_add(notifier); > > + } > > +} > > + > > +/* Helper to get the next unused coroutine from the local pool */ > > +static Coroutine *coroutine_pool_get_local(void) > > +{ > > + CoroutinePool *local_pool = get_ptr_local_pool(); > > + CoroutinePoolBatch *batch = QSLIST_FIRST(local_pool); > > + Coroutine *co; > > + > > + if (unlikely(!batch)) { > > + return NULL; > > + } > > + > > + co = QSLIST_FIRST(&batch->list); > > + QSLIST_REMOVE_HEAD(&batch->list, pool_next); > > + batch->size--; > > + > > + if (batch->size == 0) { > > + QSLIST_REMOVE_HEAD(local_pool, next); > > + coroutine_pool_batch_delete(batch); > > + } > > + return co; > > +} > > + > > +/* Get the next batch from the global pool */ > > +static void coroutine_pool_refill_local(void) > > +{ > > + CoroutinePool *local_pool = get_ptr_local_pool(); > > + CoroutinePoolBatch *batch; > > + > > + WITH_QEMU_LOCK_GUARD(&global_pool_lock) { > > + batch = QSLIST_FIRST(&global_pool); > > + > > + if (batch) { > > + QSLIST_REMOVE_HEAD(&global_pool, next); > > + global_pool_size -= batch->size; > > + } > > + } > > + > > + if (batch) { > > + QSLIST_INSERT_HEAD(local_pool, batch, next); > > + local_pool_cleanup_init_once(); > > + } > > +} > > + > > +/* Add a batch of coroutines to the global pool */ > > +static void coroutine_pool_put_global(CoroutinePoolBatch *batch) > > +{ > > + WITH_QEMU_LOCK_GUARD(&global_pool_lock) { > > + unsigned int max = MIN(global_pool_max_size, > > + global_pool_hard_max_size); > > + > > + if (global_pool_size < max) { > > + QSLIST_INSERT_HEAD(&global_pool, batch, next); > > + > > + /* Overshooting the max pool size is allowed */ > > + global_pool_size += batch->size; > > + return; > > + } > > + } > > + > > + /* The global pool was full, so throw away this batch */ > > + coroutine_pool_batch_delete(batch); > > +} > > + > > +/* Get the next unused coroutine from the pool or return NULL */ > > +static Coroutine *coroutine_pool_get(void) > > +{ > > + Coroutine *co; > > + > > + co = coroutine_pool_get_local(); > > + if (!co) { > > + coroutine_pool_refill_local(); > > + co = coroutine_pool_get_local(); > > + } > > + return co; > > +} > > + > > +static void coroutine_pool_put(Coroutine *co) > > +{ > > + CoroutinePool *local_pool = get_ptr_local_pool(); > > + CoroutinePoolBatch *batch = QSLIST_FIRST(local_pool); > > + > > + if (unlikely(!batch)) { > > + batch = coroutine_pool_batch_new(); > > + QSLIST_INSERT_HEAD(local_pool, batch, next); > > + local_pool_cleanup_init_once(); > > + } > > + > > + if (unlikely(batch->size >= COROUTINE_POOL_BATCH_MAX_SIZE)) { > > + CoroutinePoolBatch *next = QSLIST_NEXT(batch, next); > > + > > + /* Is the local pool full? */ > > + if (next) { > > + QSLIST_REMOVE_HEAD(local_pool, next); > > + coroutine_pool_put_global(batch); > > + } > > + > > + batch = coroutine_pool_batch_new(); > > + QSLIST_INSERT_HEAD(local_pool, batch, next); > > + } > > + > > + QSLIST_INSERT_HEAD(&batch->list, co, pool_next); > > + batch->size++; > > } > > > > Coroutine *qemu_coroutine_create(CoroutineEntry *entry, void *opaque) > > @@ -58,31 +219,7 @@ Coroutine *qemu_coroutine_create(CoroutineEntry *entry, > > void *opaque) > > Coroutine *co = NULL; > > > > if (IS_ENABLED(CONFIG_COROUTINE_POOL)) { > > - CoroutineQSList *alloc_pool = get_ptr_alloc_pool(); > > - > > - co = QSLIST_FIRST(alloc_pool); > > - if (!co) { > > - if (release_pool_size > POOL_MIN_BATCH_SIZE) { > > - /* Slow path; a good place to register the destructor, > > too. */ > > - Notifier *notifier = > > get_ptr_coroutine_pool_cleanup_notifier(); > > - if (!notifier->notify) { > > - notifier->notify = coroutine_pool_cleanup; > > - qemu_thread_atexit_add(notifier); > > - } > > - > > - /* This is not exact; there could be a little skew between > > - * release_pool_size and the actual size of release_pool. > > But > > - * it is just a heuristic, it does not need to be perfect. > > - */ > > - set_alloc_pool_size(qatomic_xchg(&release_pool_size, 0)); > > - QSLIST_MOVE_ATOMIC(alloc_pool, &release_pool); > > - co = QSLIST_FIRST(alloc_pool); > > - } > > - } > > - if (co) { > > - QSLIST_REMOVE_HEAD(alloc_pool, pool_next); > > - set_alloc_pool_size(get_alloc_pool_size() - 1); > > - } > > + co = coroutine_pool_get(); > > } > > > > if (!co) { > > @@ -100,19 +237,10 @@ static void coroutine_delete(Coroutine *co) > > co->caller = NULL; > > > > if (IS_ENABLED(CONFIG_COROUTINE_POOL)) { > > - if (release_pool_size < qatomic_read(&pool_max_size) * 2) { > > - QSLIST_INSERT_HEAD_ATOMIC(&release_pool, co, pool_next); > > - qatomic_inc(&release_pool_size); > > - return; > > - } > > - if (get_alloc_pool_size() < qatomic_read(&pool_max_size)) { > > - QSLIST_INSERT_HEAD(get_ptr_alloc_pool(), co, pool_next); > > - set_alloc_pool_size(get_alloc_pool_size() + 1); > > - return; > > - } > > + coroutine_pool_put(co); > > + } else { > > + qemu_coroutine_delete(co); > > } > > - > > - qemu_coroutine_delete(co); > > } > > > > void qemu_aio_coroutine_enter(AioContext *ctx, Coroutine *co) > > @@ -223,10 +351,46 @@ AioContext *qemu_coroutine_get_aio_context(Coroutine > > *co) > > > > void qemu_coroutine_inc_pool_size(unsigned int additional_pool_size) > > { > > - qatomic_add(&pool_max_size, additional_pool_size); > > + QEMU_LOCK_GUARD(&global_pool_lock); > > + global_pool_max_size += additional_pool_size; > > } > > > > void qemu_coroutine_dec_pool_size(unsigned int removing_pool_size) > > { > > - qatomic_sub(&pool_max_size, removing_pool_size); > > + QEMU_LOCK_GUARD(&global_pool_lock); > > + global_pool_max_size -= removing_pool_size; > > +} > > + > > +static unsigned int get_global_pool_hard_max_size(void) > > +{ > > +#ifdef __linux__ > > + g_autofree char *contents = NULL; > > + int max_map_count; > > + > > + /* > > + * Linux processes can have up to max_map_count virtual memory areas > > + * (VMAs). mmap(2), mprotect(2), etc fail with ENOMEM beyond this > > limit. We > > + * must limit the coroutine pool to a safe size to avoid running out of > > + * VMAs. > > + */ > > + if (g_file_get_contents("/proc/sys/vm/max_map_count", &contents, NULL, > > + NULL) && > > + qemu_strtoi(contents, NULL, 10, &max_map_count) == 0) { > > + /* > > + * This is a conservative upper bound that avoids exceeding > > + * max_map_count. Leave half for non-coroutine users like library > > + * dependencies, vhost-user, etc. Each coroutine takes up 2 VMAs so > > + * halve the amount again. > > + */ > > + return max_map_count / 4; > > + } > > +#endif > > + > > + return UINT_MAX; > > +} > > + > > +static void __attribute__((constructor)) qemu_coroutine_init(void) > > +{ > > + qemu_mutex_init(&global_pool_lock); > > + global_pool_hard_max_size = get_global_pool_hard_max_size(); > > } > > -- > > 2.44.0 > > > > > > With regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| >
signature.asc
Description: PGP signature