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Fri, 04 Sep 2026 04:05:22 -0700 (PDT) From: Bo Zhang To: aliceryhl@google.com, gregkh@linuxfoundation.org, cmllamas@google.com Cc: arve@android.com, tkjos@android.com, christian@brauner.io, surenb@google.com, baohua@kernel.org, zhanghongru06@gmail.com, linux-kernel@vger.kernel.org, Bo Zhang Subject: [RFC PATCH v3 1/2] binder: switch alloc->mutex to spinlock for buffer metadata Date: Fri, 4 Sep 2026 19:04:47 +0800 Message-Id: <20260904110448.23086-2-zhangbo0325@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260904110448.23086-1-zhangbo0325@gmail.com> References: <20260904110448.23086-1-zhangbo0325@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Bo Zhang The alloc->mutex is a highly contended lock on Android devices. When a low-priority task holds this mutex and sleeps, high-priority binder transactions are blocked, causing priority inversion and latency spikes. Split the lock by converting alloc->mutex to a spinlock that only protects buffer metadata. This eliminates the sleeping and priority inversion on the hot path. Page installation and shrinker zap serialization is handled separately by a dedicated install_mutex introduced in the next patch. Performance (binderThroughputTest, SM8850, 2 workers, 10 runs): mutex spinlock throughput: 27k-59k iter/s 79k-84k iter/s average: 0.031-0.068ms 0.022-0.023ms P99: 0.088-0.148ms 0.050-0.062ms Signed-off-by: Bo Zhang --- drivers/android/binder_alloc.c | 36 +++++++++++++++++----------------- drivers/android/binder_alloc.h | 8 ++++---- 2 files changed, 22 insertions(+), 22 deletions(-) diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c index e4488ad86a65..9775df3616aa 100644 --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -169,7 +169,7 @@ static struct binder_buffer *binder_alloc_prepare_to_free_locked( struct binder_buffer *binder_alloc_prepare_to_free(struct binder_alloc *alloc, unsigned long user_ptr) { - guard(mutex)(&alloc->mutex); + guard(spinlock)(&alloc->lock); return binder_alloc_prepare_to_free_locked(alloc, user_ptr); } @@ -676,10 +676,10 @@ struct binder_buffer *binder_alloc_new_buf(struct binder_alloc *alloc, if (!next) return ERR_PTR(-ENOMEM); - mutex_lock(&alloc->mutex); + spin_lock(&alloc->lock); buffer = binder_alloc_new_buf_locked(alloc, next, size, is_async); if (IS_ERR(buffer)) { - mutex_unlock(&alloc->mutex); + spin_unlock(&alloc->lock); goto out; } @@ -687,7 +687,7 @@ struct binder_buffer *binder_alloc_new_buf(struct binder_alloc *alloc, buffer->offsets_size = offsets_size; buffer->extra_buffers_size = extra_buffers_size; buffer->pid = current->tgid; - mutex_unlock(&alloc->mutex); + spin_unlock(&alloc->lock); ret = binder_install_buffer_pages(alloc, buffer, size); if (ret) { @@ -872,9 +872,9 @@ void binder_alloc_free_buf(struct binder_alloc *alloc, binder_alloc_clear_buf(alloc, buffer); buffer->clear_on_free = false; } - mutex_lock(&alloc->mutex); + spin_lock(&alloc->lock); binder_free_buf_locked(alloc, buffer); - mutex_unlock(&alloc->mutex); + spin_unlock(&alloc->lock); } EXPORT_SYMBOL_IF_KUNIT(binder_alloc_free_buf); @@ -967,7 +967,7 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc) struct binder_buffer *buffer; buffers = 0; - mutex_lock(&alloc->mutex); + spin_lock(&alloc->lock); BUG_ON(alloc->mapped); while ((n = rb_first(&alloc->allocated_buffers))) { @@ -1018,7 +1018,7 @@ void binder_alloc_deferred_release(struct binder_alloc *alloc) page_count++; } } - mutex_unlock(&alloc->mutex); + spin_unlock(&alloc->lock); kvfree(alloc->pages); if (alloc->mm) mmdrop(alloc->mm); @@ -1043,7 +1043,7 @@ void binder_alloc_print_allocated(struct seq_file *m, struct binder_buffer *buffer; struct rb_node *n; - guard(mutex)(&alloc->mutex); + guard(spinlock)(&alloc->lock); for (n = rb_first(&alloc->allocated_buffers); n; n = rb_next(n)) { buffer = rb_entry(n, struct binder_buffer, rb_node); seq_printf(m, " buffer %d: %lx size %zd:%zd:%zd %s\n", @@ -1069,7 +1069,7 @@ void binder_alloc_print_pages(struct seq_file *m, int lru = 0; int free = 0; - mutex_lock(&alloc->mutex); + spin_lock(&alloc->lock); /* * Make sure the binder_alloc is fully initialized, otherwise we might * read inconsistent state. @@ -1085,7 +1085,7 @@ void binder_alloc_print_pages(struct seq_file *m, lru++; } } - mutex_unlock(&alloc->mutex); + spin_unlock(&alloc->lock); seq_printf(m, " pages: %d:%d:%d\n", active, lru, free); seq_printf(m, " pages high watermark: %zu\n", alloc->pages_high); } @@ -1101,7 +1101,7 @@ int binder_alloc_get_allocated_count(struct binder_alloc *alloc) struct rb_node *n; int count = 0; - guard(mutex)(&alloc->mutex); + guard(spinlock)(&alloc->lock); for (n = rb_first(&alloc->allocated_buffers); n != NULL; n = rb_next(n)) count++; return count; @@ -1161,8 +1161,8 @@ enum lru_status binder_alloc_free_page(struct list_head *item, vma = vma_lookup(mm, page_addr); } - if (!mutex_trylock(&alloc->mutex)) - goto err_get_alloc_mutex_failed; + if (!spin_trylock(&alloc->lock)) + goto err_get_alloc_lock_failed; /* * Since a binder_alloc can only be mapped once, we ensure @@ -1180,6 +1180,7 @@ enum lru_status binder_alloc_free_page(struct list_head *item, trace_binder_unmap_kernel_end(alloc, index); list_lru_isolate(lru, item); + spin_unlock(&alloc->lock); spin_unlock(&lru->lock); if (vma) { @@ -1190,7 +1191,6 @@ enum lru_status binder_alloc_free_page(struct list_head *item, trace_binder_unmap_user_end(alloc, index); } - mutex_unlock(&alloc->mutex); if (mm_locked) mmap_read_unlock(mm); else @@ -1201,8 +1201,8 @@ enum lru_status binder_alloc_free_page(struct list_head *item, return LRU_REMOVED_RETRY; err_invalid_vma: - mutex_unlock(&alloc->mutex); -err_get_alloc_mutex_failed: + spin_unlock(&alloc->lock); +err_get_alloc_lock_failed: if (mm_locked) mmap_read_unlock(mm); else @@ -1235,7 +1235,7 @@ VISIBLE_IF_KUNIT void __binder_alloc_init(struct binder_alloc *alloc, alloc->pid = current->tgid; alloc->mm = current->mm; mmgrab(alloc->mm); - mutex_init(&alloc->mutex); + spin_lock_init(&alloc->lock); INIT_LIST_HEAD(&alloc->buffers); alloc->freelist = freelist; } diff --git a/drivers/android/binder_alloc.h b/drivers/android/binder_alloc.h index d6f1f6f2d00e..bea5a77bb6da 100644 --- a/drivers/android/binder_alloc.h +++ b/drivers/android/binder_alloc.h @@ -9,7 +9,7 @@ #include #include #include -#include +#include #include #include #include @@ -80,7 +80,7 @@ static inline struct list_head *page_to_lru(struct page *p) /** * struct binder_alloc - per-binder proc state for binder allocator - * @mutex: protects binder_alloc fields + * @lock: protects binder_alloc fields * @mm: copy of task->mm (invariant after open) * @vm_start: base of per-proc address space mapped via mmap * @buffers: list of all buffers for this proc @@ -105,7 +105,7 @@ static inline struct list_head *page_to_lru(struct page *p) * struct binder_buffer objects used to track the user buffers */ struct binder_alloc { - struct mutex mutex; + spinlock_t lock; struct mm_struct *mm; unsigned long vm_start; struct list_head buffers; @@ -156,7 +156,7 @@ void binder_alloc_print_pages(struct seq_file *m, static inline size_t binder_alloc_get_free_async_space(struct binder_alloc *alloc) { - guard(mutex)(&alloc->mutex); + guard(spinlock)(&alloc->lock); return alloc->free_async_space; } -- 2.34.1