ANDROID: binder: always allocate/map first BINDER_MIN_ALLOC pages

Certain usecases like camera are constantly allocating and freeing
binder buffers beyond the first 4k resulting in mmap_sem contention.

If we expand the allocated range from 4k to something higher, we can
reduce the contention. Tests show that 6 pages is enough to cause very
little update_page_range operations and reduces contention.

Bug: 36727951

Change-Id: I28bc3fb9b33c764c257e28487712fce2a3c1078b
Reported-by: Tim Murray <timmurray@google.com>
Signed-off-by: Joel Fernandes <joelaf@google.com>

Pre-allocate 1 instead of 6 pages as in the original patch,
as we use this pre-allocated page to prevent the first page
from getting unpinned after removing the buffer headers,
rather than pinning pages to speedup larger transactions.

Change-Id: Id027adcfd61b2d6b37f69a3f6009a068e90e84f0
Signed-off-by: Sherry Yang <sherryy@android.com>

1 files changed, 27 insertions, 3 deletions

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 0a541fee6784..f0f17799b5af 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -30,6 +30,8 @@
 #include "binder_alloc.h"
 #include "binder_trace.h"
 
+#define BINDER_MIN_ALLOC (1 * PAGE_SIZE)
+
 static DEFINE_MUTEX(binder_alloc_mmap_lock);
 
 enum {
@@ -182,9 +184,9 @@ struct binder_buffer *binder_alloc_prepare_to_free(struct binder_alloc *alloc,
 	return buffer;
 }
 
-static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
-				    void *start, void *end,
-				    struct vm_area_struct *vma)
+static int __binder_update_page_range(struct binder_alloc *alloc, int allocate,
+				      void *start, void *end,
+				      struct vm_area_struct *vma)
 {
 	void *page_addr;
 	unsigned long user_page_addr;
@@ -284,6 +286,20 @@ err_no_vma:
 	return vma ? -ENOMEM : -ESRCH;
 }
 
+static int binder_update_page_range(struct binder_alloc *alloc, int allocate,
+				    void *start, void *end,
+				    struct vm_area_struct *vma)
+{
+	/*
+	 * For regular updates, move up start if needed since MIN_ALLOC pages
+	 * are always mapped
+	 */
+	if (start - alloc->buffer < BINDER_MIN_ALLOC)
+		start = alloc->buffer + BINDER_MIN_ALLOC;
+
+	return __binder_update_page_range(alloc, allocate, start, end, vma);
+}
+
 struct binder_buffer *binder_alloc_new_buf_locked(struct binder_alloc *alloc,
 						  size_t data_size,
 						  size_t offsets_size,
@@ -667,6 +683,12 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
 		goto err_alloc_buf_struct_failed;
 	}
 
+	if (__binder_update_page_range(alloc, 1, alloc->buffer,
+				       alloc->buffer + BINDER_MIN_ALLOC, vma)) {
+		ret = -ENOMEM;
+		failure_string = "alloc small buf";
+		goto err_alloc_small_buf_failed;
+	}
 	buffer->data = alloc->buffer;
 	list_add(&buffer->entry, &alloc->buffers);
 	buffer->free = 1;
@@ -678,6 +700,8 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
 
 	return 0;
 
+err_alloc_small_buf_failed:
+	kfree(buffer);
 err_alloc_buf_struct_failed:
 	kfree(alloc->pages);
 	alloc->pages = NULL;