ion: Add private buffer flag to skip page pooling on free

Currently, when we free a buffer it might actually just go back into a
heap-specific page pool rather than going back to the system. This poses
a problem because sometimes (like when we're running a shrinker in low
memory conditions) we need to force the memory associated with the
buffer to truly be relinquished to the system rather than just going
back into a page pool.

There isn't a use case for this flag by Ion clients, so make it a
private flag. The main use case right now is to provide a mechanism for
the deferred free code to force stale buffers to bypass page pooling.

Change-Id: I724f89cc037083fe8576784363caa18a34e8705a
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>

diff --git a/drivers/staging/android/ion/ion_heap.c b/drivers/staging/android/ion/ion_heap.c
index 5c14bc2a18220b0e9471f5f8a95aff64483694ce..750b76af0cf35dba012a534c74c918bb347f333c 100644 (file)
--- a/drivers/staging/android/ion/ion_heap.c
+++ b/drivers/staging/android/ion/ion_heap.c
@@ -178,7 +178,8 @@ size_t ion_heap_freelist_size(struct ion_heap *heap)
        return size;
 }
 
-size_t ion_heap_freelist_drain(struct ion_heap *heap, size_t size)
+static size_t _ion_heap_freelist_drain(struct ion_heap *heap, size_t size,
+                               bool skip_pools)
 {
        struct ion_buffer *buffer;
        size_t total_drained = 0;
@@ -197,6 +198,8 @@ size_t ion_heap_freelist_drain(struct ion_heap *heap, size_t size)
                                          list);
                list_del(&buffer->list);
                heap->free_list_size -= buffer->size;
+               if (skip_pools)
+                       buffer->private_flags |= ION_PRIV_FLAG_SHRINKER_FREE;
                total_drained += buffer->size;
                spin_unlock(&heap->free_lock);
                ion_buffer_destroy(buffer);
@@ -207,6 +210,16 @@ size_t ion_heap_freelist_drain(struct ion_heap *heap, size_t size)
        return total_drained;
 }
 
+size_t ion_heap_freelist_drain(struct ion_heap *heap, size_t size)
+{
+       return _ion_heap_freelist_drain(heap, size, false);
+}
+
+size_t ion_heap_freelist_shrink(struct ion_heap *heap, size_t size)
+{
+       return _ion_heap_freelist_drain(heap, size, true);
+}
+
 static int ion_heap_deferred_free(void *data)
 {
        struct ion_heap *heap = data;
@@ -265,10 +278,10 @@ static int ion_heap_shrink(struct shrinker *shrinker, struct shrink_control *sc)
 
        /*
         * shrink the free list first, no point in zeroing the memory if we're
-        * just going to reclaim it
+        * just going to reclaim it. Also, skip any possible page pooling.
         */
        if (heap->flags & ION_HEAP_FLAG_DEFER_FREE)
-               freed = ion_heap_freelist_drain(heap, to_scan * PAGE_SIZE) /
+               freed = ion_heap_freelist_shrink(heap, to_scan * PAGE_SIZE) /
                                PAGE_SIZE;
 
        to_scan -= freed;

diff --git a/drivers/staging/android/ion/ion_priv.h b/drivers/staging/android/ion/ion_priv.h
index 85866e6d2f92a9008a8eafa96037cb1962fab358..18ef365e7552ec1b641906f74993c910471bc653 100644 (file)
--- a/drivers/staging/android/ion/ion_priv.h
+++ b/drivers/staging/android/ion/ion_priv.h
@@ -38,6 +38,7 @@ struct ion_buffer *ion_handle_buffer(struct ion_handle *handle);
  * @dev:               back pointer to the ion_device
  * @heap:              back pointer to the heap the buffer came from
  * @flags:             buffer specific flags
+ * @private_flags:     internal buffer specific flags
  * @size:              size of the buffer
  * @priv_virt:         private data to the buffer representable as
  *                     a void *
@@ -66,6 +67,7 @@ struct ion_buffer {
        struct ion_device *dev;
        struct ion_heap *heap;
        unsigned long flags;
+       unsigned long private_flags;
        size_t size;
        union {
                void *priv_virt;
@@ -98,7 +100,11 @@ void ion_buffer_destroy(struct ion_buffer *buffer);
  * @map_user           map memory to userspace
  *
  * allocate, phys, and map_user return 0 on success, -errno on error.
- * map_dma and map_kernel return pointer on success, ERR_PTR on error.
+ * map_dma and map_kernel return pointer on success, ERR_PTR on
+ * error. @free will be called with ION_PRIV_FLAG_SHRINKER_FREE set in
+ * the buffer's private_flags when called from a shrinker. In that
+ * case, the pages being free'd must be truly free'd back to the
+ * system, not put in a page pool or otherwise cached.
  */
 struct ion_heap_ops {
        int (*allocate) (struct ion_heap *heap,
@@ -122,6 +128,17 @@ struct ion_heap_ops {
  */
 #define ION_HEAP_FLAG_DEFER_FREE (1 << 0)
 
+/**
+ * private flags - flags internal to ion
+ */
+/*
+ * Buffer is being freed from a shrinker function. Skip any possible
+ * heap-specific caching mechanism (e.g. page pools). Guarantees that
+ * any buffer storage that came from the system allocator will be
+ * returned to the system allocator.
+ */
+#define ION_PRIV_FLAG_SHRINKER_FREE (1 << 0)
+
 /**
  * struct ion_heap - represents a heap in the system
  * @node:              rb node to put the heap on the device's tree of heaps
@@ -257,6 +274,29 @@ void ion_heap_freelist_add(struct ion_heap *heap, struct ion_buffer *buffer);
  */
 size_t ion_heap_freelist_drain(struct ion_heap *heap, size_t size);
 
+/**
+ * ion_heap_freelist_shrink - drain the deferred free
+ *                             list, skipping any heap-specific
+ *                             pooling or caching mechanisms
+ *
+ * @heap:              the heap
+ * @size:              amount of memory to drain in bytes
+ *
+ * Drains the indicated amount of memory from the deferred freelist immediately.
+ * Returns the total amount freed.  The total freed may be higher depending
+ * on the size of the items in the list, or lower if there is insufficient
+ * total memory on the freelist.
+ *
+ * Unlike with @ion_heap_freelist_drain, don't put any pages back into
+ * page pools or otherwise cache the pages. Everything must be
+ * genuinely free'd back to the system. If you're free'ing from a
+ * shrinker you probably want to use this. Note that this relies on
+ * the heap.ops.free callback honoring the ION_PRIV_FLAG_SHRINKER_FREE
+ * flag.
+ */
+size_t ion_heap_freelist_shrink(struct ion_heap *heap,
+                                       size_t size);
+
 /**
  * ion_heap_freelist_size - returns the size of the freelist in bytes
  * @heap:              the heap

diff --git a/drivers/staging/android/ion/ion_system_heap.c b/drivers/staging/android/ion/ion_system_heap.c
index 4a87fcf53266538e29cf7dcb13fc008be916ea42..a2c8968104f856be71532aeed4c33994641893d4 100644 (file)
--- a/drivers/staging/android/ion/ion_system_heap.c
+++ b/drivers/staging/android/ion/ion_system_heap.c
@@ -90,7 +90,7 @@ static void free_buffer_page(struct ion_system_heap *heap,
 {
        bool cached = ion_buffer_cached(buffer);
 
-       if (!cached) {
+       if (!cached && !(buffer->private_flags & ION_PRIV_FLAG_SHRINKER_FREE)) {
                struct ion_page_pool *pool = heap->pools[order_to_index(order)];
                ion_page_pool_free(pool, page);
        } else {
@@ -205,7 +205,7 @@ static void ion_system_heap_free(struct ion_buffer *buffer)
 
        /* uncached pages come from the page pools, zero them before returning
           for security purposes (other allocations are zerod at alloc time */
-       if (!cached)
+       if (!cached && !(buffer->private_flags & ION_PRIV_FLAG_SHRINKER_FREE))
                ion_heap_buffer_zero(buffer);
 
        for_each_sg(table->sgl, sg, table->nents, i)