Hi Eric,
On 07/04/2013 12:54 PM, Eric W. Biederman wrote:
Colin Cross <ccross@xxxxxxxxxxx> writes:
Userspace processes often have multiple allocators that each do
anonymous mmaps to get memory. When examining memory usage of
individual processes or systems as a whole, it is useful to be
able to break down the various heaps that were allocated by
each layer and examine their size, RSS, and physical memory
usage.
What is the advantage of this? It looks like it is going to add cache
line contention (atomic_inc/atomic_dec) to every vma operation
How to guarantee atomic operation cacheline? atomic_inc/atomic_dec will
lock cacheline or....?
especially in the envision use case of heavy vma_name sharing.
I would expect this will result in a bloated vm_area_struct and a slower
mm subsystem.
Have you done any benchmarks that stress the mm subsystem?
How can adding glittler to /proc/<pid>/maps and /proc/<pid>/smaps
justify putting a hand break on the linux kernel?
Eric
+/**
+ * vma_name_get
+ *
+ * Increment the refcount of an existing vma_name. No locks are needed because
+ * the caller should already be holding a reference, so refcount >= 1.
+ */
+void vma_name_get(struct vma_name *vma_name)
+{
+ if (WARN_ON(!vma_name))
+ return;
+
+ WARN_ON(!atomic_read(&vma_name->refcount));
+
+ atomic_inc(&vma_name->refcount);
+}
+
+/**
+ * vma_name_put
+ *
+ * Decrement the refcount of an existing vma_name and free it if necessary.
+ * No locks needed, takes the cache lock if it needs to remove the vma_name from
+ * the cache.
+ */
+void vma_name_put(struct vma_name *vma_name)
+{
+ int ret;
+
+ if (WARN_ON(!vma_name))
+ return;
+
+ WARN_ON(!atomic_read(&vma_name->refcount));
+
+ /* fast path: refcount > 1, decrement and return */
+ if (atomic_add_unless(&vma_name->refcount, -1, 1))
+ return;
+
+ /* slow path: take the lock, decrement, and erase node if count is 0 */
+ write_lock(&vma_name_cache_lock);
+
+ ret = atomic_dec_return(&vma_name->refcount);
+ if (ret == 0)
+ rb_erase(&vma_name->rb_node, &vma_name_cache);
+
+ write_unlock(&vma_name_cache_lock);
+
+ if (ret == 0)
+ kfree(vma_name);
+}
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