[PATCH 5/5] mm: add debugfs interface for parallel free tuning

Aaron Lu
2017-02-24T11:41:23Z

Make it possible to set different values for async_free_threshold and
max_gather_batch_count through debugfs.

With this, we can do tests for different purposes:
1 Restore vanilla kernel bahaviour for performance comparison.
Set max_gather_batch_count to a value like 20 to effectively restore
the behaviour of vanilla kernel since this will make page gathered
always smaller than async_free_threshold(effectively disable parallel
free);
2 Debug purpose.
Set async_free_threshold to a very small value(like 128) to trigger
parallel free even on ordinary processes, ideal for debug purpose with
a virtual machine that doesn't have much memory assigned to it;
3 Performance tuning.
Use a different value for async_free_threshold and max_gather_batch_count
other than the default to test if parallel free performs better or worse.

Signed-off-by: Aaron Lu <aaron.lu@intel.com>
---
mm/memory.c | 33 +++++++++++++++++++++++++++++++--
1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 7d1fe74084be..9ca07c59e525 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -184,6 +184,35 @@ static void check_sync_rss_stat(struct task_struct *task)

#ifdef HAVE_GENERIC_MMU_GATHER

+static unsigned long async_free_threshold = ASYNC_FREE_THRESHOLD;
+static unsigned long max_gather_batch_count = MAX_GATHER_BATCH_COUNT;
+
+#ifdef CONFIG_DEBUG_FS
+static int __init tlb_mmu_parallel_free_debugfs(void)
+{
+ umode_t mode = S_IFREG | S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
+ struct dentry *dir;
+
+ dir = debugfs_create_dir("parallel_free", NULL);
+ if (!dir)
+ return -ENOMEM;
+
+ if (!debugfs_create_ulong("async_free_threshold", mode, dir,
+ &async_free_threshold))
+ goto fail;
+ if (!debugfs_create_ulong("max_gather_batch_count", mode, dir,
+ &max_gather_batch_count))
+ goto fail;
+
+ return 0;
+
+fail:
+ debugfs_remove_recursive(dir);
+ return -ENOMEM;
+}
+late_initcall(tlb_mmu_parallel_free_debugfs);
+#endif
+
static bool tlb_next_batch(struct mmu_gather *tlb)
{
struct mmu_gather_batch *batch;
@@ -194,7 +223,7 @@ static bool tlb_next_batch(struct mmu_gather *tlb)
return true;
}

- if (tlb->batch_count == MAX_GATHER_BATCH_COUNT)
+ if (tlb->batch_count == max_gather_batch_count)
return false;

batch = (void *)__get_free_pages(GFP_NOWAIT | __GFP_NOWARN, 0);
@@ -306,7 +335,7 @@ static void tlb_flush_mmu_free(struct mmu_gather *tlb)
{
struct batch_free_struct *batch_free = NULL;

- if (tlb->page_nr >= ASYNC_FREE_THRESHOLD)
+ if (tlb->page_nr >= async_free_threshold)
batch_free = kmalloc(sizeof(*batch_free), GFP_NOWAIT | __GFP_NOWARN);

if (batch_free) {
--
2.9.3