cma_release() has to lock the cma_lock mutex to clear the cma bitmap.
It makes it a blocking function, which complicates its usage from
non-blocking contexts. For instance, hugetlbfs code is temporarily
dropping the hugetlb_lock spinlock to call cma_release().
This patch makes cma_release non-blocking by postponing the cma
bitmap clearance. It's done later from a work context. The first page
in the cma allocation is used to store the work struct.
To make sure that subsequent cma_alloc() call will pass, cma_alloc()
flushes the corresponding workqueue.
Because CMA allocations and de-allocations are usually not that
frequent, a single global workqueue is used.
Signed-off-by: Roman Gushchin <g...@fb.com>
---
mm/cma.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 49 insertions(+), 2 deletions(-)
diff --git a/mm/cma.c b/mm/cma.c
index 7f415d7cda9f..523cd9356bc7 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -36,10 +36,19 @@
#include "cma.h"
+struct cma_clear_bitmap_work {
+ struct work_struct work;
+ struct cma *cma;
+ unsigned long pfn;
+ unsigned int count;
+};
+
struct cma cma_areas[MAX_CMA_AREAS];
unsigned cma_area_count;
static DEFINE_MUTEX(cma_mutex);
+struct workqueue_struct *cma_release_wq;
+
phys_addr_t cma_get_base(const struct cma *cma)
{
return PFN_PHYS(cma->base_pfn);
@@ -148,6 +157,10 @@ static int __init cma_init_reserved_areas(void)
for (i = 0; i < cma_area_count; i++)
cma_activate_area(&cma_areas[i]);
+ cma_release_wq = create_workqueue("cma_release");
+ if (!cma_release_wq)
+ return -ENOMEM;
+
return 0;
}
core_initcall(cma_init_reserved_areas);
@@ -437,6 +450,13 @@ struct page *cma_alloc(struct cma *cma, size_t count,
unsigned int align,
return NULL;
for (;;) {
+ /*
+ * CMA bitmaps are cleared asynchronously from works,
+ * scheduled by cma_release(). To make sure the allocation
+ * will success, cma release workqueue is flushed here.
+ */
+ flush_workqueue(cma_release_wq);
+
mutex_lock(&cma->lock);
bitmap_no = bitmap_find_next_zero_area_off(cma->bitmap,
bitmap_maxno, start, bitmap_count, mask,
@@ -495,6 +515,17 @@ struct page *cma_alloc(struct cma *cma, size_t count,
unsigned int align,
return page;
}
+static void cma_clear_bitmap_fn(struct work_struct *work)
+{
+ struct cma_clear_bitmap_work *w;
+
+ w = container_of(work, struct cma_clear_bitmap_work, work);
+
+ cma_clear_bitmap(w->cma, w->pfn, w->count);
+
+ __free_page(pfn_to_page(w->pfn));
+}
+
/**
* cma_release() - release allocated pages
* @cma: Contiguous memory region for which the allocation is performed.
@@ -507,6 +538,7 @@ struct page *cma_alloc(struct cma *cma, size_t count,
unsigned int align,
*/
bool cma_release(struct cma *cma, const struct page *pages, unsigned int count)
{
+ struct cma_clear_bitmap_work *work;
unsigned long pfn;
if (!cma || !pages)
@@ -521,8 +553,23 @@ bool cma_release(struct cma *cma, const struct page
*pages, unsigned int count)
VM_BUG_ON(pfn + count > cma->base_pfn + cma->count);
- free_contig_range(pfn, count);
- cma_clear_bitmap(cma, pfn, count);
+ /*
+ * To make cma_release() non-blocking, cma bitmap is cleared from
+ * a work context (see cma_clear_bitmap_fn()). The first page
+ * in the cma allocation is used to store the work structure,
+ * so it's released after the cma bitmap clearance. Other pages
+ * are released immediately as previously.
+ */
+ if (count > 1)
+ free_contig_range(pfn + 1, count - 1);
+
+ work = (struct cma_clear_bitmap_work *)page_to_virt(pages);
+ INIT_WORK(&work->work, cma_clear_bitmap_fn);
+ work->cma = cma;
+ work->pfn = pfn;
+ work->count = count;
+ queue_work(cma_release_wq, &work->work);
+
trace_cma_release(pfn, pages, count);
return true;
--
2.26.2
