From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
Let us look at the timeline of scenarios below with WMARK_LOW=25MB WMARK_MIN=5MB
(managed pages 1.9GB). We can find that CMA begin to be used until 'C' under the
method of 'fixed 2 times of free cma over free pages' which could have the
scenario 'A' and 'B' into a fault state, that is, free UNMOVABLE & RECLAIMABLE
pages is lower than corresponding watermark without reclaiming which should be
deemed as against current memory policy. This commit try to solve this by
checking zone_watermark_ok again with removing CMA pages which could lead to a
proper time point of CMA's utilization.
-- Free_pages
|
|
-- WMARK_LOW
|
-- Free_CMA
|
|
--
Free_CMA/Free_pages(MB) A(12/30) --> B(12/25) --> C(12/20)
fixed 1/2 ratio N N Y
this commit Y Y Y
Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
---
v2: do proportion check when zone_watermark_ok, update commit message
v3: update coding style and simplify the logic when zone_watermark_ok
v4: code update according to Roman's suggest
v5: update commit message
---
---
mm/page_alloc.c | 44 ++++++++++++++++++++++++++++++++++++++++----
1 file changed, 40 insertions(+), 4 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0745aed..4719800 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3071,6 +3071,43 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
}
+#ifdef CONFIG_CMA
+/*
+ * GFP_MOVABLE allocation could drain UNMOVABLE & RECLAIMABLE page blocks via
+ * the help of CMA which makes GFP_KERNEL failed. Checking if zone_watermark_ok
+ * again without ALLOC_CMA to see if to use CMA first.
+ */
+static bool use_cma_first(struct zone *zone, unsigned int order, unsigned int alloc_flags)
+{
+ unsigned long watermark;
+ bool cma_first = false;
+
+ watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
+ /* check if GFP_MOVABLE pass previous zone_watermark_ok via the help of CMA */
+ if (zone_watermark_ok(zone, order, watermark, 0, alloc_flags & (~ALLOC_CMA))) {
+ /*
+ * Balance movable allocations between regular and CMA areas by
+ * allocating from CMA when over half of the zone's free memory
+ * is in the CMA area.
+ */
+ cma_first = (zone_page_state(zone, NR_FREE_CMA_PAGES) >
+ zone_page_state(zone, NR_FREE_PAGES) / 2);
+ } else {
+ /*
+ * watermark failed means UNMOVABLE & RECLAIMBLE is not enough
+ * now, we should use cma first to keep them stay around the
+ * corresponding watermark
+ */
+ cma_first = true;
+ }
+ return cma_first;
+}
+#else
+static bool use_cma_first(struct zone *zone, unsigned int order, unsigned int alloc_flags)
+{
+ return false;
+}
+#endif
/*
* Do the hard work of removing an element from the buddy allocator.
* Call me with the zone->lock already held.
@@ -3084,12 +3121,11 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
if (IS_ENABLED(CONFIG_CMA)) {
/*
* Balance movable allocations between regular and CMA areas by
- * allocating from CMA when over half of the zone's free memory
- * is in the CMA area.
+ * allocating from CMA base on judging zone_watermark_ok again
+ * to see if the latest check got pass via the help of CMA
*/
if (alloc_flags & ALLOC_CMA &&
- zone_page_state(zone, NR_FREE_CMA_PAGES) >
- zone_page_state(zone, NR_FREE_PAGES) / 2) {
+ use_cma_first(zone, order, alloc_flags)) {
page = __rmqueue_cma_fallback(zone, order);
if (page)
return page;
--
1.9.1
