From: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
Subject: mm/page_alloc.c: avoid excessive IRQ disabled times in free_unref_page_list()
Since 9cca35d42eb6 ("mm, page_alloc: enable/disable IRQs once when
freeing a list of pages") we see excessive IRQ disabled times of up to
25ms on an embedded ARM system (tracing overhead included).
This is due to graphics buffers being freed back to the system via
release_pages(). Graphics buffers can be huge, so it's not hard to hit
cases where the list of pages to free has 2048 entries. Disabling IRQs
while freeing all those pages is clearly not a good idea.
Introduce a batch limit, which allows IRQ servicing once every few pages.
The batch count is the same as used in other parts of the MM subsystem
when dealing with IRQ disabled regions.
Link: http://lkml.kernel.org/r/20171207170314.4419-1-l.stach@xxxxxxxxxxxxxx
Fixes: 9cca35d42eb6 ("mm, page_alloc: enable/disable IRQs once when freeing a list of pages")
Signed-off-by: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff -puN mm/page_alloc.c~mm-page_alloc-avoid-excessive-irq-disabled-times-in-free_unref_page_list mm/page_alloc.c
--- a/mm/page_alloc.c~mm-page_alloc-avoid-excessive-irq-disabled-times-in-free_unref_page_list
+++ a/mm/page_alloc.c
@@ -2684,6 +2684,7 @@ void free_unref_page_list(struct list_he
{
struct page *page, *next;
unsigned long flags, pfn;
+ int batch_count = 0;
/* Prepare pages for freeing */
list_for_each_entry_safe(page, next, list, lru) {
@@ -2700,6 +2701,16 @@ void free_unref_page_list(struct list_he
set_page_private(page, 0);
trace_mm_page_free_batched(page);
free_unref_page_commit(page, pfn);
+
+ /*
+ * Guard against excessive IRQ disabled times when we get
+ * a large list of pages to free.
+ */
+ if (++batch_count == SWAP_CLUSTER_MAX) {
+ local_irq_restore(flags);
+ batch_count = 0;
+ local_irq_save(flags);
+ }
}
local_irq_restore(flags);
}
_
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
