mm/page_alloc.c: avoid excessive IRQ disabled times in free_unref_page_list()

Since commit 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@pengutronix.de
Fixes: 9cca35d42eb6 ("mm, page_alloc: enable/disable IRQs once when freeing a list of pages")
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 73f5d4556b3d0b7218bea0cb9bb0fdd1f1cb3cdd..7e5e775e97f400d8a050effc41f68a8261bd9a23 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2684,6 +2684,7 @@ void free_unref_page_list(struct list_head *list)
 {
        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_head *list)
                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);
 }