mm, vmstat: drop zone->lock in /proc/pagetypeinfo

Commit 93b3a674485f6a4b8ffff85d1682d5e8b7c51560 upstream

Commit 93b3a674485f ("mm,vmstat: reduce zone->lock holding time by
/proc/pagetypeinfo") upstream caps the number of iterations over each
free_list at 100,000, and also drops the zone->lock in between each
migrate type. Capping the iteration count alters the file contents in
some cases, which means this approach may not be suitable for stable
backports.

However, dropping zone->lock in between migrate types (and, as a result,
page orders) will not change the /proc/pagetypeinfo file contents. It
can significantly reduce the length of time spent with IRQs disabled,
which can prevent missed interrupts or soft lockups which we have
observed on systems with particularly large memory.

Thus, this commit is a modified version of the upstream one which only
drops the lock in between migrate types.

Fixes: 467c996c1e19 ("Print out statistics in relation to fragmentation avoidance to /proc/pagetypeinfo")
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
Reviewed-by: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
Reviewed-by: Khalid Aziz <khalid.aziz@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/vmstat.c b/mm/vmstat.c
index ce81b0a7d0186d38c68ace255c79fd744d2d153b..21e07e71ea2dfad8c7866225868c29af74131cbd 100644 (file)
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1384,6 +1384,9 @@ static void pagetypeinfo_showfree_print(struct seq_file *m,
                        list_for_each(curr, &area->free_list[mtype])
                                freecount++;
                        seq_printf(m, "%6lu ", freecount);
+                       spin_unlock_irq(&zone->lock);
+                       cond_resched();
+                       spin_lock_irq(&zone->lock);
                }
                seq_putc(m, '\n');
        }