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 9d8936c7b40da9902345756e43f8a3c1c87d9d1b..d491a9a0fed9cec4be44ac46a8de49ac5c14e7b9 100644 (file)
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -973,6 +973,9 @@ 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');
        }