Re: [PATCH v4 4/5] page_idle: Drain all LRU pagevec before idle tracking
From: Michal Hocko <mhocko@kernel.org>
Date: 2019-08-06 08:44:11
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On Mon 05-08-19 13:04:50, Joel Fernandes (Google) wrote:
During idle tracking, we see that sometimes faulted anon pages are in pagevec but are not drained to LRU. Idle tracking considers pages only on LRU. Drain all CPU's LRU before starting idle tracking.
Please expand on why does this matter enough to introduce a potentially expensinve draining which has to schedule a work on each CPU and wait for them to finish.
quoted hunk ↗ jump to hunk
Signed-off-by: Joel Fernandes (Google) <redacted> --- mm/page_idle.c | 6 ++++++ 1 file changed, 6 insertions(+)diff --git a/mm/page_idle.c b/mm/page_idle.c index a5b00d63216c..2972367a599f 100644 --- a/mm/page_idle.c +++ b/mm/page_idle.c@@ -180,6 +180,8 @@ static ssize_t page_idle_bitmap_read(struct file *file, struct kobject *kobj, unsigned long pfn, end_pfn; int bit, ret; + lru_add_drain_all(); + ret = page_idle_get_frames(pos, count, NULL, &pfn, &end_pfn); if (ret == -ENXIO) return 0; /* Reads beyond max_pfn do nothing */@@ -211,6 +213,8 @@ static ssize_t page_idle_bitmap_write(struct file *file, struct kobject *kobj, unsigned long pfn, end_pfn; int bit, ret; + lru_add_drain_all(); + ret = page_idle_get_frames(pos, count, NULL, &pfn, &end_pfn); if (ret) return ret;@@ -428,6 +432,8 @@ ssize_t page_idle_proc_generic(struct file *file, char __user *ubuff, walk.private = &priv; walk.mm = mm; + lru_add_drain_all(); + down_read(&mm->mmap_sem); /*-- 2.22.0.770.g0f2c4a37fd-goog
-- Michal Hocko SUSE Labs