Re: [PATCH 3/4] mm: move lazy free pages to inactive list

Minchan Kim
2015-03-30T05:35:13Z

Hello Andrew,

On Fri, Mar 20, 2015 at 03:43:58PM -0700, Andrew Morton wrote:
> On Wed, 11 Mar 2015 10:20:37 +0900 Minchan Kim <minchan@kernel.org> wrote:
>
> > MADV_FREE is hint that it's okay to discard pages if there is
> > memory pressure and we uses reclaimers(ie, kswapd and direct reclaim)
> > to free them so there is no worth to remain them in active anonymous LRU
> > so this patch moves them to inactive LRU list's head.
> >
> > This means that MADV_FREE-ed pages which were living on the inactive list
> > are reclaimed first because they are more likely to be cold rather than
> > recently active pages.
> >
> > A arguable issue for the approach would be whether we should put it to
> > head or tail in inactive list. I selected *head* because kernel cannot
> > make sure it's really cold or warm for every MADV_FREE usecase but
> > at least we know it's not *hot* so landing of inactive head would be
> > comprimise for various usecases.
> >
> > This is fixing a suboptimal behavior of MADV_FREE when pages living on
> > the active list will sit there for a long time even under memory
> > pressure while the inactive list is reclaimed heavily. This basically
> > breaks the whole purpose of using MADV_FREE to help the system to free
> > memory which is might not be used.
> >
> > @@ -789,6 +790,23 @@ static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec,
> > update_page_reclaim_stat(lruvec, file, 0);
> > }
> >
> > +
> > +static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
> > + void *arg)
> >
> > ...
> >
> > @@ -844,6 +866,18 @@ void deactivate_file_page(struct page *page)
> > }
> > }
> >
> > +void deactivate_page(struct page *page)
> > +{
>
> lru_deactivate_file_fn() and deactivate_file_page() are carefully
> documented and lru_deactivate_fn() and deactivate_page() should
> be as well. In fact it becomes more important now that we have two
> similar-looking things.

Sorry, I have missed this comment.

Acutally, deactive_file_page was too specific on file-backed page
invalidation when I implemented first time. That's why it had a lot
description but deactivate_page is too general so I think short comment
is enough. :)

Here it goes.

Thanks.

>From 1dbff1d18876962e5248346b59e41014561c09ac Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Mon, 30 Mar 2015 14:30:44 +0900
Subject: [PATCH] mm: document deactivate_page

This patch adds function description for deactivate_page.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
mm/swap.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/mm/swap.c b/mm/swap.c
index 6b5adc7..b65fc8c 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -866,6 +866,13 @@ void deactivate_file_page(struct page *page)
}
}

+/**
+ * deactivate_page - deactivate a page
+ * @page: page to deactivate
+ *
+ * This function moves @page to inactive list if @page was on active list and
+ * was not unevictable page to accelerate to reclaim @page.
+ */
void deactivate_page(struct page *page)
{
if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) {
--
1.9.3

>
>

--
Kind regards,
Minchan Kim