linux-kernel - Re: [RFCv2 3/6] mm: introduce MADV

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Message-ID: <20190531231438.GA248371@google.com>
Date:   Sat, 1 Jun 2019 08:14:38 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-api@...r.kernel.org,
        Michal Hocko <mhocko@...e.com>,
        Tim Murray <timmurray@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Daniel Colascione <dancol@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Brian Geffon <bgeffon@...gle.com>, jannh@...gle.com,
        oleg@...hat.com, christian@...uner.io, oleksandr@...hat.com,
        hdanton@...a.com
Subject: Re: [RFCv2 3/6] mm: introduce MADV_PAGEOUT

Hey Johannes,

On Fri, May 31, 2019 at 12:59:27PM -0400, Johannes Weiner wrote:
> Hi Michan,
> 
> this looks pretty straight-forward to me, only one kink:
> 
> On Fri, May 31, 2019 at 03:43:10PM +0900, Minchan Kim wrote:
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -2126,6 +2126,83 @@ static void shrink_active_list(unsigned long nr_to_scan,
> >  			nr_deactivate, nr_rotated, sc->priority, file);
> >  }
> >  
> > +unsigned long reclaim_pages(struct list_head *page_list)
> > +{
> > +	int nid = -1;
> > +	unsigned long nr_isolated[2] = {0, };
> > +	unsigned long nr_reclaimed = 0;
> > +	LIST_HEAD(node_page_list);
> > +	struct reclaim_stat dummy_stat;
> > +	struct scan_control sc = {
> > +		.gfp_mask = GFP_KERNEL,
> > +		.priority = DEF_PRIORITY,
> > +		.may_writepage = 1,
> > +		.may_unmap = 1,
> > +		.may_swap = 1,
> > +	};
> > +
> > +	while (!list_empty(page_list)) {
> > +		struct page *page;
> > +
> > +		page = lru_to_page(page_list);
> > +		if (nid == -1) {
> > +			nid = page_to_nid(page);
> > +			INIT_LIST_HEAD(&node_page_list);
> > +			nr_isolated[0] = nr_isolated[1] = 0;
> > +		}
> > +
> > +		if (nid == page_to_nid(page)) {
> > +			list_move(&page->lru, &node_page_list);
> > +			nr_isolated[!!page_is_file_cache(page)] +=
> > +						hpage_nr_pages(page);
> > +			continue;
> > +		}
> > +
> > +		mod_node_page_state(NODE_DATA(nid), NR_ISOLATED_ANON,
> > +					nr_isolated[0]);
> > +		mod_node_page_state(NODE_DATA(nid), NR_ISOLATED_FILE,
> > +					nr_isolated[1]);
> > +		nr_reclaimed += shrink_page_list(&node_page_list,
> > +				NODE_DATA(nid), &sc, TTU_IGNORE_ACCESS,
> > +				&dummy_stat, true);
> > +		while (!list_empty(&node_page_list)) {
> > +			struct page *page = lru_to_page(&node_page_list);
> > +
> > +			list_del(&page->lru);
> > +			putback_lru_page(page);
> > +		}
> > +		mod_node_page_state(NODE_DATA(nid), NR_ISOLATED_ANON,
> > +					-nr_isolated[0]);
> > +		mod_node_page_state(NODE_DATA(nid), NR_ISOLATED_FILE,
> > +					-nr_isolated[1]);
> > +		nid = -1;
> > +	}
> > +
> > +	if (!list_empty(&node_page_list)) {
> > +		mod_node_page_state(NODE_DATA(nid), NR_ISOLATED_ANON,
> > +					nr_isolated[0]);
> > +		mod_node_page_state(NODE_DATA(nid), NR_ISOLATED_FILE,
> > +					nr_isolated[1]);
> > +		nr_reclaimed += shrink_page_list(&node_page_list,
> > +				NODE_DATA(nid), &sc, TTU_IGNORE_ACCESS,
> > +				&dummy_stat, true);
> > +		mod_node_page_state(NODE_DATA(nid), NR_ISOLATED_ANON,
> > +					-nr_isolated[0]);
> > +		mod_node_page_state(NODE_DATA(nid), NR_ISOLATED_FILE,
> > +					-nr_isolated[1]);
> > +
> > +		while (!list_empty(&node_page_list)) {
> > +			struct page *page = lru_to_page(&node_page_list);
> > +
> > +			list_del(&page->lru);
> > +			putback_lru_page(page);
> > +		}
> > +
> > +	}
> 
> The NR_ISOLATED accounting, nid parsing etc. is really awkward and
> makes it hard to see what the function actually does.
> 
> Can you please make those ISOLATED counters part of the isolation API?
> Your patch really shows this is an overdue cleanup.

Yeah, that was very painful.

> 
> These are fast local percpu counters, we don't need the sprawling
> batching we do all over vmscan.c, migrate.c, khugepaged.c,
> compaction.c etc. Isolation can increase the counter page by page, and
> reclaim or putback can likewise decrease them one by one.
> 
> It looks like mlock is the only user of the isolation api that does
> not participate in the NR_ISOLATED_* counters protocol, but I don't
> see why it wouldn't, or why doing so would hurt.
> 
> There are also seem to be quite a few callsites that use the atomic
> versions of the counter API when they're clearly under the irqsafe
> lru_lock. That would be fixed automatically by this work as well.

I agree all points so will prepare clean up patch.