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Date:   Mon, 18 Nov 2019 21:10:58 -0500
From:   Daniel Jordan <daniel.m.jordan@oracle.com>
To:     Alex Shi <alex.shi@linux.alibaba.com>
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Subject: Re: [PATCH v3 3/7] mm/lru: replace pgdat lru_lock with lruvec lock
Message-ID: <20191119021058.auxc6g7vmgf7d5gg@ca-dmjordan1.us.oracle.com>
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On Sat, Nov 16, 2019 at 11:15:02AM +0800, Alex Shi wrote:
> @@ -192,26 +190,17 @@ static void pagevec_lru_move_fn(struct pagevec *pvec,
>  	void *arg)
>  {
>  	int i;
> -	struct pglist_data *pgdat = NULL;
> -	struct lruvec *lruvec;
> -	unsigned long flags = 0;
> +	struct lruvec *lruvec = NULL;
>  
>  	for (i = 0; i < pagevec_count(pvec); i++) {
>  		struct page *page = pvec->pages[i];
> -		struct pglist_data *pagepgdat = page_pgdat(page);
>  
> -		if (pagepgdat != pgdat) {
> -			if (pgdat)
> -				spin_unlock_irqrestore(&pgdat->lru_lock, flags);
> -			pgdat = pagepgdat;
> -			spin_lock_irqsave(&pgdat->lru_lock, flags);
> -		}
> +		lruvec = lock_page_lruvec_irqsave(page, page_pgdat(page));
>  
> -		lruvec = mem_cgroup_page_lruvec(page, pgdat);
>  		(*move_fn)(page, lruvec, arg);
> +		spin_unlock_irqrestore(&lruvec->lru_lock, lruvec->irqflags);
>  	}
> -	if (pgdat)
> -		spin_unlock_irqrestore(&pgdat->lru_lock, flags);
> +
>  	release_pages(pvec->pages, pvec->nr);
>  	pagevec_reinit(pvec);
>  }

Why can't you keep the locking pattern where we only drop and reacquire if the
lruvec changes?  It'd save a lot of locks and unlocks if most pages were from
the same memcg and node, or the memory controller were unused.


Thanks for running the -readtwice benchmark, by the way.