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Date:   Tue, 12 Nov 2019 06:36:24 -0800
From:   Matthew Wilcox <willy@infradead.org>
To:     Alex Shi <alex.shi@linux.alibaba.com>
Cc:     cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, akpm@linux-foundation.org,
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        Jason Gunthorpe <jgg@ziepe.ca>,
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        Ira Weiny <ira.weiny@intel.com>,
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        Yafang Shao <laoar.shao@gmail.com>
Subject: Re: [PATCH v2 4/8] mm/lru: only change the lru_lock iff page's
 lruvec is different
Message-ID: <20191112143624.GA7934@bombadil.infradead.org>
References: <1573567588-47048-1-git-send-email-alex.shi@linux.alibaba.com>
 <1573567588-47048-5-git-send-email-alex.shi@linux.alibaba.com>
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On Tue, Nov 12, 2019 at 10:06:24PM +0800, Alex Shi wrote:
> +/* Don't lock again iff page's lruvec locked */
> +static inline struct lruvec *relock_page_lruvec_irq(struct page *page,
> +					struct lruvec *locked_lruvec)
> +{
> +	struct pglist_data *pgdat = page_pgdat(page);
> +	struct lruvec *lruvec;
> +
> +	rcu_read_lock();
> +	lruvec = mem_cgroup_page_lruvec(page, pgdat);
> +
> +	if (locked_lruvec == lruvec) {
> +		rcu_read_unlock();
> +		return lruvec;
> +	}
> +	rcu_read_unlock();

Why not simply:

	rcu_read_lock();
	lruvec = mem_cgroup_page_lruvec(page, pgdat);
	rcu_read_unlock();

	if (locked_lruvec == lruvec)
		return lruvec;

Also, why are you bothering to re-enable interrupts here?  Surely if
you're holding lock A with interrupts disabled , you can just drop lock A,
acquire lock B and leave the interrupts alone.  That way you only need
one of this variety of function, and not the separate irq/irqsave variants.