linux-kernel - Re: [PATCH v4 3/9] mm/lru: replace pgdat lru

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Date:   Tue, 19 Nov 2019 07:57:04 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org,
        mgorman@...hsingularity.net, tj@...nel.org, hughd@...gle.com,
        khlebnikov@...dex-team.ru, daniel.m.jordan@...cle.com,
        yang.shi@...ux.alibaba.com, shakeelb@...gle.com,
        hannes@...xchg.org, Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Roman Gushchin <guro@...com>,
        Chris Down <chris@...isdown.name>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vlastimil Babka <vbabka@...e.cz>, Qian Cai <cai@....pw>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        swkhack <swkhack@...il.com>,
        "Potyra, Stefan" <Stefan.Potyra@...ktrobit.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Colin Ian King <colin.king@...onical.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Peng Fan <peng.fan@....com>,
        Nikolay Borisov <nborisov@...e.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Yafang Shao <laoar.shao@...il.com>
Subject: Re: [PATCH v4 3/9] mm/lru: replace pgdat lru_lock with lruvec lock

On Tue, Nov 19, 2019 at 08:23:17PM +0800, Alex Shi wrote:
> +static inline struct lruvec *lock_page_lruvec_irqsave(struct page *page,
> +				struct pglist_data *pgdat, unsigned long *flags)
> +{
> +	struct lruvec *lruvec = mem_cgroup_page_lruvec(page, pgdat);
> +
> +	spin_lock_irqsave(&lruvec->lru_lock, *flags);
> +
> +	return lruvec;
> +}

This should be a macro, not a function.  You basically can't do this;
spin_lock_irqsave needs to write to a variable which can then be passed
to spin_unlock_irqrestore().  What you're doing here will dereference the
pointer in _this_ function, but won't propagate the modified value back to
the caller.  I suppose you could do something like this ...

static inline struct lruvec *lock_page_lruvec_irqsave(struct page *page,
			struct pglist_data *pgdat, unsigned long *flagsp)
{
	unsigned long flags;
	struct lruvec *lruvec = mem_cgroup_page_lruvec(page, pgdat);

	spin_lock_irqsave(&lruvec->lru_lock, flags);
	*flagsp = flags;

	return lruvec;
}

Almost certainly easier to write a macro though.

You shouldn't need the two prior patches with this kind of change.