linux-kernel - Re: [PATCH v3 3/7] mm/lru: replace pgdat lru

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Message-ID: <20191118123138.GL20752@bombadil.infradead.org>
Date:   Mon, 18 Nov 2019 04:31:38 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
Cc:     Shakeel Butt <shakeelb@...gle.com>,
        Cgroups <cgroups@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Tejun Heo <tj@...nel.org>, Hugh Dickins <hughd@...gle.com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Johannes Weiner <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 v3 3/7] mm/lru: replace pgdat lru_lock with lruvec lock

On Mon, Nov 18, 2019 at 08:23:12PM +0800, Alex Shi wrote:
> 在 2019/11/16 下午3:03, Shakeel Butt 写道:
> >> +reget_lruvec:
> >> +               lruvec = mem_cgroup_page_lruvec(page, pgdat);
> >> +
> >>                 /* If we already hold the lock, we can skip some rechecking */
> >> -               if (!locked) {
> >> -                       locked = compact_lock_irqsave(&pgdat->lru_lock,
> >> -                                                               &flags, cc);
> >> +               if (lruvec != locked_lruvec) {
> >> +                       if (locked_lruvec) {
> >> +                               spin_unlock_irqrestore(&locked_lruvec->lru_lock,
> >> +                                               locked_lruvec->irqflags);
> >> +                               locked_lruvec = NULL;
> >> +                       }
> > What guarantees the lifetime of lruvec? You should read the comment on
> > mem_cgroup_page_lruvec(). Have you seen the patches Hugh had shared?
> > Please look at the  trylock_page_lruvec().
> > 
> 
> Thanks for comments, Shakeel.
> 
> lruvec lifetime is same as memcg, which allocted in mem_cgroup_alloc()->alloc_mem_cgroup_per_node_info()
> I have read Hugh's patchset, even not every lines. But what's point of you here?

I believe Shakeel's point is that here:

struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgdat)
{
...
        memcg = page->mem_cgroup;

there is nothing pinning the memcg, and it could be freed before
dereferencing memcg->nodeinfo in mem_cgroup_page_nodeinfo().