linux-kernel - Re: [PATCH v8 03/10] mm/lru: replace pgdat lru

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Date:   Thu, 16 Apr 2020 16:01:20 +0800
From:   Alex Shi <alex.shi@...ux.alibaba.com>
To:     Johannes Weiner <hannes@...xchg.org>, akpm@...ux-foundation.org
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, mgorman@...hsingularity.net, tj@...nel.org,
        hughd@...gle.com, khlebnikov@...dex-team.ru,
        daniel.m.jordan@...cle.com, yang.shi@...ux.alibaba.com,
        willy@...radead.org, shakeelb@...gle.com,
        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>,
        Wei Yang <richard.weiyang@...il.com>
Subject: Re: [PATCH v8 03/10] mm/lru: replace pgdat lru_lock with lruvec lock



在 2020/4/15 下午9:42, Alex Shi 写道:
> Hi Johannes,
> 
> Thanks a lot for point out!
> 
> Charging in __read_swap_cache_async would ask for 3 layers function arguments
> pass, that would be a bit ugly. Compare to this, could we move out the
> lru_cache add after commit_charge, like ksm copied pages?
> 
> That give a bit extra non lru list time, but the page just only be used only
> after add_anon_rmap setting. Could it cause troubles?

Hi Johannes & Andrew,

Doing lru_cache_add_anon during swapin_readahead can give a very short timing 
for possible page reclaiming for these few pages.

If we delay these few pages lru adding till after the vm_fault target page 
get memcg charging(mem_cgroup_commit_charge) and activate, we could skip the 
mem_cgroup_try_charge/commit_charge/cancel_charge process in __read_swap_cache_async().
But the cost is maximum SWAP_RA_ORDER_CEILING number pages on each cpu miss
page reclaiming in a short time. On the other hand, save the target vm_fault
page from reclaiming before activate it during that time.

Judging the lose and gain, and the example of shmem/ksm copied pages, I believe 
it's fine to delay lru list adding till activate the target swapin page.

Any comments are appreciated! 

Thanks
Alex


> 
> I tried to track down the reason of lru_cache_add here, but no explanation
> till first git kernel commit.
> 
> Thanks
> Alex 
>