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From:   Pavel Tatashin <pasha.tatashin@oracle.com>
Date:   Tue, 13 Mar 2018 20:59:04 -0400
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Subject: Re: [v5 1/2] mm: disable interrupts while initializing deferred pages
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Steven Sistare <steven.sistare@oracle.com>,
        Daniel Jordan <daniel.m.jordan@oracle.com>,
        Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>,
        Michal Hocko <mhocko@suse.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        AKASHI Takahiro <takahiro.akashi@linaro.org>,
        Gioh Kim <gi-oh.kim@profitbricks.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Yaowei Bai <baiyaowei@cmss.chinamobile.com>,
        Wei Yang <richard.weiyang@gmail.com>,
        Paul Burton <paul.burton@mips.com>,
        Miles Chen <miles.chen@mediatek.com>,
        Vlastimil Babka <vbabka@suse.cz>, Mel Gorman <mgorman@suse.de>,
        Johannes Weiner <hannes@cmpxchg.org>,
        LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org
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> hm, maybe.  But I'm not sure that touch_nmi_watchdog() will hold off a
> soft lockup warning.  Maybe it will.

It should:

124static inline void touch_nmi_watchdog(void)
125{
126 arch_touch_nmi_watchdog();
127 touch_softlockup_watchdog();
128}

>
> And please let's get the above thoughts into the changlog.

OK

>
>> >
>> > I'm not sure what to suggest, really.  Your changelog isn't the best:
>> > "Vlastimil Babka reported about a window issue during which when
>> > deferred pages are initialized, and the current version of on-demand
>> > initialization is finished, allocations may fail".  Well...  where is
>> > ths mysterious window?  Without such detail it's hard for others to
>> > suggest alternative approaches.
>>
>> Here is hopefully a better description of the problem:
>>
>> Currently, during boot we preinitialize some number of struct pages to s=
atisfy all boot allocations. Even if these allocations happen when we initi=
alize the reset of deferred pages in page_alloc_init_late(). The problem is=
 that we do not know how much kernel will need, and it also depends on vari=
ous options.
>>
>> So, with this work, we are changing this behavior to initialize struct p=
ages on-demand, only when allocations happen.
>>
>> During boot, when we try to allocate memory, the on-demand struct page i=
nitialization code takes care of it. But, once the deferred pages are initi=
alizing in:
>>
>> page_alloc_init_late()
>>    for_each_node_state(nid, N_MEMORY)
>>       kthread_run(deferred_init_memmap())
>>
>> We cannot use on-demand initialization, as these threads resize pgdat.
>>
>> This whole thing is to take care of this time.
>>
>> My first version of on-demand deferred page initialization would simply =
fail to allocate memory during this period of time. But, this new version w=
aits for threads to finish initializing deferred memory, and successfully p=
erform the allocation.
>>
>> Because interrupt handler would wait for pgdat resize lock.
>
> OK, thanks.  Please also add to changelog.

OK, I will send an updated patch, with changelog changes.