linux-kernel - Re: [PATCH v2 1/1] mm, memory_hotplug: Initialize struct pages for the full memory section

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Message-ID: <20181215002613.gj3s62uuxad6n4rb@master>
Date:   Sat, 15 Dec 2018 00:26:13 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Zaslonko Mikhail <zaslonko@...ux.ibm.com>,
        Wei Yang <richard.weiyang@...il.com>,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Pavel.Tatashin@...rosoft.com,
        schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
        gerald.schaefer@...ibm.com
Subject: Re: [PATCH v2 1/1] mm, memory_hotplug: Initialize struct pages for
 the full memory section

On Fri, Dec 14, 2018 at 11:19:59AM +0100, Michal Hocko wrote:
>[Your From address seems to have a typo (linux.bm.com) - fixed]
>
>On Fri 14-12-18 10:33:55, Zaslonko Mikhail wrote:
>[...]
>> Yes, it might still trigger PF_POISONED_CHECK if the first page 
>> of the pageblock is left uninitialized (poisoned).
>> But in order to cover these exceptional cases we would need to 
>> adjust memory_hotplug sysfs handler functions with similar 
>> checks (as in the for loop of memmap_init_zone()). And I guess 
>> that is what we were trying to avoid (adding special cases to 
>> memory_hotplug paths).
>
>is_mem_section_removable should test pfn_valid_within at least.
>But that would require some care because next_active_pageblock expects
>aligned pages. Ble, this code is just horrible. I would just remove it
>altogether. I strongly suspect that nobody is using it for anything
>reasonable anyway. The only reliable way to check whether a block is
>removable is to remove it. Everything else is just racy.
>

Sounds reasonable.

The result return from removable sysfs is transient. If no user rely on
this, remove this is a better way.

>-- 
>Michal Hocko
>SUSE Labs

-- 
Wei Yang
Help you, Help me