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Date:   Fri, 14 Dec 2018 11:19:59 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     Zaslonko Mikhail <zaslonko@linux.ibm.com>
Cc:     Wei Yang <richard.weiyang@gmail.com>,
        Mikhail Zaslonko <zaslonko@linux.ibm.com>,
        akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Pavel.Tatashin@microsoft.com,
        schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com,
        gerald.schaefer@de.ibm.com
Subject: Re: [PATCH v2 1/1] mm, memory_hotplug: Initialize struct pages for
 the full memory section
Message-ID: <20181214101651.GE5624@dhcp22.suse.cz>
References: <20181212172712.34019-1-zaslonko@linux.ibm.com>
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 <20181213034615.4ntpo4cl2oo5mcx4@master>
 <e4cebbae-3fcb-f03c-3d0e-a1a44ff0675a@linux.bm.com>
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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.

-- 
Michal Hocko
SUSE Labs