linux-kernel - Re: [PATCH V8 2/2] arm64/mm: Enable memory hot remove

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Message-ID: <962f7849-f42d-9154-92ae-3125d2f19504@arm.com>
Date:   Tue, 24 Sep 2019 14:11:12 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, akpm@...ux-foundation.org,
        catalin.marinas@....com, will@...nel.org, mark.rutland@....com,
        mhocko@...e.com, david@...hat.com, cai@....pw, logang@...tatee.com,
        cpandya@...eaurora.org, arunks@...eaurora.org,
        dan.j.williams@...el.com, mgorman@...hsingularity.net,
        osalvador@...e.de, ard.biesheuvel@....com, steve.capper@....com,
        broonie@...nel.org, valentin.schneider@....com,
        Robin.Murphy@....com, steven.price@....com, suzuki.poulose@....com,
        ira.weiny@...el.com
Subject: Re: [PATCH V8 2/2] arm64/mm: Enable memory hot remove



On 09/23/2019 04:47 PM, Matthew Wilcox wrote:
> On Mon, Sep 23, 2019 at 11:13:45AM +0530, Anshuman Khandual wrote:
>> +#ifdef CONFIG_MEMORY_HOTPLUG
>> +static void free_hotplug_page_range(struct page *page, size_t size)
>> +{
>> +	WARN_ON(!page || PageReserved(page));
> 
> WARN_ON(!page) isn't terribly useful.  You're going to crash on the very
> next line when you call page_address() anyway.  If this line were
> 
> 	if (WARN_ON(!page || PageReserved(page)))
> 		return;
> 
> it would make sense, or if it were just
> 
> 	WARN_ON(PageReserved(page))
> 
> it would also make sense.

I guess WARN_ON(PageReserved(page)) should be good enough to make sure
that page being freed here was originally allocated at runtime for a
previous memory hot add operation and did not some how come from the
memblock reserved area. That was the original objective for this check.
Will change it.

> 
>> +	free_pages((unsigned long)page_address(page), get_order(size));
>> +}
>