linux-kernel - Re: [PATCH v2 2/3] mm: calculate deferred pages after skipping mirrored memory

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Date:   Fri, 27 Jul 2018 10:53:24 -0400
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     osalvador@...hadventures.net
Cc:     Steven Sistare <steven.sistare@...cle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kirill.shutemov@...ux.intel.com, Michal Hocko <mhocko@...e.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        dan.j.williams@...el.com, jack@...e.cz, jglisse@...hat.com,
        Souptick Joarder <jrdr.linux@...il.com>, bhe@...hat.com,
        gregkh@...uxfoundation.org, Vlastimil Babka <vbabka@...e.cz>,
        Wei Yang <richard.weiyang@...il.com>, dave.hansen@...el.com,
        rientjes@...gle.com, mingo@...nel.org, abdhalee@...ux.vnet.ibm.com,
        mpe@...erman.id.au
Subject: Re: [PATCH v2 2/3] mm: calculate deferred pages after skipping
 mirrored memory

                         unsigned long *nr_initialised)
> > +static bool __meminit
> > +defer_init(int nid, unsigned long pfn, unsigned long end_pfn)
>
> Hi Pavel,
>
> maybe I do not understand properly the __init/__meminit macros, but should not
> "defer_init" be __init instead of __meminit?
> I think that functions marked as __meminit are not freed up, right?

Not exactly. As I understand: __meminit is the same as __init when
CONFIG_MEMORY_HOTPLUG=n. But, when memory hotplug is configured,
__meminit is not freed, because code that adds memory is shared
between boot and hotplug. In this case defer_init() is called only
during boot, and could be __init, but it is called from
memmap_init_zone() which is __meminit and thus section mismatch would
happen.

We could split memmap_init_zone() into two functions: boot and hotplug
variants, or we could use __ref, but I do not think any of that is
really needed. Keeping defer_init() in __meminit is OK, it does not
take that much memory.

>
> Reviewed-by: Oscar Salvador <osalvador@...e.de>

Thank you,
Pavel