linux-kernel - Re: [PATCH v2] mm: allow deferred page init for vmemmap only

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Message-ID: <20180510123039.GF5325@dhcp22.suse.cz>
Date:   Thu, 10 May 2018 14:30:39 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, linux-mm@...ck.org,
        mgorman@...hsingularity.net, mingo@...nel.org,
        peterz@...radead.org, rostedt@...dmis.org, fengguang.wu@...el.com,
        dennisszhou@...il.com
Subject: Re: [PATCH v2] mm: allow deferred page init for vmemmap only

On Thu 10-05-18 07:53:56, Pavel Tatashin wrote:
[...]
> Here is a sample path, where translation is required, that occurs before
> mm_init():
> 
> start_kernel()
>  trap_init()
>   setup_cpu_entry_areas()
>    setup_cpu_entry_area(cpu)
>     get_cpu_gdt_paddr(cpu)
>      per_cpu_ptr_to_phys(addr)
>       pcpu_addr_to_page(addr)
>        virt_to_page(addr)
>         pfn_to_page(__pa(addr) >> PAGE_SHIFT)

Thanks that helped me to see the problem. On the other hand isn't this a
bit of an overkill? AFAICS this affects only NEED_PER_CPU_KM which is !SMP
and DEFERRED_STRUCT_PAGE_INIT makes only very limited sense on UP,
right?

Or do we have more such places?
-- 
Michal Hocko
SUSE Labs