linux-kernel - Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap

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Date:   Fri, 28 Sep 2018 10:44:33 +0200
From:   Oscar Salvador <osalvador@...hadventures.net>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        linux-mm@...ck.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org,
        pavel.tatashin@...rosoft.com, dave.jiang@...el.com,
        dave.hansen@...el.com, jglisse@...hat.com, rppt@...ux.vnet.ibm.com,
        dan.j.williams@...el.com, logang@...tatee.com, mingo@...nel.org,
        kirill.shutemov@...ux.intel.com
Subject: Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the
 point where we init pgmap

On Fri, Sep 28, 2018 at 10:12:24AM +0200, Oscar Salvador wrote:
> Although I am not sure about leaving memmap_init_zone unprotected.
> For the normal memory, that is not a problem since the memblock's lock
> protects us from touching the same pages at the same time in online/offline_pages,
> but for HMM/devm the story is different.
> 
> I am totally unaware of HMM/devm, so I am not sure if its protected somehow.
> e.g: what happens if devm_memremap_pages and devm_memremap_pages_release are running
> at the same time for the same memory-range (with the assumption that the hotplug-lock
> does not protect move_pfn_range_to_zone anymore).

I guess that this could not happen since the device is not linked to devm_memremap_pages_release
until the end with:

devm_add_action(dev, devm_memremap_pages_release, pgmap)
-- 
Oscar Salvador
SUSE L3