linux-kernel - Re: [PATCH v4 3/5] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap

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Date:   Fri, 21 Sep 2018 20:14:32 +0000
From:   Pasha Tatashin <Pavel.Tatashin@...rosoft.com>
To:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
CC:     "mhocko@...e.com" <mhocko@...e.com>,
        "dave.jiang@...el.com" <dave.jiang@...el.com>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>,
        "jglisse@...hat.com" <jglisse@...hat.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "logang@...tatee.com" <logang@...tatee.com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v4 3/5] mm: Defer ZONE_DEVICE page initialization to the
 point where we init pgmap


>>> +        page->pgmap = pgmap;
>>> +        page->hmm_data = 0;
>>
>> __init_single_page()
>>    mm_zero_struct_page()
>>
>> Takes care of zeroing, no need to do another store here.
> 
> The problem is __init_singe_page also calls INIT_LIST_HEAD which I
> believe sets the prev pointer which overlaps with hmm_data.

Indeed it does:

INIT_LIST_HEAD(&page->lru); overlaps with hmm_data, and before
list_del(&page->lru); was called to remove from the list.

And now I see you also mentioned about this in comments. I also prefer
having it zeroed instead of left poisoned or uninitialized. The change
looks good.

Thank you,
Pavel

> 
>>
>> Looks good otherwise.
>>
>> Reviewed-by: Pavel Tatashin <pavel.tatashin@...rosoft.com>
>>
> 
> Thanks for the review.
>