linux-kernel - Re: [PATCH v3] mm/page_owner: fix for deferred struct page init

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Date:   Thu, 20 Dec 2018 16:04:46 -0500
From:   Qian Cai <cai@....pw>
To:     William Kucharski <william.kucharski@...cle.com>
Cc:     akpm@...ux-foundation.org, mhocko@...e.com,
        Pavel.Tatashin@...rosoft.com, mingo@...nel.org, hpa@...or.com,
        mgorman@...hsingularity.net, iamjoonsoo.kim@....com,
        tglx@...utronix.de, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mm/page_owner: fix for deferred struct page init

On Thu, 2018-12-20 at 14:00 -0700, William Kucharski wrote:
> > On Dec 20, 2018, at 1:31 PM, Qian Cai <cai@....pw> wrote:
> > 
> > diff --git a/mm/page_ext.c b/mm/page_ext.c
> > index ae44f7adbe07..d76fd51e312a 100644
> > --- a/mm/page_ext.c
> > +++ b/mm/page_ext.c
> > @@ -399,9 +399,8 @@ void __init page_ext_init(void)
> > 			 * -------------pfn-------------->
> > 			 * N0 | N1 | N2 | N0 | N1 | N2|....
> > 			 *
> > -			 * Take into account DEFERRED_STRUCT_PAGE_INIT.
> > 			 */
> > -			if (early_pfn_to_nid(pfn) != nid)
> > +			if (pfn_to_nid(pfn) != nid)
> > 				continue;
> > 			if (init_section_page_ext(pfn, nid))
> > 				goto oom;
> > -- 
> > 2.17.2 (Apple Git-113)
> > 
> 
> Is there any danger in the fact that in the CONFIG_NUMA case in mmzone.h
> (around line 1261), pfn_to_nid() calls page_to_nid(), possibly causing the
> same issue seen in v2?
> 

No. If CONFIG_DEFERRED_STRUCT_PAGE_INIT=y, page_ext_init() is called after
page_alloc_init_late() where all the memory has already been initialized,
so page_to_nid() will work then.