linux-kernel - Re: [RFC PATCH] page_ext: create page extension for all memblock memory regions

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Message-ID: <YoT1LMALyqTUtg6e@linux.ibm.com>
Date:   Wed, 18 May 2022 16:31:24 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Jaewon Kim <jaewon31.kim@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Jaewon Kim <jaewon31.kim@...sung.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [RFC PATCH] page_ext: create page extension for all memblock
 memory regions

On Tue, May 17, 2022 at 10:10:20PM +0900, Jaewon Kim wrote:
> 64
> 59
> 
> 2022년 5월 17일 (화) 오후 9:55, Mike Rapoport <rppt@...ux.ibm.com>님이 작성:
> >
> > On Tue, May 17, 2022 at 08:38:18PM +0900, Jaewon Kim wrote:
> > > Hello Mike Rapoport
> > > Thank you for your comment.
> > >
> > > Oh really? Could you point out the code or the commit regarding 'all
> > > struct pages in any section should be valid and
> > > properly initialized' ?
> >
> > There were several commits that refactored the memory map initialization,
> > freeing of the unused memory map and abuse of pfn_valid() as a substitute
> > of "is memory valid" semantics.
> >
> > > Actually I am using v5.10 based source tree on an arm64 device.
> >
> > Then most probably your change is not relevant for the upstream kernel.
> > Did you observe any issues with page_ext initialization on v5.18-rcN
> > kernels?
> 
> Actually I observed only 59 sections were initialized for page_ext and
> missed 5 sections.
> It should be totally 64 sections * 128 MB = 8,192 MB

Does this happen with v5.10 based kernel or with v5.18-rcN based kernel? 

> > > I tried to look up and found the following commit in v5.16-rc1, did
> > > you mean this?
> > > 3de360c3fdb3 arm64/mm: drop HAVE_ARCH_PFN_VALID
> >
> > Yes, this is one of those commits.
> >
> > > I guess memblock_is_memory code in pfn_valid in arch/arm64/mm/init.c, v5.10
> > > might affect the page_ext_init.
> >
> > Yes. In 5.10 the pfn_valid() test in page_ext_init() will skip an entire
> > section if the first pfn in that section is not memory that can be mapped
> > in the linear map.
> >
> > But again, this should be fixed in the latest kernels.
> 
> Great! Thank you for your explanation.
> I will check it someday later when I use the latest kernel on our devices.
> The next version on our devices seems to be v5.15 though.
> 
> Thank you
> Jaewon Kim

-- 
Sincerely yours,
Mike.