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Date:   Mon, 26 Oct 2020 16:05:05 +0800
From:   Zhenhua Huang <zhenhuah@codeaurora.org>
To:     Mike Rapoport <rppt@kernel.org>
Cc:     akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH] mm: fix page_owner initializing issue for arm32
Message-ID: <20201026080505.GA9872@codeaurora.org>
References: <1602839640-13125-1-git-send-email-zhenhuah@codeaurora.org>
 <20201025154253.GH392079@kernel.org>
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Hi Mike,

On Sun, Oct 25, 2020 at 11:42:53PM +0800, Mike Rapoport wrote:
> On Fri, Oct 16, 2020 at 05:14:00PM +0800, Zhenhua Huang wrote:
> > Page owner of pages used by page owner itself used is missing on arm32
> targets.
> > The reason is dummy_handle and failure_handle is not initialized
> correctly.
> > Buddy allocator is used to initialize these two handles. However, buddy
> > allocator is not ready when page owner calls it. This change fixed that
> by
> > initializing page owner after buddy initialization.
> > 
> > The working flow before and after this change are:
> > original logic:
> > 1. allocated memory for page_ext(using memblock).
> 
> Is anything that requires a memblock allocation FLATMEM?
> Any fundamental reason why wouldn't alloc_pages_exact_nid/vzalloc_node()
> work in this case?
> 
> It seems to me that for FLATMEM configuration we can allocate the
> page_ext using alloc_pages() with a fallback to vzalloc_node() and then
> we can unify lot's of page_ext code and entirely drop
> page_ext_init_flatmem().
> 
From comments in codes: "page_ext requires contiguous pages, bigger than
MAX_ORDER unless SPARSEMEM."
The size of page_ext for FLATMEM(which used pgdat) should be much larger
than the size for SPARSEMEM which used section.

> > 2. invoke the init callback of page_ext_ops like
> > page_owner(using buddy allocator).
> > 3. initialize buddy.
> > 
> > after this change:
> > 1. allocated memory for page_ext(using memblock).
> > 2. initialize buddy.
> > 3. invoke the init callback of page_ext_ops like
> > page_owner(using buddy allocator).
> > 
> > with the change, failure/dummy_handle can get its correct value and
> > page owner output for example has the one for page owner itself:
> > Page allocated via order 2, mask 0x6202c0(GFP_USER|__GFP_NOWARN), pid
> 1006, ts
> > 67278156558 ns
> > PFN 543776 type Unmovable Block 531 type Unmovable Flags 0x0()
> >  init_page_owner+0x28/0x2f8
> >  invoke_init_callbacks_flatmem+0x24/0x34
> >  start_kernel+0x33c/0x5d8
> >    (null)
> > 
> > Signed-off-by: Zhenhua Huang <zhenhuah@codeaurora.org>
> > ---
> >  include/linux/page_ext.h | 8 ++++++++
> >  init/main.c              | 2 ++
> >  mm/page_ext.c            | 8 +++++++-
> >  3 files changed, 17 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
> > index cfce186..aff81ba 100644
> > --- a/include/linux/page_ext.h
> > +++ b/include/linux/page_ext.h
> > @@ -44,8 +44,12 @@ static inline void page_ext_init_flatmem(void)
> >  {
> >  }
> >  extern void page_ext_init(void);
> > +static inline void page_ext_init_flatmem_late(void)
> > +{
> > +}
> >  #else
> >  extern void page_ext_init_flatmem(void);
> > +extern void page_ext_init_flatmem_late(void);
> >  static inline void page_ext_init(void)
> >  {
> >  }
> > @@ -76,6 +80,10 @@ static inline void page_ext_init(void)
> >  {
> >  }
> >  
> > +static inline void page_ext_init_flatmem_late(void)
> > +{
> > +}
> > +
> >  static inline void page_ext_init_flatmem(void)
> >  {
> >  }
> > diff --git a/init/main.c b/init/main.c
> > index 130376e..b34c475 100644
> > --- a/init/main.c
> > +++ b/init/main.c
> > @@ -818,6 +818,8 @@ static void __init mm_init(void)
> >  	init_debug_pagealloc();
> >  	report_meminit();
> >  	mem_init();
> > +	/* page_owner must be initialized after buddy is ready */
> > +	page_ext_init_flatmem_late();
> >  	kmem_cache_init();
> >  	kmemleak_init();
> >  	pgtable_init();
> > diff --git a/mm/page_ext.c b/mm/page_ext.c
> > index a3616f7..373f7a1 100644
> > --- a/mm/page_ext.c
> > +++ b/mm/page_ext.c
> > @@ -99,6 +99,13 @@ static void __init invoke_init_callbacks(void)
> >  	}
> >  }
> >  
> > +#if !defined(CONFIG_SPARSEMEM)
> > +void __init page_ext_init_flatmem_late(void)
> > +{
> > +	invoke_init_callbacks();
> > +}
> > +#endif
> > +
> >  static inline struct page_ext *get_entry(void *base, unsigned long
> index)
> >  {
> >  	return base + page_ext_size * index;
> > @@ -177,7 +184,6 @@ void __init page_ext_init_flatmem(void)
> >  			goto fail;
> >  	}
> >  	pr_info("allocated %ld bytes of page_ext\n", total_usage);
> > -	invoke_init_callbacks();
> >  	return;
> >  
> >  fail:
> > -- 
> > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
> Forum,
> > a Linux Foundation Collaborative Project
> > 
> > 
> 
> -- 
> Sincerely yours,
> Mike.
>