linux-kernel - Re: [PATCH v5 2/4] mm/sparsemem: Defer the ms->section_mem

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Date:   Thu, 28 Jun 2018 06:59:45 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Oscar Salvador <osalvador@...hadventures.net>
Cc:     linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        dave.hansen@...el.com, pagupta@...hat.com, linux-mm@...ck.org,
        kirill.shutemov@...ux.intel.com
Subject: Re: [PATCH v5 2/4] mm/sparsemem: Defer the ms->section_mem_map
 clearing

On 06/27/18 at 11:54am, Oscar Salvador wrote:
> On Wed, Jun 27, 2018 at 09:31:14AM +0800, Baoquan He wrote:
> > In sparse_init(), if CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER=y, system
> > will allocate one continuous memory chunk for mem maps on one node and
> > populate the relevant page tables to map memory section one by one. If
> > fail to populate for a certain mem section, print warning and its
> > ->section_mem_map will be cleared to cancel the marking of being present.
> > Like this, the number of mem sections marked as present could become
> > less during sparse_init() execution.
> > 
> > Here just defer the ms->section_mem_map clearing if failed to populate
> > its page tables until the last for_each_present_section_nr() loop. This
> > is in preparation for later optimizing the mem map allocation.
> > 
> > Signed-off-by: Baoquan He <bhe@...hat.com>
> > ---
> >  mm/sparse-vmemmap.c |  1 -
> >  mm/sparse.c         | 12 ++++++++----
> >  2 files changed, 8 insertions(+), 5 deletions(-)
> > 
> > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> > index bd0276d5f66b..640e68f8324b 100644
> > --- a/mm/sparse-vmemmap.c
> > +++ b/mm/sparse-vmemmap.c
> > @@ -303,7 +303,6 @@ void __init sparse_mem_maps_populate_node(struct page **map_map,
> >  		ms = __nr_to_section(pnum);
> >  		pr_err("%s: sparsemem memory map backing failed some memory will not be available\n",
> >  		       __func__);
> > -		ms->section_mem_map = 0;
> 
> Since we are deferring the clearing of section_mem_map, I guess we do not need
> 
> struct mem_section *ms;
> ms = __nr_to_section(pnum);
> 
> anymore, right?

Right, good catch, thanks.

I will post a new round to fix this.

> 
> >  	}
> >  
> >  	if (vmemmap_buf_start) {
> > diff --git a/mm/sparse.c b/mm/sparse.c
> > index 6314303130b0..71ad53da2cd1 100644
> > --- a/mm/sparse.c
> > +++ b/mm/sparse.c
> > @@ -451,7 +451,6 @@ void __init sparse_mem_maps_populate_node(struct page **map_map,
> >  		ms = __nr_to_section(pnum);
> >  		pr_err("%s: sparsemem memory map backing failed some memory will not be available\n",
> >  		       __func__);
> > -		ms->section_mem_map = 0;
> 
> The same goes here.
> 
> 
> 
> -- 
> Oscar Salvador
> SUSE L3