linux-kernel - Re: [PATCH v3 1/2] mm/sparse: add sparse_init

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Message-ID: <20180702031417.GP3223@MiWiFi-R3L-srv>
Date:   Mon, 2 Jul 2018 11:14:17 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     Steven Sistare <steven.sistare@...cle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kirill.shutemov@...ux.intel.com, Michal Hocko <mhocko@...e.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        dan.j.williams@...el.com, jack@...e.cz, jglisse@...hat.com,
        Souptick Joarder <jrdr.linux@...il.com>,
        gregkh@...uxfoundation.org, Vlastimil Babka <vbabka@...e.cz>,
        Wei Yang <richard.weiyang@...il.com>, dave.hansen@...el.com,
        rientjes@...gle.com, mingo@...nel.org, osalvador@...hadventures.net
Subject: Re: [PATCH v3 1/2] mm/sparse: add sparse_init_nid()

On 07/01/18 at 11:03pm, Pavel Tatashin wrote:
> > Ah, yes, I misunderstood it, sorry for that.
> >
> > Then I have only one concern, for vmemmap case, if one section doesn't
> > succeed to populate its memmap, do we need to skip all the remaining
> > sections in that node?
> 
> Yes, in sparse_populate_node() we have the following:
> 
> 294         for (pnum = pnum_begin; map_index < map_count; pnum++) {
> 295                 if (!present_section_nr(pnum))
> 296                         continue;
> 297                 if (!sparse_mem_map_populate(pnum, nid, NULL))
> 298                         break;
> 
> So, on the first failure, we even stop trying to populate other
> sections. No more memory to do so.

This is the thing I worry about. In old sparse_mem_maps_populate_node()
you can see, when not present or failed to populate, just continue. This
is the main difference between yours and the old code. The key logic is
changed here.

void __init sparse_mem_maps_populate_node(struct page **map_map,
                                          unsigned long pnum_begin,
                                          unsigned long pnum_end,
                                          unsigned long map_count, int nodeid)
{
	...
	for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
                struct mem_section *ms;

                if (!present_section_nr(pnum))
                        continue;

                map_map[pnum] = sparse_mem_map_populate(pnum, nodeid, NULL);
                if (map_map[pnum])                                                                                                                
                        continue;
                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;
        }
	...
}