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

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Date:   Sun, 1 Jul 2018 23:28:01 -0400
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     bhe@...hat.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()

> > 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.
>

I do not see how  we can succeed after the first failure. We still
allocate from the same node:

sparse_mem_map_populate() may fail only if we could not allocate large
enough buffer vmemmap_buf_start earlier.

This means that in:
sparse_mem_map_populate()
  vmemmap_populate()
    vmemmap_populate_hugepages()
      vmemmap_alloc_block_buf() (no buffer, so call allocator)
        vmemmap_alloc_block(size, node);
            __earlyonly_bootmem_alloc(node, size, size, __pa(MAX_DMA_ADDRESS));
              memblock_virt_alloc_try_nid_raw() -> Nothing changes for
this call to succeed. So, all consequent calls to
sparse_mem_map_populate() in this node will fail as well.

> >
> Forgot mentioning it's the vervion in mm/sparse-vmemmap.c

Sorry, I do not understand what is vervion.

Thank you,
Pavel