linux-kernel - Re: [PATCH v5 0/4] mm/sparse: Optimize memmap allocation during sparse

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Message-ID: <CAGM2reYKn80fn8Nb_AT4ybVih4c7cd8+U1nDfJ-C0fwM+DB4jw@mail.gmail.com>
Date:   Wed, 27 Jun 2018 13:47:28 -0400
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     bhe@...hat.com
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        dave.hansen@...el.com, pagupta@...hat.com,
        Linux Memory Management List <linux-mm@...ck.org>,
        kirill.shutemov@...ux.intel.com
Subject: Re: [PATCH v5 0/4] mm/sparse: Optimize memmap allocation during sparse_init()

This work made me think why do we even have
CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER ? This really should be the
default behavior for all systems. Yet, it is enabled only on x86_64.
We could clean up an already messy sparse.c if we removed this config,
and enabled its path for all arches. We would not break anything
because if we cannot allocate one large mmap_map we still fallback to
allocating a page at a time the same as what happens when
CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER=n.

Pavel