linux-kernel - Re: [PATCH] mm, sparse: do not waste pre allocated memmap space

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Message-Id: <20191119141047.a8e31e95b631e28f84dc0bc9@linux-foundation.org>
Date:   Tue, 19 Nov 2019 14:10:47 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        Oscar Salvador <OSalvador@...e.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH] mm, sparse: do not waste pre allocated memmap space

On Tue, 19 Nov 2019 11:03:58 +0100 David Hildenbrand <david@...hat.com> wrote:

> > @@ -482,8 +481,13 @@ static void __init sparse_buffer_init(unsigned long size, int nid)
> >   {
> >   	phys_addr_t addr = __pa(MAX_DMA_ADDRESS);
> >   	WARN_ON(sparsemap_buf);	/* forgot to call sparse_buffer_fini()? */
> > +	/*
> > +	 * Pre-allocated buffer is mainly used by __populate_section_memmap
> > +	 * and we want it to be properly aligned to the section size - this is
> > +	 * especially the case for VMEMMAP which maps memmap to PMDs
> > +	 */
> >   	sparsemap_buf =
> > -		memblock_alloc_try_nid_raw(size, PAGE_SIZE,
> > +		memblock_alloc_try_nid_raw(size, section_map_size(),
> >   						addr,
> >   						MEMBLOCK_ALLOC_ACCESSIBLE, nid);
> 
> Wow, that alignment/layout gives me nightmares  ^
> 
> None of your business, though :)

We're allowed to change it ;)

--- a/mm/sparse.c~mm-sparse-do-not-waste-pre-allocated-memmap-space-fix
+++ a/mm/sparse.c
@@ -486,10 +486,8 @@ static void __init sparse_buffer_init(un
 	 * and we want it to be properly aligned to the section size - this is
 	 * especially the case for VMEMMAP which maps memmap to PMDs
 	 */
-	sparsemap_buf =
-		memblock_alloc_try_nid_raw(size, section_map_size(),
-						addr,
-						MEMBLOCK_ALLOC_ACCESSIBLE, nid);
+	sparsemap_buf = memblock_alloc_try_nid_raw(size, section_map_size(),
+					addr, MEMBLOCK_ALLOC_ACCESSIBLE, nid);
 	sparsemap_buf_end = sparsemap_buf + size;
 }
 
_