linux-kernel - Re: [PATCH v5 1/5] mm/sparse: abstract sparse buffer allocations

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Date:   Fri, 13 Jul 2018 15:17:49 +0200
From:   Oscar Salvador <osalvador@...hadventures.net>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        kirill.shutemov@...ux.intel.com, mhocko@...e.com,
        linux-mm@...ck.org, dan.j.williams@...el.com, jack@...e.cz,
        jglisse@...hat.com, jrdr.linux@...il.com, bhe@...hat.com,
        gregkh@...uxfoundation.org, vbabka@...e.cz,
        richard.weiyang@...il.com, dave.hansen@...el.com,
        rientjes@...gle.com, mingo@...nel.org, abdhalee@...ux.vnet.ibm.com,
        mpe@...erman.id.au
Subject: Re: [PATCH v5 1/5] mm/sparse: abstract sparse buffer allocations

On Thu, Jul 12, 2018 at 04:37:26PM -0400, Pavel Tatashin wrote:
> +static void *sparsemap_buf __meminitdata;
> +static void *sparsemap_buf_end __meminitdata;
> +
> +void __init sparse_buffer_init(unsigned long size, int nid)
> +{
> +	BUG_ON(sparsemap_buf);

Why do we need a BUG_ON() here?
Looking at the code I cannot really see how we can end up with sparsemap_buf being NULL.
Is it just for over-protection?

> +	sparsemap_buf =
> +		memblock_virt_alloc_try_nid_raw(size, PAGE_SIZE,
> +						__pa(MAX_DMA_ADDRESS),
> +						BOOTMEM_ALLOC_ACCESSIBLE, nid);

In your previous version, you didn't pass a required alignment when setting up sparsemap_buf.
size is already PMD_SIZE aligned, do we need to align it also to PAGE_SIZE?

Thanks
-- 
Oscar Salvador
SUSE L3