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

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Date:   Thu, 12 Jul 2018 15:45:52 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        linux-kernel@...r.kernel.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,
        osalvador@...hadventures.net, abdhalee@...ux.vnet.ibm.com,
        mpe@...erman.id.au
Subject: Re: [PATCH v5 1/5] mm/sparse: abstract sparse buffer allocations

On Thu, 12 Jul 2018 16:37:26 -0400 Pavel Tatashin <pasha.tatashin@...cle.com> wrote:

> When struct pages are allocated for sparse-vmemmap VA layout, we first
> try to allocate one large buffer, and than if that fails allocate struct
> pages for each section as we go.
> 
> The code that allocates buffer is uses global variables and is spread
> across several call sites.
> 
> Cleanup the code by introducing three functions to handle the global
> buffer:
> 
> sparse_buffer_init()	initialize the buffer
> sparse_buffer_fini()	free the remaining part of the buffer
> sparse_buffer_alloc()	alloc from the buffer, and if buffer is empty
> return NULL
> 
> Define these functions in sparse.c instead of sparse-vmemmap.c because
> later we will use them for non-vmemmap sparse allocations as well.
> 
> ...
>
> +void * __meminit sparse_buffer_alloc(unsigned long size)
> +{
> +	void *ptr = NULL;
> +
> +	if (sparsemap_buf) {
> +		ptr = (void *)ALIGN((unsigned long)sparsemap_buf, size);
> +		if (ptr + size > sparsemap_buf_end)
> +			ptr = NULL;
> +		else
> +			sparsemap_buf = ptr + size;
> +	}
> +	return ptr;
> +}

tweak...

diff -puN mm/sparse.c~mm-sparse-abstract-sparse-buffer-allocations-fix mm/sparse.c
--- a/mm/sparse.c~mm-sparse-abstract-sparse-buffer-allocations-fix
+++ a/mm/sparse.c
@@ -491,7 +491,7 @@ void * __meminit sparse_buffer_alloc(uns
 	void *ptr = NULL;
 
 	if (sparsemap_buf) {
-		ptr = (void *)ALIGN((unsigned long)sparsemap_buf, size);
+		ptr = PTR_ALIGN(sparsemap_buf, size);
 		if (ptr + size > sparsemap_buf_end)
 			ptr = NULL;
 		else