* [PATCH] mm, sparse: do not waste pre allocated memmap space
@ 2019-11-19 9:26 Michal Hocko
2019-11-19 10:03 ` David Hildenbrand
0 siblings, 1 reply; 4+ messages in thread
From: Michal Hocko @ 2019-11-19 9:26 UTC (permalink / raw)
To: Andrew Morton
Cc: Pavel Tatashin, Vincent Whitchurch, Oscar Salvador,
David Hildenbrand, linux-mm, LKML, Michal Hocko
From: Michal Hocko <mhocko@suse.com>
Vincent has noticed [1] that there is something unusual with the memmap
allocations going on on his platform
: I noticed this because on my ARM64 platform, with 1 GiB of memory the
: first [and only] section is allocated from the zeroing path while with
: 2 GiB of memory the first 1 GiB section is allocated from the
: non-zeroing path.
The underlying problem is that although sparse_buffer_init allocates enough
memory for all sections on the node sparse_buffer_alloc is not able to
consume them due to mismatch in the expected allocation alignement.
While sparse_buffer_init preallocation uses the PAGE_SIZE alignment the
real memmap has to be aligned to section_map_size() this results in a
wasted initial chunk of the preallocated memmap and unnecessary fallback
allocation for a section.
While we are at it also change __populate_section_memmap to align to the
requested size because at least VMEMMAP has constrains to have memmap
properly aligned.
[1] http://lkml.kernel.org/r/20191030131122.8256-1-vincent.whitchurch@axis.com
Reported-and-debugged-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Fixes: 35fd1eb1e821 ("mm/sparse: abstract sparse buffer allocations")
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
mm/sparse.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/mm/sparse.c b/mm/sparse.c
index f6891c1992b1..079f3e3c4cab 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -458,8 +458,7 @@ struct page __init *__populate_section_memmap(unsigned long pfn,
if (map)
return map;
- map = memblock_alloc_try_nid(size,
- PAGE_SIZE, addr,
+ map = memblock_alloc_try_nid(size, size, addr,
MEMBLOCK_ALLOC_ACCESSIBLE, nid);
if (!map)
panic("%s: Failed to allocate %lu bytes align=0x%lx nid=%d from=%pa\n",
@@ -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);
sparsemap_buf_end = sparsemap_buf + size;
--
2.20.1
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] mm, sparse: do not waste pre allocated memmap space
2019-11-19 9:26 [PATCH] mm, sparse: do not waste pre allocated memmap space Michal Hocko
@ 2019-11-19 10:03 ` David Hildenbrand
2019-11-19 22:10 ` Andrew Morton
0 siblings, 1 reply; 4+ messages in thread
From: David Hildenbrand @ 2019-11-19 10:03 UTC (permalink / raw)
To: Michal Hocko, Andrew Morton
Cc: Pavel Tatashin, Vincent Whitchurch, Oscar Salvador, linux-mm,
LKML, Michal Hocko
On 19.11.19 10:26, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
>
> Vincent has noticed [1] that there is something unusual with the memmap
> allocations going on on his platform
> : I noticed this because on my ARM64 platform, with 1 GiB of memory the
> : first [and only] section is allocated from the zeroing path while with
> : 2 GiB of memory the first 1 GiB section is allocated from the
> : non-zeroing path.
>
> The underlying problem is that although sparse_buffer_init allocates enough
> memory for all sections on the node sparse_buffer_alloc is not able to
> consume them due to mismatch in the expected allocation alignement.
> While sparse_buffer_init preallocation uses the PAGE_SIZE alignment the
> real memmap has to be aligned to section_map_size() this results in a
> wasted initial chunk of the preallocated memmap and unnecessary fallback
> allocation for a section.
>
> While we are at it also change __populate_section_memmap to align to the
> requested size because at least VMEMMAP has constrains to have memmap
> properly aligned.
>
> [1] http://lkml.kernel.org/r/20191030131122.8256-1-vincent.whitchurch@axis.com
> Reported-and-debugged-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
> Fixes: 35fd1eb1e821 ("mm/sparse: abstract sparse buffer allocations")
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
> mm/sparse.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index f6891c1992b1..079f3e3c4cab 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -458,8 +458,7 @@ struct page __init *__populate_section_memmap(unsigned long pfn,
> if (map)
> return map;
>
> - map = memblock_alloc_try_nid(size,
> - PAGE_SIZE, addr,
> + map = memblock_alloc_try_nid(size, size, addr,
> MEMBLOCK_ALLOC_ACCESSIBLE, nid);
> if (!map)
> panic("%s: Failed to allocate %lu bytes align=0x%lx nid=%d from=%pa\n",
> @@ -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 :)
> sparsemap_buf_end = sparsemap_buf + size;
>
Acked-by: David Hildenbrand <david@redhat.com>
--
Thanks,
David / dhildenb
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] mm, sparse: do not waste pre allocated memmap space
2019-11-19 10:03 ` David Hildenbrand
@ 2019-11-19 22:10 ` Andrew Morton
2019-11-20 7:52 ` Michal Hocko
0 siblings, 1 reply; 4+ messages in thread
From: Andrew Morton @ 2019-11-19 22:10 UTC (permalink / raw)
To: David Hildenbrand
Cc: Michal Hocko, Pavel Tatashin, Vincent Whitchurch, Oscar Salvador,
linux-mm, LKML, Michal Hocko
On Tue, 19 Nov 2019 11:03:58 +0100 David Hildenbrand <david@redhat.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;
}
_
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] mm, sparse: do not waste pre allocated memmap space
2019-11-19 22:10 ` Andrew Morton
@ 2019-11-20 7:52 ` Michal Hocko
0 siblings, 0 replies; 4+ messages in thread
From: Michal Hocko @ 2019-11-20 7:52 UTC (permalink / raw)
To: Andrew Morton
Cc: David Hildenbrand, Pavel Tatashin, Vincent Whitchurch,
Oscar Salvador, linux-mm, LKML
On Tue 19-11-19 14:10:47, Andrew Morton wrote:
> On Tue, 19 Nov 2019 11:03:58 +0100 David Hildenbrand <david@redhat.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;
> }
I didn't bother mostly because the creative code layout made the
intention of the patch more obvious. But if it saves from nightmares
then why not.
--
Michal Hocko
SUSE Labs
^ permalink raw reply [flat|nested] 4+ messages in thread
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2019-11-19 9:26 [PATCH] mm, sparse: do not waste pre allocated memmap space Michal Hocko
2019-11-19 10:03 ` David Hildenbrand
2019-11-19 22:10 ` Andrew Morton
2019-11-20 7:52 ` Michal Hocko
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