lkml.org 
[lkml]   [2019]   [Oct]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Date
SubjectRe: [PATCH] mm/sparse: Consistently do not zero memmap
On Wed, Oct 30, 2019 at 1:31 PM Michal Hocko <mhocko@kernel.org> wrote:
>
> On Wed 30-10-19 12:53:41, Pavel Tatashin wrote:
> > On Wed, Oct 30, 2019 at 11:31 AM Michal Hocko <mhocko@kernel.org> wrote:
> > >
> > > On Wed 30-10-19 11:20:44, Pavel Tatashin wrote:
> > > > On Wed, Oct 30, 2019 at 10:13 AM Michal Hocko <mhocko@kernel.org> wrote:
> > > > >
> > > > > [Add Pavel - the email thread starts http://lkml.kernel.org/r/20191030131122.8256-1-vincent.whitchurch@axis.com
> > > > > but it used your old email address]
> > > > >
> > > > > On Wed 30-10-19 15:02:16, Vincent Whitchurch wrote:
> > > > > > On Wed, Oct 30, 2019 at 02:29:58PM +0100, Michal Hocko wrote:
> > > > > > > On Wed 30-10-19 14:11:22, Vincent Whitchurch wrote:
> > > > > > > > (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.)
> > > > > > >
> > > > > > > Do I get it right that sparse_buffer_init couldn't allocate memmap for
> > > > > > > the full node for some reason and so sparse_init_nid would have to
> > > > > > > allocate one for each memory section?
> > > > > >
> > > > > > Not quite. The sparsemap_buf is successfully allocated with the correct
> > > > > > size in sparse_buffer_init(), but sparse_buffer_alloc() fails to
> > > > > > allocate the same size from it.
> > > > > >
> > > > > > The reason it fails is that sparse_buffer_alloc() for some reason wants
> > > > > > to return a pointer which is aligned to the allocation size. But the
> > > > > > sparsemap_buf was only allocated with PAGE_SIZE alignment so there's not
> > > > > > enough space to align it.
> > > > > >
> > > > > > I don't understand the reason for this alignment requirement since the
> > > > > > fallback path also allocates with PAGE_SIZE alignment. I'm guessing the
> > > > > > alignment is for the VMEMAP code which also uses sparse_buffer_alloc()?
> > > > >
> > > > > I am not 100% sure TBH. Aligning makes some sense when mapping the
> > > > > memmaps to page tables but that would suggest that sparse_buffer_init
> > > > > is using a wrong alignment then. It is quite wasteful to allocate
> > > > > alarge misaligned block like that.
> > > > >
> > > > > Your patch still makes sense but this is something to look into.
> > > > >
> > > > > Pavel?
> > > >
> > > > I remember thinking about this large alignment, as it looked out of
> > > > place to me also.
> > > > It was there to keep memmap in single chunks on larger x86 machines.
> > > > Perhaps it can be revisited now.
> > >
> > > Don't we need 2MB aligned memmaps for their PMD mappings?
> >
> > Yes, PMD_SIZE should be the alignment here. It just does not make
> > sense to align to size.
>
> What about this? It still aligns to the size but that should be
> correctly done to the section size level.
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 72f010d9bff5..ab1e6175ac9a 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -456,8 +456,7 @@ 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",
> @@ -474,8 +473,13 @@ 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;

This looks good, I think we should also change alignment in fallback
of vmemmap_alloc_block() to be
section_map_size().

+++ b/mm/sparse-vmemmap.c
@@ -65,9 +65,10 @@ void * __meminit vmemmap_alloc_block(unsigned long
size, int node)
warned = true;
}
return NULL;
- } else
- return __earlyonly_bootmem_alloc(node, size, size,
+ } else {
+ return __earlyonly_bootmem_alloc(node, size, section_map_size(),
__pa(MAX_DMA_ADDRESS));
+ }
}

Pasha

>
> --
> Michal Hocko
> SUSE Labs

\
 
 \ /
  Last update: 2019-10-30 18:54    [W:0.181 / U:0.624 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site