On Mon 04-11-19 16:51:26, Vincent Whitchurch wrote:
> On Thu, Oct 31, 2019 at 08:25:55AM +0100, Michal Hocko wrote:
> > On Wed 30-10-19 18:31:23, Michal Hocko wrote:
> > [...]
> > > 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;
> >
> > Vincent, could you give this a try please? It would be even better if
> > you could add some debugging to measure the overhead. Let me know if you
> > need any help with a debugging patch.
>
> I've tested this patch and it works on my platform: The allocations
> from sparse_buffer_alloc() now succeed and the fallback path is not
> taken.
Thanks a lot. I will try to prepare the full patch with a proper
changelog sometimes this week.
> I'm not sure what kind of overhead you're interested in.
The memory overhead when the sparsemap_buf PAGE_SIZE alignment is in
place. In other words (ptr - sparsemap_buf) in sparse_buffer_alloc. If
the sparsemap_buf was properly aligned then the diff should be 0.
--
Michal Hocko
SUSE Labs
