Re: [PATCH] mm: page_alloc: Skip over regions of invalid pfns where possible

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 10 Jan 2017 23:37:53 +0000 James Hartley <james.hartley@imgtec.com> wrote:

> 
> On 06/01/17 22:43, Andrew Morton wrote:
> > On Fri, 25 Nov 2016 18:55:18 +0000 Paul Burton <paul.burton@imgtec.com> wrote:
> >
> >> When using a sparse memory model memmap_init_zone() when invoked with
> >> the MEMMAP_EARLY context will skip over pages which aren't valid - ie.
> >> which aren't in a populated region of the sparse memory map. However if
> >> the memory map is extremely sparse then it can spend a long time
> >> linearly checking each PFN in a large non-populated region of the memory
> >> map & skipping it in turn.
> >>
> >> When CONFIG_HAVE_MEMBLOCK_NODE_MAP is enabled, we have sufficient
> >> information to quickly discover the next valid PFN given an invalid one
> >> by searching through the list of memory regions & skipping forwards to
> >> the first PFN covered by the memory region to the right of the
> >> non-populated region. Implement this in order to speed up
> >> memmap_init_zone() for systems with extremely sparse memory maps.
> > Could we have a changelog which includes some timing measurements? 
> > That permits others to understand the value of this patch.
> >
> I have tested this patch on a virtual model of a Samurai CPU with a
> sparse memory map.  The kernel boot time drops from 109 to 62 seconds. 

Thanks.  Nice.  I updated the changelog.

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