Re: [RFC PATCH 2/2] mm/sparse: add last_section_nr in sparse_init() to reduce some iteration cycle

From: Tejun Heo
Date: Fri Feb 10 2017 - 21:28:02 EST


On Sat, Feb 11, 2017 at 10:18:29AM +0800, Wei Yang wrote:
> During the sparse_init(), it iterate on each possible section. On x86_64,
> it would always be (2^19) even there is not much memory. For example, on a
> typical 4G machine, it has only (2^5) to (2^6) present sections. This
> benefits more on a system with smaller memory.
> This patch calculates the last section number from the highest pfn and use
> this as the boundary of iteration.

* How much does this actually matter? Can you measure the impact?

* Do we really need to add full reverse iterator to just get the
highest section number?