Re: Improvement on memory subsystem

From: David Lang
Date: Mon Jul 24 2006 - 13:06:05 EST

On Mon, 24 Jul 2006, yunfeng zhang wrote:

How to let memory subsystem allocate bigger consecutive memory pages? In current
Linux, to driver programmer it's always failed to issue a request to alloc_pages
with a enough larger order parameter, or it's diffult to allocate a bigger
consecutive physical memory block.

The reason causing the problem, I think, are the items listed below
1) Core space has a static mapping relationship with physical memory pages. So
once a core page is allocated, its core address is also fixed, it prevents the
physical pages around it to conglomerate together.
2) Current physical page management arithmetic is buddy arithmetic. The main
advantage of its is that pages managed by it is always aligned by 2 power. But,
is it necessary or there is any hardware which need physical memory pages
aligned by 2 or more power?

The solution is
1) Using dynamic page mapping on core space. So we can move all core pages
freely anytime to conglomerate bigger consecutive memory pages, a new background
daemon thread -- RemapDaemon can do conglomeration periodly.

this gets discussed periodicly, however the performance hit of doing the mapping for all core memory accesses is something that the developers have not been willing to accept.

2) Using another page management arithmetic instead of buddy, the minimum unit
of new arithmetic should be page. In fact, I think dlmalloc arithmetic is a good
candidate, it's also page conglomeration-affinity.

experiment, if it's as good as you think it will be post the numbers an you will get a lot of attention. quite a few people are working on the memory allocation for various things, therea re a lot of useage patterns to balance (and avaid pathalogical problems with).

David Lang
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