Re: [PATCH] Avoiding fragmentation through different allocator

[Marcelo Tosatti <marcelo.tosatti@cyclades.com>]

On Thu, Jan 20, 2005 at 10:13:00AM +0000, Mel Gorman wrote:
> Changelog since V5
> o Fixed up gcc-2.95 errors
> o Fixed up whitespace damage
> 
> Changelog since V4
> o No changes. Applies cleanly against 2.6.11-rc1 and 2.6.11-rc1-bk6. Applies
>   with offsets to 2.6.11-rc1-mm1
> 
> Changelog since V3
> o inlined get_pageblock_type() and set_pageblock_type()
> o set_pageblock_type() now takes a zone parameter to avoid a call to page_zone()
> o When taking from the global pool, do not scan all the low-order lists
> 
> Changelog since V2
> o Do not to interfere with the "min" decay
> o Update the __GFP_BITS_SHIFT properly. Old value broke fsync and probably
>   anything to do with asynchronous IO
>   
> Changelog since V1
> o Update patch to 2.6.11-rc1
> o Cleaned up bug where memory was wasted on a large bitmap
> o Remove code that needed the binary buddy bitmaps
> o Update flags to avoid colliding with __GFP_ZERO changes
> o Extended fallback_count bean counters to show the fallback count for each
>   allocation type
> o In-code documentation

Hi Mel,

I was thinking that it would be nice to have a set of high-order intensive workloads, 
and I wonder what are the most common high-order allocation paths which fail.

It mostly depends on hardware because most high-order allocations happen inside
device drivers? What are the kernel codepaths which try to do high-order allocations
and fallback if failed? 

To measure whether the cost of page migration offsets the ability to be able to deliver
high-order allocations we want a set of meaningful performance tests?

Its quite possible that not all unsatisfiable high-order allocations want to 
force page migration (which is quite expensive in terms of CPU/cache). Only migrate on 
__GFP_NOFAIL ?

William, that same tradeoff exists for the zone balancing through migration idea
you propose...