Re: [PATCH 0/5] Swapless page migration V2: Overview

[Lee Schermerhorn <Lee.Schermerhorn@hp.com>]

On Thu, 2006-04-13 at 17:27 -0700, Christoph Lameter wrote:
> On Thu, 13 Apr 2006, Andrew Morton wrote:
> 
> > > Currently page migration is depending on the ability to assign swap entries
> > > to pages. However, those entries will only be to identify anonymous pages.
> > > Page migration will not work without swap although swap space is never
> > > really used.
> > 
> > That strikes me as a fairly minor limitation?
> 
> Some people want never ever to use swap. Systems that have no swap defined 
> will currently not be able to migrate pages. Its kind of difficult to 
> comprehend that you need to have swap for migration, but then its not 
> going to be used. 
> 
> > > The patchset will allow later patches to enable migration of VM_LOCKED vmas,
> > > the ability to exempt vmas from page migration, and allow the implementation
> > > of a another userland migration API for handling batches of pages.
> > 
> > These seem like more important justifications.  Would you agree with that
> > judgement?
> 
> The swapless thing is the most important for us because many of our 
> customers do not have swap setup. Then follow the above 
> features then the efficiency consideration.

I do have the migration cache working against 17-rc1-mm2.  I tried to
address Christoph's prior comments.  I just haven't posted yet, as I was
working the migrate-on-fault/auto-migration series.  If one accepts lazy
migration, then the migration cache becomes more important because anon
pages can/will stay in the swap cache until the page is finally freed
[or maybe gets evicted from the swap cache?].

The migration cache still uses the swap infrastructure, so must
configure SWAP.  But, no swap devices need be configured.  Should
address that particular concern w/o major surgery to the existing
migration code.  

 Let me know if I should repost the patches.  Meanwhile, they're
available at:  
http://free.linux.hp.com/~lts/Patches/PageMigration/ [which seems
temporarily, I hope, unavailable].  Look for the migcache tarball.

Lee


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