Re: Which is simpler? (Was Re: [Suspend2-devel] Re: [ 00/10] [Suspend2] Modules support.)

[Nigel Cunningham <ncunningham@cyclades.com>]

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On Friday 24 February 2006 08:37, Rafael J. Wysocki wrote:
> Hi,
>
> On Thursday 23 February 2006 13:17, Pavel Machek wrote:
> > > > Ok, I have no problems with visions.
> > > >
> > > > > I think we should try to get the pagecache stuff right first
> > > > > anyway.
> > > >
> > > > Are you sure it is worth doing? I mean... it only helps on small
> > > > machines, no?
> > > >
> > > > OTOH having it for benchmarks will be nice, and perhaps we could use
> > > > that kind it to speed up boot and similar things...
> > >
> > > Currently some people can't suspend with the mainline code because it
> > > cannot free as much memory as needed on their boxes.  I think we should
> > > care for them too.
> >
> > But saving pagecache will not help them *at all*!
> >
> > [Because pagecache is freeable, anyway, so it will be freed. Now... I
> > have seen some problems where free_some_memory did not free enough,
> > and schedule()/retry helped a bit... that probably should be fixed.]
>
> It seems I need to understand correctly what the difference between what
> we do and what Nigel does is.  I thought the Nigel's approach was to save
> some cache pages to disk first and use the memory occupied by them to
> store the image data.  If so, is the page cache involved in that or
> something else?

You're right. The only point I would query is that I'm not sure on terminology 
- whether 'page cache' == LRU. In case there's any difference, I'll say that 
I treat pages on the active and inactive LRU lists separately, saving them to 
disk first and using the memory occupied by them for the atomic copy (with 
the exception, of course, of pages belonging to processes such as userui - 
these are made part of the atomic copy and not overwritten).

Regards,

Nigel

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