lkml.org 
[lkml]   [2009]   [Nov]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
Subjectusing highmem for atomic copy of lowmem was Re: [PATCHv2 2/5] vmscan: Kill hibernation specific reclaim logic and unify it
Hi!

> > >> (Disclaimer: I don't think about highmem a lot any more, and might have
> > >> forgotten some of the details, or swsusp's algorithms might have
> > >> changed. Rafael might need to correct some of this...)
> > >>
> > >> Imagine that you have a system with 1000 pages of lowmem and 5000 pages
> > >> of highmem. Of these, 950 lowmem pages are in use and 500 highmem pages
> > >> are in use.
> > >>
> > >> In order to to be able to save an image, we need to be able to do an
> > >> atomic copy of those lowmem pages.
> > >>
> > >> You might think that we could just copy everything into the spare
> > >> highmem pages, but we can't because mapping and unmapping the highmem
> > >> pages as we copy the data will leave us with an inconsistent copy.
> > >
> > > This isn't the case any more for the mainline hibernate code. We use highmem
> > > for storing image data as well as lowmem.
> >
> > Highmem for storing copies of lowmem pages?
>
> It is possible in theory, but I don't think it happens in practice given the
> way in which the memory is freed. Still copy_data_page() takes this
> possibility into account.

Yes, it does, but I wonder if it can ever work...?

copy_data_page() takes great care not to modify any memory -- like
using handmade loop instead of memcpy() -- yet it uses kmap_atomic()
and friends.

If kmap_atomic()+kunmap_atomic() pair is guaranteed not to change any
memory, thats probably safe, but...

(Actually, plain memcpy() should be usable for copying highmem pages;
those should not contain task_structs or anything else touched by
memcpy()).
Pavel

--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html


\
 
 \ /
  Last update: 2009-11-13 00:23    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site