Re: [RFC][PATCH] swsusp: support creating bigger images

Pavel Machek
2006-04-25T20:33:38Z

Hi!

> > > -unsigned int count_data_pages(void)
> > > +/**
> > > + * need_to_copy - determine if a page needs to be copied before saving.
> > > + * Returns false if the page can be saved without copying.
> > > + */
> > > +
> > > +static int need_to_copy(struct page *page)
> > > +{
> > > + if (!PageLRU(page) || PageCompound(page))
> > > + return 1;
> > > + if (page_mapped(page))
> > > + return page_mapped_by_current(page);
> > > +
> > > + return 1;
> > > +}
> >
> > I'd much rather VM internal type stuff get moved *out* of kernel/power :(
>
> Well, I kind of agree, but I don't know where to place it under mm/.
>
> > It needs more comments too. Also, how important is it for the page to be
> > off the LRU?
>
> Hm, I'm not sure if that's what you're asking about, but the pages off the LRU
> are handled in a usual way, ie. copied when snapshotting the system. The
> pages _on_ the LRU may be included in the snapshot image without
> copying, but I require them additionally to be (a) mapped by someone and
> (b) not mapped by the current task.

Why do you _want_ them mapped by someone?

> > b) Why are you clearing PageLRU outside the spinlock?
>
> Well, good question. ;-) Moreover it seems I don't need to acquire the
> spinlock at all, because this is done on one CPU with IRQs disabled and the
> other tasks frozen.

Well, it is probably better to still take the spinlock. That way, if
something goes wrong we get deadlock, not anything worse.
Pavel
--
Thanks for all the (sleeping) penguins.