Re: [PATCH 3/3][Fix] swsusp: prevent swsusp from failing if there's too many pagedir pages

[Pavel Machek <pavel@ucw.cz>]

Hi!

> > > > Lets see...
> > > > 
> > > > for i386, we have 768 pagedir entries. Each pagedir entry points to
> > > > page with 1023 pointers to pages. That means that up-to 768*1023*4096
> > > > bytes image can be saved to swap ~= 768 * 1K * 4K ~= 3 GB. That's more
> > > > than enough for i386.
> > > > 
> > > > for x86-64, we can have 128 pagedir entries (could not we fit more
> > > > there? 384 entries should fit, no?).
> > > 
> > > Yes.  To be exact, 460.
> > > 
> > > > Each pagedir entry has 511 pointers to pages (IIRC)...
> > > 
> > > 512, I think.
> > 
> > Okay, can we do simple solution where we put 460 there, plus a check
> > if it overflows (printk, abort suspend), for now? That should fix
> > 768MB machine...
> 
> For now: a constant in power.h depending on sizeof(long) and PAGE_SIZE,
> the size of swsusp_info.pagedir[] depending on it and the overflow check
> in write_pagedir()?

Yes, that would be very nice.

> Unfortunately it's not enough for what I'm cooking (think of resuming in 35 sec.
> to a fully responsive system - well, that's on my box).  A preliminary patch
> is at http://www.sisk.pl/kernel/patches/2.6.14-rc2-git3/swsusp-improve-freeing-memory.patch

Okay, I see, nice... We want to support that in future. (Actually it
is last piece of puzzle for swsusp3).

> > No, they probably will not be consecutive.
> > 
> > OTOH pagedirs are stored as a link list in memory already. Maybe we
> > should be able to extend that link list for a disk, too, with minimal
> > fuss? ...we'd have to write pagedir _backwards_ for that to work,
> > probably not nice, and swap_free() would really like direct access.
> 
> We write the pagedir after we have written the image, so the address
> field of each entry is not needed at that time, except for freeing the
> image memory in case of failure (with the "rework image freeing patch"
> they are not needed at all).  Thus potentially we can use the address
> fields of pagedir entries to link the pages on the swap.

I plan to push "rework image freeing patch" for other reasons,
too. I'd like to run longer tests on it, but so far it looks okay.

								Pavel
-- 
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