> On Wednesday, September 01, 2010, KOSAKI Motohiro wrote:
quoted text
> > > === 8< ===
> > > PM: Marking nosave pages: ...0009f000 - ...000100000
> > > PM: basic memory bitmaps created
> > > PM: Syncing filesystems ... done
> > > Freezing user space processes ... (elapsed 0.01 seconds) done.
> > > Freezing remaining freezable tasks ... (elapsed 0.01 seconds) done.
> > > PM: Preallocating image memory...
> > > shrink_all_memory start
> > > PM: shrink memory: pass=1, req:310171 reclaimed:15492 free:360936
> > > PM: shrink memory: pass=2, req:294679 reclaimed:28864 free:373981
> > > PM: shrink memory: pass=3, req:265815 reclaimed:60311 free:405374
> > > PM: shrink memory: pass=4, req:205504 reclaimed:97870 free:443024
> > > PM: shrink memory: pass=5, req:107634 reclaimed:146948 free:492141
> > > shrink_all_memory: req:107634 reclaimed:146948 free:492141
> > > PM: preallocate_image_highmem 556658 278329
> > > PM: preallocate_image_memory 103139 103139
> > > PM: preallocate_highmem_fraction 183908 556658 760831 -> 183908
> > > === >8 ===
> > 
> > Rafael, this log mean hibernate_preallocate_memory() has a bug.
> 
> Well, it works as designed ...
> 
> > It allocate memory as following order.
> >  1. preallocate_image_highmem()  (i.e. __GFP_HIGHMEM)
> >  2. preallocate_image_memory()   (i.e. GFP_KERNEL)
> >  3. preallocate_highmem_fraction (i.e. __GFP_HIGHMEM)
> >  4. preallocate_image_memory()   (i.e. GFP_KERNEL)
> > 
> > But, please imazine following scenario (as Vefa's scenario).
> >  - system has 3GB memory. 1GB is normal. 2GB is highmem.
> >  - all normal memory is free
> >  - 1.5GB memory of highmem are used for tmpfs. rest 500MB is free.
> 
> Indeed, that's a memory allocation pattern I didn't anticipate.
> 
> > At that time, hibernate_preallocate_memory() works as following.
> > 
> > 1. call preallocate_image_highmem(1GB)
> > 2. call preallocate_image_memory(500M)		total 1.5GB allocated
> > 3. call preallocate_highmem_fraction(660M)	total 2.2GB allocated
> > 
> > then, all of normal zone memory was exhaust. next preallocate_image_memory()
> > makes OOM, and oom_killer_disabled makes infinite loop.
> > (oom_killer_disabled careless is vmscan bug. I'll fix it soon)
> 
> So, it looks like the problem will go away if we check if there are any normal
> pages to allocate from before calling the last preallocate_image_memory()?
> 
> Like in the patch below, perhaps?

Looks like fine. but I have one question. hibernate_preallocate_memory() call
preallocate_image_memory() two times. Why do you only care latter one?
former one seems similar risk.


quoted text
> > The problem is, alloc_pages(__GFP_HIGHMEM) -> alloc_pages(GFP_KERNEL) is
> > wrong order. alloc_pages(__GFP_HIGHMEM) may allocate page from lower zone.
> > then, next alloc_pages(GFP_KERNEL) lead to OOM.
> > 
> > Please consider alloc_pages(GFP_KERNEL) -> alloc_pages(__GFP_HIGHMEM) order.
> > Even though vmscan fix can avoid infinite loop, OOM situation might makes
> > big slow down on highmem machine. It seems no good.
> 
> There's a problem with the ordering change that it wouldn't be clear how many
> pages to request from the normal zone in step 1 and 3.

ok, I see. thanks for good correction my mistake.




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