On Tue, Nov 15, 2011 at 4:22 PM, Minchan Kim [off-list ref] wrote:

On Tue, Nov 15, 2011 at 05:36:56PM +0000, Mel Gorman wrote:

quoted

On Wed, Nov 16, 2011 at 01:13:30AM +0900, Minchan Kim wrote:
The impact would be that during the time between processes been frozen
and storage being suspended, GFP_NOIO allocations that used to call
wait_iff_congested and retry while kswapd does its thing will return
failure instead. These GFP_NOIO allocations that used to succeed will
now fail in rare cases during suspend and I don't think we want that.

Is this what you meant or had you something else in mind?

You read my mind exactly!

I thought hibernation process is as follows,

freeze user processes
oom_disable
hibernate_preallocate_memory
freeze kernel processes(include kswapd)
pm_restrict_gfp_mask
swsusp_save

My guessing is hibernate_prealocate_memory should reserve all memory needed
for hibernation for reclaimaing pages of kswapd because kswapd just would be
stopped so during swsusp_save, page reclaim should not be occured.

But being see description of patch, my guess seems wrong.
Now the problem happens and it means page reclaim happens during swsusp_save.
Colin or someone could confirm this?

The problem I see is during suspend, not hibernation.  The particular
allocation that usually causes the problem is the pgd_alloc for page
tables when re-enabling the 2nd cpu during resume, which is odd as
those same page tables were freed during suspend.  I guess an
unfreezable kernel thread allocated that memory between the free and
re-allocation.

If so, could we reserve more memory when we preallocate hibernation memory
for avoiding page reclaim without kswapd?

--
Kind regards,
Minchan Kim

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