Messages in this thread | | | Date | Tue, 15 Nov 2011 16:28:36 -0800 | Subject | Re: [PATCH] mm: avoid livelock on !__GFP_FS allocations | From | Colin Cross <> |
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On Tue, Nov 15, 2011 at 4:22 PM, Minchan Kim <minchan.kim@gmail.com> wrote: > On Tue, Nov 15, 2011 at 05:36:56PM +0000, Mel Gorman wrote: >> 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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