On Tue, Nov 15, 2011 at 4:22 PM, Minchan Kim <minchan.kim@xxxxxxxxx> 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 > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>