On Tue, Oct 25, 2011 at 02:26:56AM -0700, Colin Cross wrote: > On Tue, Oct 25, 2011 at 2:09 AM, Mel Gorman <mgorman@xxxxxxx> wrote: > > On Mon, Oct 24, 2011 at 11:39:49PM -0700, Colin Cross wrote: > >> Under the following conditions, __alloc_pages_slowpath can loop > >> forever: > >> gfp_mask & __GFP_WAIT is true > >> gfp_mask & __GFP_FS is false > >> reclaim and compaction make no progress > >> order <= PAGE_ALLOC_COSTLY_ORDER > >> > >> These conditions happen very often during suspend and resume, > >> when pm_restrict_gfp_mask() effectively converts all GFP_KERNEL > >> allocations into __GFP_WAIT. > > b> > >> The oom killer is not run because gfp_mask & __GFP_FS is false, > >> but should_alloc_retry will always return true when order is less > >> than PAGE_ALLOC_COSTLY_ORDER. > >> > >> Fix __alloc_pages_slowpath to skip retrying when oom killer is > >> not allowed by the GFP flags, the same way it would skip if the > >> oom killer was allowed but disabled. > >> > >> Signed-off-by: Colin Cross <ccross@xxxxxxxxxxx> > > > > Hi Colin, > > > > Your patch functionally seems fine. I see the problem and we certainly > > do not want to have the OOM killer firing during suspend. I would prefer > > that the IO devices would not be suspended until reclaim was completed > > but I imagine that would be a lot harder. > > > > That said, it will be difficult to remember why checking __GFP_NOFAIL in > > this case is necessary and someone might "optimitise" it away later. It > > would be preferable if it was self-documenting. Maybe something like > > this? (This is totally untested) > > This issue is not limited to suspend, any GFP_NOIO allocation could > end up in the same loop. Suspend is the most likely case, because it > effectively converts all GFP_KERNEL allocations into GFP_NOIO. > I see what you mean with GFP_NOIO but there is an important difference between GFP_NOIO and suspend. A GFP_NOIO low-order allocation currently implies __GFP_NOFAIL as commented on in should_alloc_retry(). If no progress is made, we call wait_iff_congested() and sleep for a bit. As the system is running, kswapd and other process activity will proceed and eventually reclaim enough pages for the GFP_NOIO allocation to succeed. In a running system, GFP_NOIO can stall for a period of time but your patch will cause the allocation to fail. While I expect callers return ENOMEM or handle the situation properly with a wait-and-retry loop, there will be operations that fail that used to succeed. This is why I'd prefer it was a suspend-specific fix unless we know there is a case where a machine livelocks due to a GFP_NOIO allocation looping forever and even then I'd wonder why kswapd was not helping. -- Mel Gorman SUSE Labs -- 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>