On Tue, Oct 25, 2011 at 4:23 AM, Mel Gorman <mgorman@xxxxxxx> wrote: > 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. OK, I see the change in behavior you are trying to avoid. With your patch GFP_NOIO allocations can still fail during suspend, is that OK? I'm also worried about GFP_NOIO allocations looping forever when swap is not enabled, but I've never seen it happen, and it would probably recover eventually when another tried tried a GFP_KERNEL allocation and oom killed something. -- 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