Messages in this thread | | | Subject | Re: [PATCH V4] mlx4_core: allocate ICM memory in page size chunks | From | Qing Huang <> | Date | Tue, 5 Jun 2018 11:51:18 -0700 |
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On 6/4/2018 5:40 AM, Vlastimil Babka wrote: > On 06/04/2018 08:27 AM, Michal Hocko wrote: >> On Fri 01-06-18 15:05:26, Qing Huang wrote: >>> >>> On 6/1/2018 12:31 AM, Michal Hocko wrote: >>>> On Thu 31-05-18 19:04:46, Qing Huang wrote: >>>>> On 5/31/2018 2:10 AM, Michal Hocko wrote: >>>>>> On Thu 31-05-18 10:55:32, Michal Hocko wrote: >>>>>>> On Thu 31-05-18 04:35:31, Eric Dumazet wrote: >>>>>> [...] >>>>>>>> I merely copied/pasted from alloc_skb_with_frags() :/ >>>>>>> I will have a look at it. Thanks! >>>>>> OK, so this is an example of an incremental development ;). >>>>>> >>>>>> __GFP_NORETRY was added by ed98df3361f0 ("net: use __GFP_NORETRY for >>>>>> high order allocations") to prevent from OOM killer. Yet this was >>>>>> not enough because fb05e7a89f50 ("net: don't wait for order-3 page >>>>>> allocation") didn't want an excessive reclaim for non-costly orders >>>>>> so it made it completely NOWAIT while it preserved __GFP_NORETRY in >>>>>> place which is now redundant. Should I send a patch? >>>>>> >>>>> Just curious, how about GFP_ATOMIC flag? Would it work in a similar fashion? >>>>> We experimented >>>>> with it a bit in the past but it seemed to cause other issue in our tests. >>>>> :-) >>>> GFP_ATOMIC is a non-sleeping (aka no reclaim) context with an access to >>>> memory reserves. So the risk is that you deplete those reserves and >>>> cause issues to other subsystems which need them as well. >>>> >>>>> By the way, we didn't encounter any OOM killer events. It seemed that the >>>>> mlx4_alloc_icm() triggered slowpath. >>>>> We still had about 2GB free memory while it was highly fragmented. >>>> The compaction was able to make a reasonable forward progress for you. >>>> But considering mlx4_alloc_icm is called with GFP_KERNEL resp. GFP_HIGHUSER >>>> then the OOM killer is clearly possible as long as the order is lower >>>> than 4. >>> The allocation was 256KB so the order was much higher than 4. The compaction >>> seemed to be the root >>> cause for our problem. It took too long to finish its work while putting >>> mlx4_alloc_icm to sleep in a heavily >>> fragmented memory situation . Will NORETRY flag avoid the compaction ops and >>> fail the 256KB allocation >>> immediately so mlx4_alloc_icm can enter adjustable lower order allocation >>> code path quickly? >> Costly orders should only perform a light compaction attempt unless >> __GFP_RETRY_MAY_FAIL is used IIRC. CCing Vlastimil. So __GFP_NORETRY >> shouldn't make any difference. > It's a bit more complicated. Costly allocations will try the light > compaction attempt first, even before reclaim. This is followed by > reclaim and a more costly compaction attempt. With __GFP_NORETRY, the > second compaction attempt is also only the light one, so the flag does > make a difference here.
Thanks for the clarification!
Looks like our production kernel is kinda old, neither __GFP_DIRECT_RECLAIM nor __GFP_NORETRY has been used in __alloc_pages_slowpath() in our kernel.
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