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 Jj1X7Gbf yjsf/GoFp+djhl/eZsKbsJ0fboLVOPkzlmd6fx2e1Cri6r9IDap52Yzs6aDSXRaieD3SthOpbMoBH/fVS0OMdrXT6ae1NSHfXG688BkxYgBqCEfvf+sL/ciONF02T9Lr/6t405PCutSaiQ6s4W3UJYF1TacjhoKZZuLm0RXKx1FSatibr5I9654OTBYbn8LJ79XNwtjuDouB0jzTLaJ3OeojQ21GzaaLqInqZPmP5GwwObw1RdWLWzUe/vvXwSJgCULJN508thhtn+C1HzIgq2ArwfTbLjEtiCePGToR23IEbPTEfzv24tbgeVlr3eyPy0f1OmEGawz02KfeQ4QsSdFsCAWu2ArCrffvLaXYPevNuoTwINdECiqTJZC89B57VbXooPWncqKR0rFABsgefqR9kq2K10nzAgD2PvOuh3KxtWhh252ePoxcS5LnvYRpdtcAyOutQcjy93FsB4jostvkQags7UmJdRnqa/+dg78clZvE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 04/17/23 10:33, Michal Hocko wrote: > On Fri 14-04-23 17:47:28, David Rientjes wrote: > > On Thu, 13 Apr 2023, Michal Hocko wrote: > > > > > [...] > > > > > > This is a theoretical concern. Freeing a 1G page requires 16M of free > > > > > > memory. A machine might need to be reconfigured from one task to > > > > > > another, and release a large number of 1G pages back to the system if > > > > > > allocating 16M fails, the release won't work. > > > > > > > > > > This is really an important "detail" changelog should mention. While I > > > > > am not really against that change I would much rather see that as a > > > > > result of a real world fix rather than a theoretical concern. Mostly > > > > > because a real life scenario would allow us to test the > > > > > __GFP_RETRY_MAYFAIL effectivness. As that request might fail as well we > > > > > just end up with a theoretical fix for a theoretical problem. Something > > > > > that is easy to introduce but much harder to get rid of should we ever > > > > > need to change __GFP_RETRY_MAYFAIL implementation for example. > > > > > > > > I will add this to changelog in v3. If __GFP_RETRY_MAYFAIL is > > > > ineffective we will receive feedback once someone hits this problem. > > > > > > I do not remember anybody hitting this with the current __GFP_NORETRY. > > > So arguably there is nothing to be fixed ATM. > > > > > > > I think we should still at least clear __GFP_NORETRY in this allocation: > > to be able to free 1GB hugepages back to the system we'd like the page > > allocator to at least exercise its normal order-0 allocation logic rather > > than exempting it from retrying reclaim by opting into __GFP_NORETRY. > > > > I'd agree with the analysis in > > https://lore.kernel.org/linux-mm/YCafit5ruRJ+SL8I@dhcp22.suse.cz/ that > > either a cleared __GFP_NORETRY or a __GFP_RETRY_MAYFAIL makes logical > > sense. > > > > We really *do* want to free these hugepages back to the system and the > > amount of memory freeing will always be more than the allocation for > > struct page. The net result is more free memory. > > > > If the allocation fails, we can't free 1GB back to the system on a > > saturated node if our first reclaim attempt didn't allow these struct > > pages to be allocated. Stranding 1GB in the hugetlb pool that no > > userspace on the system can make use of at the time isn't very useful. > > I do not think there is any dispute in the theoretical concern. The question is > whether this is something that really needs a fix in practice. Have we > ever seen workloads which rely on GB pages to fail freeing them? Since I have never seen a failure allocating vmemmmap, I agree that this is all a theoretical concern. However, to me it seems that replacing __GFP_NORETRY with __GFP_RETRY_MAYFAIL would lessen that theoretical concern just a little. That is simply because an allocation with __GFP_RETRY_MAYFAIL would be a little more likely to succeed. Again, I know this is all theoretical but if switching to __GFP_RETRY_MAYFAIL would prevent one allocation/hugetlb page freeing failure I think it is worth it. Because, as soon as we see one failure we may need to look into addressing this now theoretical concern. -- Mike Kravetz