On Tue, Sep 25, 2018 at 02:03:25PM +0200, Michal Hocko wrote: > From: Andrea Arcangeli <aarcange@xxxxxxxxxx> > > THP allocation might be really disruptive when allocated on NUMA system > with the local node full or hard to reclaim. Stefan has posted an > allocation stall report on 4.12 based SLES kernel which suggests the > same issue: > > [245513.362669] kvm: page allocation stalls for 194572ms, order:9, mode:0x4740ca(__GFP_HIGHMEM|__GFP_IO|__GFP_FS|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL|__GFP_THISNODE|__GFP_MOVABLE|__GFP_DIRECT_RECLAIM), nodemask=(null) > [245513.363983] kvm cpuset=/ mems_allowed=0-1 > [245513.364604] CPU: 10 PID: 84752 Comm: kvm Tainted: G W 4.12.0+98-ph <a href="/view.php?id=1" title="[geschlossen] Integration Ramdisk" class="resolved">0000001</a> SLE15 (unreleased) > [245513.365258] Hardware name: Supermicro SYS-1029P-WTRT/X11DDW-NT, BIOS 2.0 12/05/2017 > [245513.365905] Call Trace: > [245513.366535] dump_stack+0x5c/0x84 > [245513.367148] warn_alloc+0xe0/0x180 > [245513.367769] __alloc_pages_slowpath+0x820/0xc90 > [245513.368406] ? __slab_free+0xa9/0x2f0 > [245513.369048] ? __slab_free+0xa9/0x2f0 > [245513.369671] __alloc_pages_nodemask+0x1cc/0x210 > [245513.370300] alloc_pages_vma+0x1e5/0x280 > [245513.370921] do_huge_pmd_wp_page+0x83f/0xf00 > [245513.371554] ? set_huge_zero_page.isra.52.part.53+0x9b/0xb0 > [245513.372184] ? do_huge_pmd_anonymous_page+0x631/0x6d0 > [245513.372812] __handle_mm_fault+0x93d/0x1060 > [245513.373439] handle_mm_fault+0xc6/0x1b0 > [245513.374042] __do_page_fault+0x230/0x430 > [245513.374679] ? get_vtime_delta+0x13/0xb0 > [245513.375411] do_page_fault+0x2a/0x70 > [245513.376145] ? page_fault+0x65/0x80 > [245513.376882] page_fault+0x7b/0x80 > [...] > [245513.382056] Mem-Info: > [245513.382634] active_anon:126315487 inactive_anon:1612476 isolated_anon:5 > active_file:60183 inactive_file:245285 isolated_file:0 > unevictable:15657 dirty:286 writeback:1 unstable:0 > slab_reclaimable:75543 slab_unreclaimable:2509111 > mapped:81814 shmem:31764 pagetables:370616 bounce:0 > free:32294031 free_pcp:6233 free_cma:0 > [245513.386615] Node 0 active_anon:254680388kB inactive_anon:1112760kB active_file:240648kB inactive_file:981168kB unevictable:13368kB isolated(anon):0kB isolated(file):0kB mapped:280240kB dirty:1144kB writeback:0kB shmem:95832kB shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 81225728kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no > [245513.388650] Node 1 active_anon:250583072kB inactive_anon:5337144kB active_file:84kB inactive_file:0kB unevictable:49260kB isolated(anon):20kB isolated(file):0kB mapped:47016kB dirty:0kB writeback:4kB shmem:31224kB shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 31897600kB writeback_tmp:0kB unstable:0kB all_unreclaimable? no > > The defrag mode is "madvise" and from the above report it is clear that > the THP has been allocated for MADV_HUGEPAGA vma. > > Andrea has identified that the main source of the problem is > __GFP_THISNODE usage: > > : The problem is that direct compaction combined with the NUMA > : __GFP_THISNODE logic in mempolicy.c is telling reclaim to swap very > : hard the local node, instead of failing the allocation if there's no > : THP available in the local node. > : > : Such logic was ok until __GFP_THISNODE was added to the THP allocation > : path even with MPOL_DEFAULT. > : > : The idea behind the __GFP_THISNODE addition, is that it is better to > : provide local memory in PAGE_SIZE units than to use remote NUMA THP > : backed memory. That largely depends on the remote latency though, on > : threadrippers for example the overhead is relatively low in my > : experience. > : > : The combination of __GFP_THISNODE and __GFP_DIRECT_RECLAIM results in > : extremely slow qemu startup with vfio, if the VM is larger than the > : size of one host NUMA node. This is because it will try very hard to > : unsuccessfully swapout get_user_pages pinned pages as result of the > : __GFP_THISNODE being set, instead of falling back to PAGE_SIZE > : allocations and instead of trying to allocate THP on other nodes (it > : would be even worse without vfio type1 GUP pins of course, except it'd > : be swapping heavily instead). > > Fix this by removing __GFP_THISNODE for THP requests which are > requesting the direct reclaim. This effectivelly reverts 5265047ac301 on > the grounds that the zone/node reclaim was known to be disruptive due > to premature reclaim when there was memory free. While it made sense at > the time for HPC workloads without NUMA awareness on rare machines, it > was ultimately harmful in the majority of cases. The existing behaviour > is similiar, if not as widespare as it applies to a corner case but > crucially, it cannot be tuned around like zone_reclaim_mode can. The > default behaviour should always be to cause the least harm for the > common case. > > If there are specialised use cases out there that want zone_reclaim_mode > in specific cases, then it can be built on top. Longterm we should > consider a memory policy which allows for the node reclaim like behavior > for the specific memory ranges which would allow a > > [1] http://lkml.kernel.org/r/20180820032204.9591-1-aarcange@xxxxxxxxxx > I think we have a similar problem elsewhere too I've run into cases where alloc_pool_huge_page() took forever looping in reclaim via compaction_test. My tests and tracing eventually showed that the root cause was we were looping in should_continue_reclaim() due to __GFP_RETRY_MAYFAIL (set in alloc_fresh_huge_page()). The scanned value was much lesser than sc->order. I have a small RFC patch that I am testing and it seems good to so far, having said that the issue is hard to reproduce and takes a while to hit. I wonder if alloc_pool_huge_page() should also trim out it's logic of __GFP_THISNODE for the same reasons as mentioned here. I like that we round robin to alloc the pool pages, but __GFP_THISNODE might be an overkill for that case as well. Balbir Singh.
