On Tue, Sep 25, 2018 at 02:03:25PM +0200, Michal Hocko wrote:
From: Andrea Arcangeli aarcange@redhat.com
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@redhat.com
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.