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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: 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) kvm cpuset=/ mems_allowed=0-1 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) Hardware name: Supermicro SYS-1029P-WTRT/X11DDW-NT, BIOS 2.0 12/05/2017 Call Trace: dump_stack+0x5c/0x84 warn_alloc+0xe0/0x180 __alloc_pages_slowpath+0x820/0xc90 __alloc_pages_nodemask+0x1cc/0x210 alloc_pages_vma+0x1e5/0x280 do_huge_pmd_wp_page+0x83f/0xf00 __handle_mm_fault+0x93d/0x1060 handle_mm_fault+0xc6/0x1b0 __do_page_fault+0x230/0x430 do_page_fault+0x2a/0x70 page_fault+0x7b/0x80 [...] Mem-Info: 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 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 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 |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.