kernel.git/mm/mempolicy.c, branch linux-4.18.y

mm: thp: relax __GFP_THISNODE for MADV_HUGEPAGE mappings

2018-11-21T08:22:05Z

commit ac5b2c18911ffe95c08d69273917f90212cf5659 upstream. 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 0000001 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 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 similar, 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 Mel said: : Both patches look correct to me but I'm responding to this one because : it's the fix. The change makes sense and moves further away from the : severe stalling behaviour we used to see with both THP and zone reclaim : mode. : : I put together a basic experiment with usemem configured to reference a : buffer multiple times that is 80% the size of main memory on a 2-socket : box with symmetric node sizes and defrag set to "always". The defrag : setting is not the default but it would be functionally similar to : accessing a buffer with madvise(MADV_HUGEPAGE). Usemem is configured to : reference the buffer multiple times and while it's not an interesting : workload, it would be expected to complete reasonably quickly as it fits : within memory. The results were; : : usemem : vanilla noreclaim-v1 : Amean Elapsd-1 42.78 ( 0.00%) 26.87 ( 37.18%) : Amean Elapsd-3 27.55 ( 0.00%) 7.44 ( 73.00%) : Amean Elapsd-4 5.72 ( 0.00%) 5.69 ( 0.45%) : : This shows the elapsed time in seconds for 1 thread, 3 threads and 4 : threads referencing buffers 80% the size of memory. With the patches : applied, it's 37.18% faster for the single thread and 73% faster with two : threads. Note that 4 threads showing little difference does not indicate : the problem is related to thread counts. It's simply the case that 4 : threads gets spread so their workload mostly fits in one node. : : The overall view from /proc/vmstats is more startling : : 4.19.0-rc1 4.19.0-rc1 : vanillanoreclaim-v1r1 : Minor Faults 35593425 708164 : Major Faults 484088 36 : Swap Ins 3772837 0 : Swap Outs 3932295 0 : : Massive amounts of swap in/out without the patch : : Direct pages scanned 6013214 0 : Kswapd pages scanned 0 0 : Kswapd pages reclaimed 0 0 : Direct pages reclaimed 4033009 0 : : Lots of reclaim activity without the patch : : Kswapd efficiency 100% 100% : Kswapd velocity 0.000 0.000 : Direct efficiency 67% 100% : Direct velocity 11191.956 0.000 : : Mostly from direct reclaim context as you'd expect without the patch. : : Page writes by reclaim 3932314.000 0.000 : Page writes file 19 0 : Page writes anon 3932295 0 : Page reclaim immediate 42336 0 : : Writes from reclaim context is never good but the patch eliminates it. : : We should never have default behaviour to thrash the system for such a : basic workload. If zone reclaim mode behaviour is ever desired but on a : single task instead of a global basis then the sensible option is to build : a mempolicy that enforces that behaviour. This was a severe regression compared to previous kernels that made important workloads unusable and it starts when __GFP_THISNODE was added to THP allocations under MADV_HUGEPAGE. It is not a significant risk to go to the previous behavior before __GFP_THISNODE was added, it worked like that for years. This was simply an optimization to some lucky workloads that can fit in a single node, but it ended up breaking the VM for others that can't possibly fit in a single node, so going back is safe. [mhocko@suse.com: rewrote the changelog based on the one from Andrea] Link: http://lkml.kernel.org/r/20180925120326.24392-2-mhocko@kernel.org Fixes: 5265047ac301 ("mm, thp: really limit transparent hugepage allocation to local node") Signed-off-by: Andrea Arcangeli Signed-off-by: Michal Hocko Reported-by: Stefan Priebe Debugged-by: Andrea Arcangeli Reported-by: Alex Williamson Reviewed-by: Mel Gorman Tested-by: Mel Gorman Cc: Zi Yan Cc: Vlastimil Babka Cc: David Rientjes Cc: "Kirill A. Shutemov" Cc: [4.1+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

mm: use vma_init() to initialize VMAs on stack and data segments

2018-07-27T02:38:03Z

Make sure to initialize all VMAs properly, not only those which come from vm_area_cachep. Link: http://lkml.kernel.org/r/20180724121139.62570-3-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov Acked-by: Linus Torvalds Reviewed-by: Andrew Morton Cc: Dmitry Vyukov Cc: Oleg Nesterov Cc: Andrea Arcangeli Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: unclutter THP migration

2018-04-11T17:28:32Z

THP migration is hacked into the generic migration with rather surprising semantic. The migration allocation callback is supposed to check whether the THP can be migrated at once and if that is not the case then it allocates a simple page to migrate. unmap_and_move then fixes that up by spliting the THP into small pages while moving the head page to the newly allocated order-0 page. Remaning pages are moved to the LRU list by split_huge_page. The same happens if the THP allocation fails. This is really ugly and error prone [1]. I also believe that split_huge_page to the LRU lists is inherently wrong because all tail pages are not migrated. Some callers will just work around that by retrying (e.g. memory hotplug). There are other pfn walkers which are simply broken though. e.g. madvise_inject_error will migrate head and then advances next pfn by the huge page size. do_move_page_to_node_array, queue_pages_range (migrate_pages, mbind), will simply split the THP before migration if the THP migration is not supported then falls back to single page migration but it doesn't handle tail pages if the THP migration path is not able to allocate a fresh THP so we end up with ENOMEM and fail the whole migration which is a questionable behavior. Page compaction doesn't try to migrate large pages so it should be immune. This patch tries to unclutter the situation by moving the special THP handling up to the migrate_pages layer where it actually belongs. We simply split the THP page into the existing list if unmap_and_move fails with ENOMEM and retry. So we will _always_ migrate all THP subpages and specific migrate_pages users do not have to deal with this case in a special way. [1] http://lkml.kernel.org/r/20171121021855.50525-1-zi.yan@sent.com Link: http://lkml.kernel.org/r/20180103082555.14592-4-mhocko@kernel.org Signed-off-by: Michal Hocko Acked-by: Kirill A. Shutemov Reviewed-by: Zi Yan Cc: Andrea Reale Cc: Anshuman Khandual Cc: Mike Kravetz Cc: Naoya Horiguchi Cc: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, migrate: remove reason argument from new_page_t

2018-04-11T17:28:32Z

No allocation callback is using this argument anymore. new_page_node used to use this parameter to convey node_id resp. migration error up to move_pages code (do_move_page_to_node_array). The error status never made it into the final status field and we have a better way to communicate node id to the status field now. All other allocation callbacks simply ignored the argument so we can drop it finally. [mhocko@suse.com: fix migration callback] Link: http://lkml.kernel.org/r/20180105085259.GH2801@dhcp22.suse.cz [akpm@linux-foundation.org: fix alloc_misplaced_dst_page()] [mhocko@kernel.org: fix build] Link: http://lkml.kernel.org/r/20180103091134.GB11319@dhcp22.suse.cz Link: http://lkml.kernel.org/r/20180103082555.14592-3-mhocko@kernel.org Signed-off-by: Michal Hocko Reviewed-by: Zi Yan Cc: Andrea Reale Cc: Anshuman Khandual Cc: Kirill A. Shutemov Cc: Mike Kravetz Cc: Naoya Horiguchi Cc: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, numa: rework do_pages_move

2018-04-11T17:28:32Z

Patch series "unclutter thp migration" Motivation: THP migration is hacked into the generic migration with rather surprising semantic. The migration allocation callback is supposed to check whether the THP can be migrated at once and if that is not the case then it allocates a simple page to migrate. unmap_and_move then fixes that up by splitting the THP into small pages while moving the head page to the newly allocated order-0 page. Remaining pages are moved to the LRU list by split_huge_page. The same happens if the THP allocation fails. This is really ugly and error prone [2]. I also believe that split_huge_page to the LRU lists is inherently wrong because all tail pages are not migrated. Some callers will just work around that by retrying (e.g. memory hotplug). There are other pfn walkers which are simply broken though. e.g. madvise_inject_error will migrate head and then advances next pfn by the huge page size. do_move_page_to_node_array, queue_pages_range (migrate_pages, mbind), will simply split the THP before migration if the THP migration is not supported then falls back to single page migration but it doesn't handle tail pages if the THP migration path is not able to allocate a fresh THP so we end up with ENOMEM and fail the whole migration which is a questionable behavior. Page compaction doesn't try to migrate large pages so it should be immune. The first patch reworks do_pages_move which relies on a very ugly calling semantic when the return status is pushed to the migration path via private pointer. It uses pre allocated fixed size batching to achieve that. We simply cannot do the same if a THP is to be split during the migration path which is done in the patch 3. Patch 2 is follow up cleanup which removes the mentioned return status calling convention ugliness. On a side note: There are some semantic issues I have encountered on the way when working on patch 1 but I am not addressing them here. E.g. trying to move THP tail pages will result in either success or EBUSY (the later one more likely once we isolate head from the LRU list). Hugetlb reports EACCESS on tail pages. Some errors are reported via status parameter but migration failures are not even though the original `reason' argument suggests there was an intention to do so. From a quick look into git history this never worked. I have tried to keep the semantic unchanged. Then there is a relatively minor thing that the page isolation might fail because of pages not being on the LRU - e.g. because they are sitting on the per-cpu LRU caches. Easily fixable. This patch (of 3): do_pages_move is supposed to move user defined memory (an array of addresses) to the user defined numa nodes (an array of nodes one for each address). The user provided status array then contains resulting numa node for each address or an error. The semantic of this function is little bit confusing because only some errors are reported back. Notably migrate_pages error is only reported via the return value. This patch doesn't try to address these semantic nuances but rather change the underlying implementation. Currently we are processing user input (which can be really large) in batches which are stored to a temporarily allocated page. Each address is resolved to its struct page and stored to page_to_node structure along with the requested target numa node. The array of these structures is then conveyed down the page migration path via private argument. new_page_node then finds the corresponding structure and allocates the proper target page. What is the problem with the current implementation and why to change it? Apart from being quite ugly it also doesn't cope with unexpected pages showing up on the migration list inside migrate_pages path. That doesn't happen currently but the follow up patch would like to make the thp migration code more clear and that would need to split a THP into the list for some cases. How does the new implementation work? Well, instead of batching into a fixed size array we simply batch all pages that should be migrated to the same node and isolate all of them into a linked list which doesn't require any additional storage. This should work reasonably well because page migration usually migrates larger ranges of memory to a specific node. So the common case should work equally well as the current implementation. Even if somebody constructs an input where the target numa nodes would be interleaved we shouldn't see a large performance impact because page migration alone doesn't really benefit from batching. mmap_sem batching for the lookup is quite questionable and isolate_lru_page which would benefit from batching is not using it even in the current implementation. Link: http://lkml.kernel.org/r/20180103082555.14592-2-mhocko@kernel.org Signed-off-by: Michal Hocko Acked-by: Kirill A. Shutemov Reviewed-by: Andrew Morton Cc: Anshuman Khandual Cc: Zi Yan Cc: Naoya Horiguchi Cc: Vlastimil Babka Cc: Andrea Reale Cc: Kirill A. Shutemov Cc: Mike Kravetz Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge branch 'syscalls-next' of git://git.kernel.org/pub/scm/linux/kernel/git/brodo/linux

2018-04-03T04:22:12Z

Pull removal of in-kernel calls to syscalls from Dominik Brodowski: "System calls are interaction points between userspace and the kernel. Therefore, system call functions such as sys_xyzzy() or compat_sys_xyzzy() should only be called from userspace via the syscall table, but not from elsewhere in the kernel. At least on 64-bit x86, it will likely be a hard requirement from v4.17 onwards to not call system call functions in the kernel: It is better to use use a different calling convention for system calls there, where struct pt_regs is decoded on-the-fly in a syscall wrapper which then hands processing over to the actual syscall function. This means that only those parameters which are actually needed for a specific syscall are passed on during syscall entry, instead of filling in six CPU registers with random user space content all the time (which may cause serious trouble down the call chain). Those x86-specific patches will be pushed through the x86 tree in the near future. Moreover, rules on how data may be accessed may differ between kernel data and user data. This is another reason why calling sys_xyzzy() is generally a bad idea, and -- at most -- acceptable in arch-specific code. This patchset removes all in-kernel calls to syscall functions in the kernel with the exception of arch/. On top of this, it cleans up the three places where many syscalls are referenced or prototyped, namely kernel/sys_ni.c, include/linux/syscalls.h and include/linux/compat.h" * 'syscalls-next' of git://git.kernel.org/pub/scm/linux/kernel/git/brodo/linux: (109 commits) bpf: whitelist all syscalls for error injection kernel/sys_ni: remove {sys_,sys_compat} from cond_syscall definitions kernel/sys_ni: sort cond_syscall() entries syscalls/x86: auto-create compat_sys_*() prototypes syscalls: sort syscall prototypes in include/linux/compat.h net: remove compat_sys_*() prototypes from net/compat.h syscalls: sort syscall prototypes in include/linux/syscalls.h kexec: move sys_kexec_load() prototype to syscalls.h x86/sigreturn: use SYSCALL_DEFINE0 x86: fix sys_sigreturn() return type to be long, not unsigned long x86/ioport: add ksys_ioperm() helper; remove in-kernel calls to sys_ioperm() mm: add ksys_readahead() helper; remove in-kernel calls to sys_readahead() mm: add ksys_mmap_pgoff() helper; remove in-kernel calls to sys_mmap_pgoff() mm: add ksys_fadvise64_64() helper; remove in-kernel call to sys_fadvise64_64() fs: add ksys_fallocate() wrapper; remove in-kernel calls to sys_fallocate() fs: add ksys_p{read,write}64() helpers; remove in-kernel calls to syscalls fs: add ksys_truncate() wrapper; remove in-kernel calls to sys_truncate() fs: add ksys_sync_file_range helper(); remove in-kernel calls to syscall kernel: add ksys_setsid() helper; remove in-kernel call to sys_setsid() kernel: add ksys_unshare() helper; remove in-kernel calls to sys_unshare() ...

mm: add kernel_[sg]et_mempolicy() helpers; remove in-kernel calls to syscalls

2018-04-02T18:15:34Z

Using the mm-internal kernel_[sg]et_mempolicy() helper allows us to get rid of the mm-internal calls to the sys_[sg]et_mempolicy() syscalls. This patch is part of a series which removes in-kernel calls to syscalls. On this basis, the syscall entry path can be streamlined. For details, see http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net Cc: Al Viro Cc: linux-mm@kvack.org Cc: Andrew Morton Signed-off-by: Dominik Brodowski

mm: add kernel_mbind() helper; remove in-kernel call to syscall

2018-04-02T18:15:33Z

Using the mm-internal kernel_mbind() helper allows us to get rid of the mm-internal call to the sys_mbind() syscall. This patch is part of a series which removes in-kernel calls to syscalls. On this basis, the syscall entry path can be streamlined. For details, see http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net Cc: Al Viro Cc: linux-mm@kvack.org Cc: Andrew Morton Signed-off-by: Dominik Brodowski

mm: add kernel_migrate_pages() helper, move compat syscall to mm/mempolicy.c

2018-04-02T18:15:31Z

Move compat_sys_migrate_pages() to mm/mempolicy.c and make it call a newly introduced helper -- kernel_migrate_pages() -- instead of the syscall. This patch is part of a series which removes in-kernel calls to syscalls. On this basis, the syscall entry path can be streamlined. For details, see http://lkml.kernel.org/r/20180325162527.GA17492@light.dominikbrodowski.net Cc: Al Viro Cc: linux-mm@kvack.org Cc: Andrew Morton Signed-off-by: Dominik Brodowski

mm/mempolicy.c: avoid use uninitialized preferred_node

2018-03-23T00:07:01Z

Alexander reported a use of uninitialized memory in __mpol_equal(), which is caused by incorrect use of preferred_node. When mempolicy in mode MPOL_PREFERRED with flags MPOL_F_LOCAL, it uses numa_node_id() instead of preferred_node, however, __mpol_equal() uses preferred_node without checking whether it is MPOL_F_LOCAL or not. [akpm@linux-foundation.org: slight comment tweak] Link: http://lkml.kernel.org/r/4ebee1c2-57f6-bcb8-0e2d-1833d1ee0bb7@huawei.com Fixes: fc36b8d3d819 ("mempolicy: use MPOL_F_LOCAL to Indicate Preferred Local Policy") Signed-off-by: Yisheng Xie Reported-by: Alexander Potapenko Tested-by: Alexander Potapenko Reviewed-by: Andrew Morton Cc: Dmitriy Vyukov Cc: Vlastimil Babka Cc: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds