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b53d209d71
commit 81e506bec9be1eceaf5a2c654e28ba5176ef48d8 upstream. Kernel build regression with LLVM was reported here: https://lore.kernel.org/all/Y1GCYXGtEVZbcv%2F5@dev-arch.thelio-3990X/ with commit f35b5d7d676e ("mm: align larger anonymous mappings on THP boundaries"). And the commit f35b5d7d676e was reverted. It turned out the regression is related with madvise(MADV_DONTNEED) was used by ld.lld. But with none PMD_SIZE aligned parameter len. trace-bpfcc captured: 531607 531732 ld.lld do_madvise.part.0 start: 0x7feca9000000, len: 0x7fb000, behavior: 0x4 531607 531793 ld.lld do_madvise.part.0 start: 0x7fec86a00000, len: 0x7fb000, behavior: 0x4 If the underneath physical page is THP, the madvise(MADV_DONTNEED) can trigger split_queue_lock contention raised significantly. perf showed following data: 14.85% 0.00% ld.lld [kernel.kallsyms] [k] entry_SYSCALL_64_after_hwframe 11.52% entry_SYSCALL_64_after_hwframe do_syscall_64 __x64_sys_madvise do_madvise.part.0 zap_page_range unmap_single_vma unmap_page_range page_remove_rmap deferred_split_huge_page __lock_text_start native_queued_spin_lock_slowpath If THP can't be removed from rmap as whole THP, partial THP will be removed from rmap by removing sub-pages from rmap. Even the THP head page is added to deferred queue already, the split_queue_lock will be acquired and check whether the THP head page is in the queue already. Thus, the contention of split_queue_lock is raised. Before acquire split_queue_lock, check and bail out early if the THP head page is in the queue already. The checking without holding split_queue_lock could race with deferred_split_scan, but it doesn't impact the correctness here. Test result of building kernel with ld.lld: commit 7b5a0b664ebe (parent commit of f35b5d7d676e): time -f "\t%E real,\t%U user,\t%S sys" make LD=ld.lld -skj96 allmodconfig all 6:07.99 real, 26367.77 user, 5063.35 sys commit f35b5d7d676e: time -f "\t%E real,\t%U user,\t%S sys" make LD=ld.lld -skj96 allmodconfig all 7:22.15 real, 26235.03 user, 12504.55 sys commit f35b5d7d676e with the fixing patch: time -f "\t%E real,\t%U user,\t%S sys" make LD=ld.lld -skj96 allmodconfig all 6:08.49 real, 26520.15 user, 5047.91 sys Link: https://lkml.kernel.org/r/20221223135207.2275317-1-fengwei.yin@intel.com Signed-off-by: Yin Fengwei <fengwei.yin@intel.com> Tested-by: Nathan Chancellor <nathan@kernel.org> Acked-by: David Rientjes <rientjes@google.com> Reviewed-by: "Huang, Ying" <ying.huang@intel.com> Cc: Feng Tang <feng.tang@intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Rik van Riel <riel@surriel.com> Cc: Xing Zhengjun <zhengjun.xing@linux.intel.com> Cc: Yang Shi <shy828301@gmail.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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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.