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Zhigang Lu acbfb087e3 mm/hugetlb: avoid looping to the same hugepage if !pages and !vmas 
When mmapping an existing hugetlbfs file with MAP_POPULATE, we find it
is very time consuming.  For example, mmapping a 128GB file takes about
50 milliseconds.  Sampling with perfevent shows it spends 99% time in
the same_page loop in follow_hugetlb_page().

samples: 205  of event 'cycles', Event count (approx.): 136686374
-  99.04%  test_mmap_huget  [kernel.kallsyms]  [k] follow_hugetlb_page
        follow_hugetlb_page
        __get_user_pages
        __mlock_vma_pages_range
        __mm_populate
        vm_mmap_pgoff
        sys_mmap_pgoff
        sys_mmap
        system_call_fastpath
        __mmap64

follow_hugetlb_page() is called with pages=NULL and vmas=NULL, so for
each hugepage, we run into the same_page loop for pages_per_huge_page()
times, but doing nothing.  With this change, it takes less then 1
millisecond to mmap a 128GB file in hugetlbfs.

Link: http://lkml.kernel.org/r/1567581712-5992-1-git-send-email-totty.lu@gmail.com
Signed-off-by: Zhigang Lu <tonnylu@tencent.com>
Reviewed-by: Haozhong Zhang <hzhongzhang@tencent.com>
Reviewed-by: Zongming Zhang <knightzhang@tencent.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Acked-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2019-12-01 12:59:08 -08:00
Documentation kasan: support backing vmalloc space with real shadow memory 2019-12-01 12:59:05 -08:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch powerpc/mm: remove pmd_huge/pud_huge stubs and include hugetlb.h 2019-12-01 12:59:08 -08:00
block for-5.5/disk-revalidate-20191122 2019-11-25 11:37:01 -08:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto Merge git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2019-11-25 19:49:58 -08:00
drivers drivers/base/memory.c: drop the mem_sysfs_mutex 2019-12-01 12:59:04 -08:00
fs hugetlb: remove unused hstate in hugetlb_fault_mutex_hash() 2019-12-01 12:59:08 -08:00
include hugetlb: remove unused hstate in hugetlb_fault_mutex_hash() 2019-12-01 12:59:08 -08:00
init Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2019-11-25 20:02:57 -08:00
ipc ipc/sem.c: convert to use built-in RCU list checking 2019-09-25 17:51:41 -07:00
kernel kernel: sysctl: make drop_caches write-only 2019-12-01 12:59:07 -08:00
lib kasan: add test for vmalloc 2019-12-01 12:59:05 -08:00
mm mm/hugetlb: avoid looping to the same hugepage if !pages and !vmas 2019-12-01 12:59:08 -08:00
net for-5.5/io_uring-post-20191128 2019-11-28 10:43:39 -08:00
samples New tracing features: 2019-11-27 11:42:01 -08:00
scripts scripts/spelling.txt: add more spellings to spelling.txt 2019-12-01 06:29:17 -08:00
security drm main pull for 5.5-rc1 2019-11-27 17:45:48 -08:00
sound sound updates for 5.5-rc1 2019-11-26 20:04:35 -08:00
tools selftests: vm: add fragment CONFIG_TEST_VMALLOC 2019-12-01 12:59:05 -08:00
usr kbuild: update compile-test header list for v5.4-rc2 2019-10-05 15:29:49 +09:00
virt KVM: Fix jump label out_free_* in kvm_init() 2019-11-23 11:29:17 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig
…
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap Merge branch 'efi-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-11-26 14:52:11 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS \n 2019-11-30 11:34:33 -08:00
Makefile Linux 5.4 2019-11-24 16:32:01 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

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.