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The source for the Linux kernel used in Windows Subsystem for Linux 2 (WSL2)
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Li Xinhai 8ac0b81ab1 mm/hugetlb: avoid unnecessary check on pud and pmd entry in huge_pte_offset 
When huge_pte_offset() is called, the parameter sz can only be PUD_SIZE or
PMD_SIZE.  If sz is PUD_SIZE and code can reach pud, then *pud must be
none, or normal hugetlb entry, or non-present (migration or hwpoisoned)
hugetlb entry, and we can directly return pud.  When sz is PMD_SIZE, pud
must be none or present, and if code can reach pmd, we can directly return
pmd.

So after this patch the code is simplified by first check on the parameter
sz, and avoid unnecessary checks in current code.  Same semantics of
existing code is maintained.

More details about relevant commits:
commit 9b19df292c ("mm/hugetlb.c: make huge_pte_offset() consistent
and document behaviour") changed the code path for pud and pmd handling,
see comments about why this patch intends to change it.
...
	pud = pud_offset(p4d, addr);
	if (sz != PUD_SIZE && pud_none(*pud)) // [1]
		return NULL;
	/* hugepage or swap? */
	if (pud_huge(*pud) || !pud_present(*pud)) // [2]
		return (pte_t *)pud;

	pmd = pmd_offset(pud, addr);
	if (sz != PMD_SIZE && pmd_none(*pmd)) // [3]
		return NULL;
	/* hugepage or swap? */
	if (pmd_huge(*pmd) || !pmd_present(*pmd)) // [4]
		return (pte_t *)pmd;

	return NULL; // [5]
...
[1]: this is necessary, return NULL for sz == PMD_SIZE;
[2]: if sz == PUD_SIZE, all valid values of pud entry will cause return;
[3]: dead code, sz != PMD_SIZE never true;
[4]: all valid values of pmd entry will cause return;
[5]: dead code, because of check in [4].

Now, this patch combines [1] and [2] for pud, and combines [3], [4] and
[5] for pmd, so avoid unnecessary checks.

I don't try to catch any invalid values in page table entry, as that will
be checked by caller and avoid extra branch in this function.  Also no
assert on sz must equal PUD_SIZE or PMD_SIZE, since this function only
call for hugetlb mapping.

For commit 3c1d7e6ccb ("mm/hugetlb: fix a addressing exception caused by
huge_pte_offset"), since we don't read the entry more than once now,
variable pud_entry and pmd_entry are not needed.

Signed-off-by: Li Xinhai <lixinhai.lxh@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: Punit Agrawal <punit.agrawal@arm.com>
Cc: Longpeng <longpeng2@huawei.com>
Link: http://lkml.kernel.org/r/1587794313-16849-1-git-send-email-lixinhai.lxh@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2020-06-03 20:09:46 -07:00
Documentation hugetlbfs: clean up command line processing 2020-06-03 20:09:46 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch hugetlbfs: remove hugetlb_add_hstate() warning for existing hstate 2020-06-03 20:09:46 -07:00
block for-5.8/drivers-2020-06-01 2020-06-02 15:37:03 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto crypto: engine - do not requeue in case of fatal error 2020-05-28 17:27:52 +10:00
drivers drm/i915: convert get_user_pages() --> pin_user_pages() 2020-06-03 20:09:42 -07:00
fs Changes since last update: 2020-06-02 20:16:55 -07:00
include hugetlbfs: move hugepagesz= parsing to arch independent code 2020-06-03 20:09:46 -07:00
init padata: initialize earlier 2020-06-03 20:09:45 -07:00
ipc ipc/util.c: sysvipc_find_ipc() incorrectly updates position index 2020-05-14 10:00:35 -07:00
kernel padata: add basic support for multithreaded jobs 2020-06-03 20:09:45 -07:00
lib kasan: stop tests being eliminated as dead code with FORTIFY_SOURCE 2020-06-03 20:09:42 -07:00
mm mm/hugetlb: avoid unnecessary check on pud and pmd entry in huge_pte_offset 2020-06-03 20:09:46 -07:00
net audit/stable-5.8 PR 20200601 2020-06-02 17:13:37 -07:00
samples Merge branch 'from-miklos' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-06-01 16:44:06 -07:00
scripts A fair amount of stuff this time around, dominated by yet another massive 2020-06-01 15:45:27 -07:00
security Merge branch 'next-general' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2020-06-02 17:36:24 -07:00
sound Merge branch 'akpm' (patches from Andrew) 2020-06-02 12:21:36 -07:00
tools khugepaged: introduce 'max_ptes_shared' tunable 2020-06-03 20:09:46 -07:00
usr kbuild: fix comment about missing include guard detection 2020-04-11 12:09:48 +09:00
virt A fair amount of stuff this time around, dominated by yet another massive 2020-06-01 15:45:27 -07:00
.clang-format block: add bio_for_each_bvec_all() 2020-05-25 11:25:24 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
.mailmap A fair amount of stuff this time around, dominated by yet another massive 2020-06-01 15:45:27 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS mailmap: change email for Ricardo Ribalda 2020-05-25 18:59:59 -06:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS for-5.8/drivers-2020-06-01 2020-06-02 15:37:03 -07:00
Makefile arm64 updates for 5.8 2020-06-01 15:18:27 -07:00
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.