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From: Andrew Morton <akpm@linux-foundation.org>
To: jgg@mellanox.com, lixinhai.lxh@gmail.com, longpeng2@huawei.com,
	mike.kravetz@oracle.com, mm-commits@vger.kernel.org,
	punit.agrawal@arm.com
Subject: + mm-hugetlb-avoid-unnecessary-check-on-pud-and-pmd-entry-in-huge_pte_offset.patch added to -mm tree
Date: Sat, 25 Apr 2020 17:17:16 -0700
Message-ID: <20200426001716.a26rjl7W7%akpm@linux-foundation.org> (raw)
In-Reply-To: <20200420181310.c18b3c0aa4dc5b3e5ec1be10@linux-foundation.org>


The patch titled
     Subject: mm/hugetlb: avoid unnecessary check on pud and pmd entry in huge_pte_offset
has been added to the -mm tree.  Its filename is
     mm-hugetlb-avoid-unnecessary-check-on-pud-and-pmd-entry-in-huge_pte_offset.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mm-hugetlb-avoid-unnecessary-check-on-pud-and-pmd-entry-in-huge_pte_offset.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mm-hugetlb-avoid-unnecessary-check-on-pud-and-pmd-entry-in-huge_pte_offset.patch

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------------------------------------------------------
From: Li Xinhai <lixinhai.lxh@gmail.com>
Subject: 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 9b19df292c66 ("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 3c1d7e6ccb64 ("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.

Link: http://lkml.kernel.org/r/1587794313-16849-1-git-send-email-lixinhai.lxh@gmail.com
Signed-off-by: Li Xinhai <lixinhai.lxh@gmail.com>
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hugetlb.c |   28 +++++++++++-----------------
 1 file changed, 11 insertions(+), 17 deletions(-)

--- a/mm/hugetlb.c~mm-hugetlb-avoid-unnecessary-check-on-pud-and-pmd-entry-in-huge_pte_offset
+++ a/mm/hugetlb.c
@@ -5481,8 +5481,8 @@ pte_t *huge_pte_alloc(struct mm_struct *
  * huge_pte_offset() - Walk the page table to resolve the hugepage
  * entry at address @addr
  *
- * Return: Pointer to page table or swap entry (PUD or PMD) for
- * address @addr, or NULL if a p*d_none() entry is encountered and the
+ * Return: Pointer to page table entry (PUD or PMD) for
+ * address @addr, or NULL if a !p*d_present() entry is encountered and the
  * size @sz doesn't match the hugepage size at this level of the page
  * table.
  */
@@ -5491,8 +5491,8 @@ pte_t *huge_pte_offset(struct mm_struct
 {
 	pgd_t *pgd;
 	p4d_t *p4d;
-	pud_t *pud, pud_entry;
-	pmd_t *pmd, pmd_entry;
+	pud_t *pud;
+	pmd_t *pmd;
 
 	pgd = pgd_offset(mm, addr);
 	if (!pgd_present(*pgd))
@@ -5502,22 +5502,16 @@ pte_t *huge_pte_offset(struct mm_struct
 		return NULL;
 
 	pud = pud_offset(p4d, addr);
-	pud_entry = READ_ONCE(*pud);
-	if (sz != PUD_SIZE && pud_none(pud_entry))
-		return NULL;
-	/* hugepage or swap? */
-	if (pud_huge(pud_entry) || !pud_present(pud_entry))
+	if (sz == PUD_SIZE)
+		/* must be pud huge, non-present or none */
 		return (pte_t *)pud;

  parent reply index

Thread overview: 71+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-21  1:13 incoming Andrew Morton
2020-04-21  1:13 ` [patch 01/15] sh: fix build error in mm/init.c Andrew Morton
2020-04-21  1:13 ` [patch 02/15] slub: avoid redzone when choosing freepointer location Andrew Morton
2020-04-21  1:13 ` [patch 03/15] mm/userfaultfd: disable userfaultfd-wp on x86_32 Andrew Morton
2020-04-21  1:13 ` [patch 04/15] MAINTAINERS: add an entry for kfifo Andrew Morton
2020-04-21  1:13 ` [patch 05/15] mm/hugetlb: fix a addressing exception caused by huge_pte_offset Andrew Morton
2020-04-21  1:13 ` [patch 06/15] mm, gup: return EINTR when gup is interrupted by fatal signals Andrew Morton
2020-04-21  1:13 ` [patch 07/15] checkpatch: fix a typo in the regex for $allocFunctions Andrew Morton
2020-04-21  1:14 ` [patch 08/15] tools/build: tweak unused value workaround Andrew Morton
2020-04-21  1:14 ` [patch 09/15] mm/ksm: fix NULL pointer dereference when KSM zero page is enabled Andrew Morton
2020-04-21  1:14 ` [patch 10/15] mm/shmem: fix build without THP Andrew Morton
2020-04-21  1:14 ` [patch 11/15] vmalloc: fix remap_vmalloc_range() bounds checks Andrew Morton
2020-04-21  1:14 ` [patch 12/15] shmem: fix possible deadlocks on shmlock_user_lock Andrew Morton
2020-04-21  1:14 ` [patch 13/15] mm: shmem: disable interrupt when acquiring info->lock in userfaultfd_copy path Andrew Morton
2020-04-21  1:14 ` [patch 14/15] coredump: fix null pointer dereference on coredump Andrew Morton
2020-04-21  1:14 ` [patch 15/15] tools/vm: fix cross-compile build Andrew Morton
2020-04-21  2:00 ` + mm-memory_hotplug-refrain-from-adding-memory-into-an-impossible-node.patch added to -mm tree Andrew Morton
2020-04-21  2:48 ` + x86-mm-define-mm_p4d_folded.patch " Andrew Morton
2020-04-21  2:52 ` + mm-debug-add-tests-validating-architecture-page-table-helpers-v17.patch " Andrew Morton
2020-04-21  2:59 ` + mm-mmapc-add-more-sanity-checks-to-get_unmapped_area.patch " Andrew Morton
2020-04-21  2:59 ` + mm-mmapc-do-not-allow-mappings-outside-of-allowed-limits.patch " Andrew Morton
2020-04-21  3:07 ` + initrdmem=-option-to-specify-initrd-physical-address-checkpatch-fixes.patch " Andrew Morton
2020-04-21  3:58 ` + initrdmem=-option-to-specify-initrd-physical-address.patch " Andrew Morton
2020-04-21  5:43 ` mmotm 2020-04-20-22-43 uploaded Andrew Morton
2020-04-22  1:36 ` + mm-swapfilec-found_free-could-be-represented-by-tmp-max.patch added to -mm tree Andrew Morton
2020-04-22  1:36 ` + mm-swapfilec-tmp-is-always-smaller-than-max.patch " Andrew Morton
2020-04-22  1:36 ` + mm-swapfilec-omit-a-duplicate-code-by-compare-tmp-and-max-first.patch " Andrew Morton
2020-04-23 22:36 ` + kasan-initialise-array-in-kasan_memcmp-test.patch " Andrew Morton
2020-04-23 22:38 ` + kvm-svm-change-flag-passed-to-gup-fast-in-sev_pin_memory.patch " Andrew Morton
2020-04-23 22:41 ` + mm-pass-task-and-mm-to-do_madvise-fix.patch " Andrew Morton
2020-04-23 22:44 ` + mm-support-vector-address-ranges-for-process_madvise.patch " Andrew Morton
2020-04-23 22:44 ` + mm-support-vector-address-ranges-for-process_madvise-fix.patch " Andrew Morton
2020-04-23 22:48 ` + kasan-stop-tests-being-eliminated-as-dead-code-with-fortify_source.patch " Andrew Morton
2020-04-23 22:48 ` + stringh-fix-incompatibility-between-fortify_source-and-kasan.patch " Andrew Morton
2020-04-23 23:03 ` + powerpc-add-support-for-folded-p4d-page-tables-fix.patch " Andrew Morton
2020-04-23 23:09 ` [folded-merged] memcg-optimize-memorynuma_stat-like-memorystat-fix.patch removed from " Andrew Morton
2020-04-23 23:32 ` + slub-remove-userspace-notifier-for-cache-add-remove.patch added to " Andrew Morton
2020-04-23 23:35 ` + ocfs2-mount-shared-volume-without-ha-stack.patch " Andrew Morton
2020-04-24  0:29 ` + mm-memory_hotplug-handle-memblocks-only-with-config_arch_keep_memblock.patch " Andrew Morton
2020-04-24  1:17 ` + mm-return-true-in-cpupid_pid_unset.patch " Andrew Morton
2020-04-24  1:20 ` + kernel-better-document-the-use_mm-unuse_mm-api-contract-v2-fix.patch " Andrew Morton
2020-04-24  1:40 ` + mm-thp-rename-pmd_mknotpresent-as-pmd_mkinvalid-v2.patch " Andrew Morton
2020-04-24  1:47 ` + ipc-convert-ipcs_idr-to-xarray-update.patch " Andrew Morton
     [not found]   ` <20200605195848.GB5393@lca.pw>
     [not found]     ` <20200605201134.GJ19604@bombadil.infradead.org>
2020-06-05 21:20       ` Andrew Morton
2020-12-30 15:44   ` Manfred Spraul
2020-04-24  2:06 ` + powerpc-spufs-simplify-spufs-core-dumping.patch " Andrew Morton
2020-04-24  2:06 ` + signal-factor-copy_siginfo_to_external32-from-copy_siginfo_to_user32.patch " Andrew Morton
2020-04-24  2:06 ` + binfmt_elf-femove-the-set_fs-in-fill_siginfo_note.patch " Andrew Morton
2020-04-24  2:06 ` + binfmt_elf-remove-the-set_fskernel_ds-in-elf_core_dump.patch " Andrew Morton
2020-04-24  2:06 ` + binfmt_elf_fdpic-remove-the-set_fskernel_ds-in-elf_fdpic_core_dump.patch " Andrew Morton
2020-04-24  2:06 ` + exec-simplify-the-copy_strings_kernel-calling-convention.patch " Andrew Morton
2020-04-24  2:06 ` + exec-open-code-copy_string_kernel.patch " Andrew Morton
2020-04-24  3:24 ` + add-kernel-config-option-for-twisting-kernel-behavior.patch " Andrew Morton
2020-04-24  3:24 ` + twist-allow-disabling-k_spec-function-in-drivers-tty-vt-keyboardc.patch " Andrew Morton
2020-04-24  3:24 ` + twist-add-option-for-selecting-twist-options-for-syzkallers-testing.patch " Andrew Morton
2020-04-24  3:32 ` + eventpoll-fix-missing-wakeup-for-ovflist-in-ep_poll_callback.patch " Andrew Morton
2020-04-24  3:49 ` [obsolete] linux-next-rejects.patch removed from " Andrew Morton
2020-04-24  3:51 ` + mips-mm-add-page-soft-dirty-tracking.patch added to " Andrew Morton
2020-04-24 23:36 ` + mm-memory_hotplug-set-node_start_pfn-of-hotadded-pgdat-to-0.patch " Andrew Morton
2020-04-26  0:09 ` + mm-switch-the-test_vmalloc-module-to-use-__vmalloc_node-fix-fix.patch " Andrew Morton
2020-04-26  0:17 ` Andrew Morton [this message]
2020-04-26  0:29 ` + eventpoll-fix-missing-wakeup-for-ovflist-in-ep_poll_callback-v2.patch " Andrew Morton
2020-04-26  0:41 ` [withdrawn] kasan-initialise-array-in-kasan_memcmp-test.patch removed from " Andrew Morton
2020-04-26  0:41 ` + kasan-stop-tests-being-eliminated-as-dead-code-with-fortify_source-v4.patch added to " Andrew Morton
2020-04-26  0:48 ` + checkpatch-test-git_dir-changes.patch " Andrew Morton
2020-04-26  1:06 ` + mm-add-debug_wx-support.patch " Andrew Morton
2020-04-26  1:06 ` + riscv-support-debug_wx.patch " Andrew Morton
2020-04-26  1:06 ` + riscv-support-debug_wx-fix.patch " Andrew Morton
2020-04-26  1:06 ` + x86-mm-use-arch_has_debug_wx-instead-of-arch-defined.patch " Andrew Morton
2020-04-26  1:06 ` + arm64-mm-use-arch_has_debug_wx-instead-of-arch-defined.patch " Andrew Morton
2020-04-26  1:09 ` [folded-merged] initrdmem=-option-to-specify-initrd-physical-address-checkpatch-fixes.patch removed from " Andrew Morton

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