The patch titled
Subject: mm: sparsemem: use page table lock to protect kernel pmd operations
has been added to the -mm tree. Its filename is
mm-sparsemem-use-page-table-lock-to-protect-kernel-pmd-operations.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-sparsemem-use-page-table-lock-to-protect-kernel-pmd-operations.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-sparsemem-use-page-table-lock-to-protect-kernel-pmd-operations.patch
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------------------------------------------------------
From: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Subject: mm: sparsemem: use page table lock to protect kernel pmd operations
The init_mm.page_table_lock is used to protect kernel page tables, we can
use it to serialize splitting vmemmap PMD mappings instead of mmap write
lock, which can increase the concurrency of vmemmap_remap_free().
Actually, It increase the concurrency between allocations of HugeTLB
pages. But it is not the only benefit. There are a lot of users of mmap
read lock of init_mm. The mmap write lock is holding through
vmemmap_remap_free(), removing mmap write lock usage to make it does not
affect other users of mmap read lock. It is not making anything worse and
always a win to move.
Now the kernel page table walker does not hold the page_table_lock when
walking pmd entries. There may be consistency issue of a pmd entry,
because pmd entry might change from a huge pmd entry to a PTE page table.
There is only one user of kernel page table walker, namely ptdump. The
ptdump already considers the consistency, which use a local variable to
cache the value of pmd entry. But we also need to update ->action to
ACTION_CONTINUE to make sure the walker does not walk every pte entry
again when concurrent thread has split the huge pmd.
Link: https://lkml.kernel.org/r/20211101031651.75851-4-songmuchun@xxxxxxxxxxxxx
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Barry Song <song.bao.hua@xxxxxxxxxxxxx>
Cc: Bodeddula Balasubramaniam <bodeddub@xxxxxxxxxx>
Cc: Chen Huang <chenhuang5@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Fam Zheng <fam.zheng@xxxxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Cc: Xiongchun Duan <duanxiongchun@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/ptdump.c | 16 ++++++++++----
mm/sparse-vmemmap.c | 47 +++++++++++++++++++++++++++---------------
2 files changed, 43 insertions(+), 20 deletions(-)
--- a/mm/ptdump.c~mm-sparsemem-use-page-table-lock-to-protect-kernel-pmd-operations
+++ a/mm/ptdump.c
@@ -40,8 +40,10 @@ static int ptdump_pgd_entry(pgd_t *pgd,
if (st->effective_prot)
st->effective_prot(st, 0, pgd_val(val));
- if (pgd_leaf(val))
+ if (pgd_leaf(val)) {
st->note_page(st, addr, 0, pgd_val(val));
+ walk->action = ACTION_CONTINUE;
+ }
return 0;
}
@@ -61,8 +63,10 @@ static int ptdump_p4d_entry(p4d_t *p4d,
if (st->effective_prot)
st->effective_prot(st, 1, p4d_val(val));
- if (p4d_leaf(val))
+ if (p4d_leaf(val)) {
st->note_page(st, addr, 1, p4d_val(val));
+ walk->action = ACTION_CONTINUE;
+ }
return 0;
}
@@ -82,8 +86,10 @@ static int ptdump_pud_entry(pud_t *pud,
if (st->effective_prot)
st->effective_prot(st, 2, pud_val(val));
- if (pud_leaf(val))
+ if (pud_leaf(val)) {
st->note_page(st, addr, 2, pud_val(val));
+ walk->action = ACTION_CONTINUE;
+ }
return 0;
}
@@ -101,8 +107,10 @@ static int ptdump_pmd_entry(pmd_t *pmd,
if (st->effective_prot)
st->effective_prot(st, 3, pmd_val(val));
- if (pmd_leaf(val))
+ if (pmd_leaf(val)) {
st->note_page(st, addr, 3, pmd_val(val));
+ walk->action = ACTION_CONTINUE;
+ }
return 0;
}
--- a/mm/sparse-vmemmap.c~mm-sparsemem-use-page-table-lock-to-protect-kernel-pmd-operations
+++ a/mm/sparse-vmemmap.c
@@ -53,8 +53,7 @@ struct vmemmap_remap_walk {
struct list_head *vmemmap_pages;
};
-static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start,
- struct vmemmap_remap_walk *walk)
+static int __split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start)
{
pmd_t __pmd;
int i;
@@ -76,15 +75,34 @@ static int split_vmemmap_huge_pmd(pmd_t
set_pte_at(&init_mm, addr, pte, entry);
}
- /* Make pte visible before pmd. See comment in pmd_install(). */
- smp_wmb();
- pmd_populate_kernel(&init_mm, pmd, pgtable);
-
- flush_tlb_kernel_range(start, start + PMD_SIZE);
+ spin_lock(&init_mm.page_table_lock);
+ if (likely(pmd_leaf(*pmd))) {
+ /* Make pte visible before pmd. See comment in pmd_install(). */
+ smp_wmb();
+ pmd_populate_kernel(&init_mm, pmd, pgtable);
+ flush_tlb_kernel_range(start, start + PMD_SIZE);
+ } else {
+ pte_free_kernel(&init_mm, pgtable);
+ }
+ spin_unlock(&init_mm.page_table_lock);
return 0;
}
+static int split_vmemmap_huge_pmd(pmd_t *pmd, unsigned long start)
+{
+ int leaf;
+
+ spin_lock(&init_mm.page_table_lock);
+ leaf = pmd_leaf(*pmd);
+ spin_unlock(&init_mm.page_table_lock);
+
+ if (!leaf)
+ return 0;
+
+ return __split_vmemmap_huge_pmd(pmd, start);
+}
+
static void vmemmap_pte_range(pmd_t *pmd, unsigned long addr,
unsigned long end,
struct vmemmap_remap_walk *walk)
@@ -121,13 +139,12 @@ static int vmemmap_pmd_range(pud_t *pud,
pmd = pmd_offset(pud, addr);
do {
- if (pmd_leaf(*pmd)) {
- int ret;
+ int ret;
+
+ ret = split_vmemmap_huge_pmd(pmd, addr & PMD_MASK);
+ if (ret)
+ return ret;
- ret = split_vmemmap_huge_pmd(pmd, addr & PMD_MASK, walk);
- if (ret)
- return ret;
- }
next = pmd_addr_end(addr, end);
vmemmap_pte_range(pmd, addr, next, walk);
} while (pmd++, addr = next, addr != end);
@@ -321,10 +338,8 @@ int vmemmap_remap_free(unsigned long sta
*/
BUG_ON(start - reuse != PAGE_SIZE);
- mmap_write_lock(&init_mm);
+ mmap_read_lock(&init_mm);
ret = vmemmap_remap_range(reuse, end, &walk);
- mmap_write_downgrade(&init_mm);
-
if (ret && walk.nr_walked) {
end = reuse + walk.nr_walked * PAGE_SIZE;
/*
_
Patches currently in -mm which might be from songmuchun@xxxxxxxxxxxxx are
mm-slab-make-slab-iterator-functions-static.patch
mm-memcontrol-make-cgroup_memory_nokmem-static.patch
mm-hugetlb-free-the-2nd-vmemmap-page-associated-with-each-hugetlb-page.patch
mm-hugetlb-replace-hugetlb_free_vmemmap_enabled-with-a-static_key.patch
mm-sparsemem-use-page-table-lock-to-protect-kernel-pmd-operations.patch
selftests-vm-add-a-hugetlb-test-case.patch
mm-sparsemem-move-vmemmap-related-to-hugetlb-to-config_hugetlb_page_free_vmemmap.patch
fs-proc-store-pde-data-into-inode-i_private.patch
fs-proc-replace-pde_datainode-with-inode-i_private.patch
fs-proc-remove-pde_data.patch
fs-proc-use-define_proc_show_attribute-to-simplify-the-code.patch
