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authorMuchun Song <songmuchun@bytedance.com>2022-03-23 00:45:06 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2022-03-23 01:57:08 +0300
commitd8d55f5616cf3b900a23a72dd24e7b07211e7859 (patch)
tree569325ac86f93106d5329c40e6bb0d5c487d53e5 /mm/sparse-vmemmap.c
parenta6b40850c442bf996e729e1d441d3dbc37cea171 (diff)
downloadlinux-d8d55f5616cf3b900a23a72dd24e7b07211e7859.tar.xz
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@bytedance.com Signed-off-by: Muchun Song <songmuchun@bytedance.com> Cc: Barry Song <song.bao.hua@hisilicon.com> Cc: Bodeddula Balasubramaniam <bodeddub@amazon.com> Cc: Chen Huang <chenhuang5@huawei.com> Cc: David Hildenbrand <david@redhat.com> Cc: Fam Zheng <fam.zheng@bytedance.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Matthew Wilcox <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Qi Zheng <zhengqi.arch@bytedance.com> Cc: Xiongchun Duan <duanxiongchun@bytedance.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/sparse-vmemmap.c')
-rw-r--r--mm/sparse-vmemmap.c47
1 files changed, 31 insertions, 16 deletions
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index e881f5db7091..c64d1aa3c4b5 100644
--- a/mm/sparse-vmemmap.c
+++ b/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 *pmd, unsigned long start,
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, unsigned long addr,
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 start, unsigned long end,
*/
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;
/*