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Subject[PATCH v12 8/8] mm: Don't split THP page when syscall is called
Date
We don't need to split THP page when MADV_FREE syscall is
called. It could be done when VM decide really frees it so
we could avoid unnecessary THP split.

Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
include/linux/huge_mm.h | 4 ++++
mm/huge_memory.c | 35 +++++++++++++++++++++++++++++++++++
mm/madvise.c | 21 ++++++++++++++++++++-
mm/rmap.c | 8 ++++++--
mm/vmscan.c | 28 ++++++++++++++++++----------
5 files changed, 83 insertions(+), 13 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 63579cb8d3dc..25a961256d9f 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -19,6 +19,9 @@ extern struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
unsigned long addr,
pmd_t *pmd,
unsigned int flags);
+extern int madvise_free_huge_pmd(struct mmu_gather *tlb,
+ struct vm_area_struct *vma,
+ pmd_t *pmd, unsigned long addr);
extern int zap_huge_pmd(struct mmu_gather *tlb,
struct vm_area_struct *vma,
pmd_t *pmd, unsigned long addr);
@@ -56,6 +59,7 @@ extern pmd_t *page_check_address_pmd(struct page *page,
unsigned long address,
enum page_check_address_pmd_flag flag,
spinlock_t **ptl);
+extern int pmd_freeable(pmd_t pmd);

#define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
#define HPAGE_PMD_NR (1<<HPAGE_PMD_ORDER)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 5d562a9fe931..919c780015b8 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1384,6 +1384,36 @@ out:
return 0;
}

+int madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
+ pmd_t *pmd, unsigned long addr)
+
+{
+ spinlock_t *ptl;
+ struct mm_struct *mm = tlb->mm;
+ int ret = 1;
+
+ if (pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
+ struct page *page;
+ pmd_t orig_pmd;
+
+ orig_pmd = pmdp_get_and_clear(mm, addr, pmd);
+
+ /* No hugepage in swapcache */
+ page = pmd_page(orig_pmd);
+ VM_BUG_ON_PAGE(PageSwapCache(page), page);
+
+ orig_pmd = pmd_mkold(orig_pmd);
+ orig_pmd = pmd_mkclean(orig_pmd);
+
+ set_pmd_at(mm, addr, pmd, orig_pmd);
+ tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
+ spin_unlock(ptl);
+ ret = 0;
+ }
+
+ return ret;
+}
+
int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
pmd_t *pmd, unsigned long addr)
{
@@ -1620,6 +1650,11 @@ unlock:
return NULL;
}

+int pmd_freeable(pmd_t pmd)
+{
+ return !pmd_dirty(pmd);
+}
+
static int __split_huge_page_splitting(struct page *page,
struct vm_area_struct *vma,
unsigned long address)
diff --git a/mm/madvise.c b/mm/madvise.c
index 55b42e5e32a3..0927eba6d858 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -271,8 +271,26 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
spinlock_t *ptl;
pte_t *pte, ptent;
struct page *page;
+ unsigned long next;
+
+ next = pmd_addr_end(addr, end);
+ if (pmd_trans_huge(*pmd)) {
+ if (next - addr != HPAGE_PMD_SIZE) {
+#ifdef CONFIG_DEBUG_VM
+ if (!rwsem_is_locked(&mm->mmap_sem)) {
+ pr_err("%s: mmap_sem is unlocked! addr=0x%lx end=0x%lx vma->vm_start=0x%lx vma->vm_end=0x%lx\n",
+ __func__, addr, end,
+ vma->vm_start,
+ vma->vm_end);
+ BUG();
+ }
+#endif
+ split_huge_page_pmd(vma, addr, pmd);
+ } else if (!madvise_free_huge_pmd(tlb, vma, pmd, addr))
+ goto next;
+ /* fall through */
+ }

- split_huge_page_pmd(vma, addr, pmd);
if (pmd_trans_unstable(pmd))
return 0;

@@ -312,6 +330,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
}
arch_leave_lazy_mmu_mode();
pte_unmap_unlock(pte - 1, ptl);
+next:
cond_resched();
return 0;
}
diff --git a/mm/rmap.c b/mm/rmap.c
index 7ac6e059aba7..5a0cca9bc263 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -704,9 +704,13 @@ static int page_referenced_one(struct page *page, struct vm_area_struct *vma,
referenced++;

/*
- * In this implmentation, MADV_FREE doesn't support THP free
+ * Use pmd_freeable instead of raw pmd_dirty because in some
+ * of architecture, pmd_dirty is not defined unless
+ * CONFIG_TRANSPARNTE_HUGE is enabled
*/
- dirty++;
+ if (!pmd_freeable(*pmd))
+ dirty++;
+
spin_unlock(ptl);
} else {
pte_t *pte;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 914815a43362..995b28e3aee7 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -971,17 +971,25 @@ static unsigned long shrink_page_list(struct list_head *page_list,
* Anonymous process memory has backing store?
* Try to allocate it some swap space here.
*/
- if (PageAnon(page) && !PageSwapCache(page) && !freeable) {
- if (!(sc->gfp_mask & __GFP_IO))
- goto keep_locked;
- if (!add_to_swap(page, page_list))
- goto activate_locked;
- may_enter_fs = 1;
-
- /* Adding to swap updated mapping */
- mapping = page_mapping(page);
+ if (PageAnon(page) && !PageSwapCache(page)) {
+ if (!freeable) {
+ if (!(sc->gfp_mask & __GFP_IO))
+ goto keep_locked;
+ if (!add_to_swap(page, page_list))
+ goto activate_locked;
+ may_enter_fs = 1;
+ /* Adding to swap updated mapping */
+ mapping = page_mapping(page);
+ } else {
+ if (likely(!PageTransHuge(page)))
+ goto unmap;
+ /* try_to_unmap isn't aware of THP page */
+ if (unlikely(split_huge_page_to_list(page,
+ page_list)))
+ goto keep_locked;
+ }
}
-
+unmap:
/*
* The page is mapped into the page tables of one or more
* processes. Try to unmap it here.
--
2.0.0


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