[PATCH 1/2] MADVISE_FREE, THP: Fix madvise_free_huge_pmd return value after splitting

[PATCH 1/2] MADVISE_FREE, THP: Fix madvise_free_huge_pmd return value after splitting

[Huang, Ying]

From: Huang Ying <ying.huang@intel.com>

madvise_free_huge_pmd should return 0 if the fallback PTE operations are
required.  In madvise_free_huge_pmd, if part pages of THP are discarded,
the THP will be split and fallback PTE operations should be used if
splitting succeeds.  But the original code will make fallback PTE
operations skipped, after splitting succeeds.  Fix that via make
madvise_free_huge_pmd return 0 after splitting successfully, so that the
fallback PTE operations will be done.

Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
---
 mm/huge_memory.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 848c16c..546cd21 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1287,14 +1287,9 @@ int madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 	if (next - addr != HPAGE_PMD_SIZE) {
 		get_page(page);
 		spin_unlock(ptl);
-		if (split_huge_page(page)) {
-			put_page(page);
-			unlock_page(page);
-			goto out_unlocked;
-		}
+		split_huge_page(page);
 		put_page(page);
 		unlock_page(page);
-		ret = 1;
 		goto out_unlocked;
 	}
 
-- 
2.8.1

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[PATCH 2/2] mm, THP: Clean up return value of madvise_free_huge_pmd

[Huang, Ying]

From: Huang Ying <ying.huang@intel.com>

The definition of return value of madvise_free_huge_pmd is not clear
before.  According to the suggestion of Minchan Kim, change the type of
return value to bool and return true if we do MADV_FREE successfully on
entire pmd page, otherwise, return false.  Comments are added too.

Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
---
 include/linux/huge_mm.h |  2 +-
 mm/huge_memory.c        | 15 ++++++++-------
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index eb81081..db97784 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -11,7 +11,7 @@ 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,
+extern bool madvise_free_huge_pmd(struct mmu_gather *tlb,
 			struct vm_area_struct *vma,
 			pmd_t *pmd, unsigned long addr, unsigned long next);
 extern int zap_huge_pmd(struct mmu_gather *tlb,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 546cd21..d2a5224 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1249,25 +1249,26 @@ out:
 	return 0;
 }
 
-int madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
+/*
+ * Return true if we do MADV_FREE successfully on entire pmd page.
+ * Otherwise, return false.
+ */
+bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 		pmd_t *pmd, unsigned long addr, unsigned long next)
-
 {
 	spinlock_t *ptl;
 	pmd_t orig_pmd;
 	struct page *page;
 	struct mm_struct *mm = tlb->mm;
-	int ret = 0;
+	bool ret = false;
 
 	ptl = pmd_trans_huge_lock(pmd, vma);
 	if (!ptl)
 		goto out_unlocked;
 
 	orig_pmd = *pmd;
-	if (is_huge_zero_pmd(orig_pmd)) {
-		ret = 1;
+	if (is_huge_zero_pmd(orig_pmd))
 		goto out;
-	}
 
 	page = pmd_page(orig_pmd);
 	/*
@@ -1309,7 +1310,7 @@ int madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 		set_pmd_at(mm, addr, pmd, orig_pmd);
 		tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
 	}
-	ret = 1;
+	ret = true;
 out:
 	spin_unlock(ptl);
 out_unlocked:
-- 
2.8.1

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Re: [PATCH 1/2] MADVISE_FREE, THP: Fix madvise_free_huge_pmd return value after splitting

[Minchan Kim]

On Tue, Jun 28, 2016 at 10:36:29AM -0700, Huang, Ying wrote:
> From: Huang Ying <ying.huang@intel.com>
> 
> madvise_free_huge_pmd should return 0 if the fallback PTE operations are
> required.  In madvise_free_huge_pmd, if part pages of THP are discarded,
> the THP will be split and fallback PTE operations should be used if
> splitting succeeds.  But the original code will make fallback PTE
> operations skipped, after splitting succeeds.  Fix that via make
> madvise_free_huge_pmd return 0 after splitting successfully, so that the
> fallback PTE operations will be done.
> 
> Cc: Minchan Kim <minchan@kernel.org>
> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Acked-by: Minchan Kim <minchan@kernel.org>

Thanks!

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Re: [PATCH 2/2] mm, THP: Clean up return value of madvise_free_huge_pmd

[Minchan Kim]

On Tue, Jun 28, 2016 at 10:36:30AM -0700, Huang, Ying wrote:
> From: Huang Ying <ying.huang@intel.com>
> 
> The definition of return value of madvise_free_huge_pmd is not clear
> before.  According to the suggestion of Minchan Kim, change the type of
> return value to bool and return true if we do MADV_FREE successfully on
> entire pmd page, otherwise, return false.  Comments are added too.
> 
> Cc: Minchan Kim <minchan@kernel.org>
> Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Acked-by: Minchan Kim <minchan@kernel.org>

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