[PATCH v2 0/5] Cleanup and fixup for hugetlb

[PATCH v2 0/5] Cleanup and fixup for hugetlb

[Miaohe Lin]

Hi all,
This series contains cleanups to remove redundant VM_BUG_ON() and
simplify the return code. Also this handles the error case in
hugetlb_fix_reserve_counts() correctly. More details can be found
in the respective changelogs. Thanks!

v1->v2:
  collect Reviewed-by tag
  remove the HPAGE_RESV_OWNER check per Mike
  add a comment to hugetlb_unreserve_pages per Mike
  expand warning message a bit for hugetlb_fix_reserve_counts
  Add a new patch to remove unused variable
  Many thanks for Mike's review and suggestion!

Miaohe Lin (5):
  mm/hugeltb: remove redundant VM_BUG_ON() in region_add()
  mm/hugeltb: simplify the return code of __vma_reservation_common()
  mm/hugeltb: clarify (chg - freed) won't go negative in
    hugetlb_unreserve_pages()
  mm/hugeltb: handle the error case in hugetlb_fix_reserve_counts()
  mm/hugetlb: remove unused variable pseudo_vma in
    remove_inode_hugepages()

 fs/hugetlbfs/inode.c |  3 ---
 mm/hugetlb.c         | 57 +++++++++++++++++++++++++-------------------
 2 files changed, 33 insertions(+), 27 deletions(-)

-- 
2.19.1

[PATCH v2 1/5] mm/hugeltb: remove redundant VM_BUG_ON() in region_add()

[Miaohe Lin]

The same VM_BUG_ON() check is already done in the callee. Remove this extra
one to simplify the code slightly.

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/hugetlb.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index c22111f3da20..a03a50b7c410 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -556,7 +556,6 @@ static long region_add(struct resv_map *resv, long f, long t,
 	resv->adds_in_progress -= in_regions_needed;
 
 	spin_unlock(&resv->lock);
-	VM_BUG_ON(add < 0);
 	return add;
 }
 
-- 
2.19.1

[PATCH v2 2/5] mm/hugeltb: simplify the return code of __vma_reservation_common()

[Miaohe Lin]

It's guaranteed that the vma is associated with a resv_map, i.e. either
VM_MAYSHARE or HPAGE_RESV_OWNER, when the code reaches here or we would
have returned via !resv check above. So it's unneeded to check whether
HPAGE_RESV_OWNER is set here. Simplify the return code to make it more
clear.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/hugetlb.c | 41 ++++++++++++++++++++---------------------
 1 file changed, 20 insertions(+), 21 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a03a50b7c410..9b4c05699a90 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2163,27 +2163,26 @@ static long __vma_reservation_common(struct hstate *h,
 
 	if (vma->vm_flags & VM_MAYSHARE)
 		return ret;
-	else if (is_vma_resv_set(vma, HPAGE_RESV_OWNER) && ret >= 0) {
-		/*
-		 * In most cases, reserves always exist for private mappings.
-		 * However, a file associated with mapping could have been
-		 * hole punched or truncated after reserves were consumed.
-		 * As subsequent fault on such a range will not use reserves.
-		 * Subtle - The reserve map for private mappings has the
-		 * opposite meaning than that of shared mappings.  If NO
-		 * entry is in the reserve map, it means a reservation exists.
-		 * If an entry exists in the reserve map, it means the
-		 * reservation has already been consumed.  As a result, the
-		 * return value of this routine is the opposite of the
-		 * value returned from reserve map manipulation routines above.
-		 */
-		if (ret)
-			return 0;
-		else
-			return 1;
-	}
-	else
-		return ret < 0 ? ret : 0;
+	/*
+	 * We know private mapping must have HPAGE_RESV_OWNER set.
+	 *
+	 * In most cases, reserves always exist for private mappings.
+	 * However, a file associated with mapping could have been
+	 * hole punched or truncated after reserves were consumed.
+	 * As subsequent fault on such a range will not use reserves.
+	 * Subtle - The reserve map for private mappings has the
+	 * opposite meaning than that of shared mappings.  If NO
+	 * entry is in the reserve map, it means a reservation exists.
+	 * If an entry exists in the reserve map, it means the
+	 * reservation has already been consumed.  As a result, the
+	 * return value of this routine is the opposite of the
+	 * value returned from reserve map manipulation routines above.
+	 */
+	if (ret > 0)
+		return 0;
+	if (ret == 0)
+		return 1;
+	return ret;
 }
 
 static long vma_needs_reservation(struct hstate *h,
-- 
2.19.1

Re: [PATCH v2 2/5] mm/hugeltb: simplify the return code of __vma_reservation_common()

[Mike Kravetz]

On 4/10/21 12:23 AM, Miaohe Lin wrote:
> It's guaranteed that the vma is associated with a resv_map, i.e. either
> VM_MAYSHARE or HPAGE_RESV_OWNER, when the code reaches here or we would
> have returned via !resv check above. So it's unneeded to check whether
> HPAGE_RESV_OWNER is set here. Simplify the return code to make it more
> clear.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>

Thanks,

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
-- 
Mike Kravetz

[PATCH v2 3/5] mm/hugeltb: clarify (chg - freed) won't go negative in hugetlb_unreserve_pages()

[Miaohe Lin]

The resv_map could be NULL since this routine can be called in the evict
inode path for all hugetlbfs inodes and we will have chg = 0 in this case.
But (chg - freed) won't go negative as Mike pointed out:

 "If resv_map is NULL, then no hugetlb pages can be allocated/associated
  with the file.  As a result, remove_inode_hugepages will never find any
  huge pages associated with the inode and the passed value 'freed' will
  always be zero."

Add a comment clarifying this to make it clear and also avoid confusion.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/hugetlb.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 9b4c05699a90..387c9a62615e 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5435,6 +5435,9 @@ long hugetlb_unreserve_pages(struct inode *inode, long start, long end,
 	/*
 	 * If the subpool has a minimum size, the number of global
 	 * reservations to be released may be adjusted.
+	 *
+	 * Note that !resv_map implies freed == 0. So (chg - freed)
+	 * won't go negative.
 	 */
 	gbl_reserve = hugepage_subpool_put_pages(spool, (chg - freed));
 	hugetlb_acct_memory(h, -gbl_reserve);
-- 
2.19.1

Re: [PATCH v2 3/5] mm/hugeltb: clarify (chg - freed) won't go negative in hugetlb_unreserve_pages()

[Mike Kravetz]

On 4/10/21 12:23 AM, Miaohe Lin wrote:
> The resv_map could be NULL since this routine can be called in the evict
> inode path for all hugetlbfs inodes and we will have chg = 0 in this case.
> But (chg - freed) won't go negative as Mike pointed out:
> 
>  "If resv_map is NULL, then no hugetlb pages can be allocated/associated
>   with the file.  As a result, remove_inode_hugepages will never find any
>   huge pages associated with the inode and the passed value 'freed' will
>   always be zero."
> 
> Add a comment clarifying this to make it clear and also avoid confusion.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>

Thanks,

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
-- 
Mike Kravetz

[PATCH v2 4/5] mm/hugeltb: handle the error case in hugetlb_fix_reserve_counts()

[Miaohe Lin]

A rare out of memory error would prevent removal of the reserve map region
for a page. hugetlb_fix_reserve_counts() handles this rare case to avoid
dangling with incorrect counts. Unfortunately, hugepage_subpool_get_pages
and hugetlb_acct_memory could possibly fail too. We should correctly handle
these cases.

Fixes: b5cec28d36f5 ("hugetlbfs: truncate_hugepages() takes a range of pages")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/hugetlb.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 387c9a62615e..a14bb1a03ee4 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -745,13 +745,20 @@ void hugetlb_fix_reserve_counts(struct inode *inode)
 {
 	struct hugepage_subpool *spool = subpool_inode(inode);
 	long rsv_adjust;
+	bool reserved = false;
 
 	rsv_adjust = hugepage_subpool_get_pages(spool, 1);
-	if (rsv_adjust) {
+	if (rsv_adjust > 0) {
 		struct hstate *h = hstate_inode(inode);
 
-		hugetlb_acct_memory(h, 1);
+		if (!hugetlb_acct_memory(h, 1))
+			reserved = true;
+	} else if (!rsv_adjust) {
+		reserved = true;
 	}
+
+	if (!reserved)
+		pr_warn("hugetlb: Huge Page Reserved count may go negative.\n");
 }
 
 /*
-- 
2.19.1

Re: [PATCH v2 4/5] mm/hugeltb: handle the error case in hugetlb_fix_reserve_counts()

[Mike Kravetz]

On 4/10/21 12:23 AM, Miaohe Lin wrote:
> A rare out of memory error would prevent removal of the reserve map region
> for a page. hugetlb_fix_reserve_counts() handles this rare case to avoid
> dangling with incorrect counts. Unfortunately, hugepage_subpool_get_pages
> and hugetlb_acct_memory could possibly fail too. We should correctly handle
> these cases.
> 
> Fixes: b5cec28d36f5 ("hugetlbfs: truncate_hugepages() takes a range of pages")
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>

Thanks,

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
-- 
Mike Kravetz

[PATCH v2 5/5] mm/hugetlb: remove unused variable pseudo_vma in remove_inode_hugepages()

[Miaohe Lin]

The local variable pseudo_vma is not used anymore.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 fs/hugetlbfs/inode.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index d81f52b87bd7..a2a42335e8fd 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -463,14 +463,11 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
 	struct address_space *mapping = &inode->i_data;
 	const pgoff_t start = lstart >> huge_page_shift(h);
 	const pgoff_t end = lend >> huge_page_shift(h);
-	struct vm_area_struct pseudo_vma;
 	struct pagevec pvec;
 	pgoff_t next, index;
 	int i, freed = 0;
 	bool truncate_op = (lend == LLONG_MAX);
 
-	vma_init(&pseudo_vma, current->mm);
-	pseudo_vma.vm_flags = (VM_HUGETLB | VM_MAYSHARE | VM_SHARED);
 	pagevec_init(&pvec);
 	next = start;
 	while (next < end) {
-- 
2.19.1

Re: [PATCH v2 5/5] mm/hugetlb: remove unused variable pseudo_vma in remove_inode_hugepages()

[Mike Kravetz]

On 4/10/21 12:23 AM, Miaohe Lin wrote:
> The local variable pseudo_vma is not used anymore.
> 
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>

Thanks,

That should have been removed with 1b426bac66e6 ("hugetlb: use same fault
hash key for shared and private mappings").

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
-- 
Mike Kravetz

Re: [PATCH v2 5/5] mm/hugetlb: remove unused variable pseudo_vma in remove_inode_hugepages()

[Miaohe Lin]

On 2021/4/13 2:51, Mike Kravetz wrote:
> On 4/10/21 12:23 AM, Miaohe Lin wrote:
>> The local variable pseudo_vma is not used anymore.
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> 
> Thanks,
> 
> That should have been removed with 1b426bac66e6 ("hugetlb: use same fault
> hash key for shared and private mappings").
> 

Yep. Many thanks for Reviewed-by tag! :)

> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
>