From: Liam R. Howlett <Liam.Howlett@oracle.com>
Date: Wed, 30 Mar 2022 17:35:49 +0000 (-0400)
Subject: mm: Change munmap splitting order and move_vma()
X-Git-Tag: remove_vma_adjust~10
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=b296886d490fa30d1b3ca8da8a095779985781f4;p=users%2Fjedix%2Flinux-maple.git

mm: Change munmap splitting order and move_vma()

Splitting can be more efficient when done in the reverse order to
minimize VMA walking.  Change do_mas_align_munmap() to reduce walking of
the tree during split operations.

move_vma() must also be altered to remove the dependency of keeping the
original VMA as the active part of the split.  Look up the new VMA or
two if necessary.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
---

diff --git a/mm/mmap.c b/mm/mmap.c
index 125e8903c93c..4d4149d2a9f1 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2308,14 +2308,7 @@ do_mas_align_munmap(struct ma_state *mas, struct vm_area_struct *vma,
 		return -ENOMEM;
 
 	mas->last = end - 1;
-	/*
-	 * If we need to split any vma, do it now to save pain later.
-	 *
-	 * Note: mremap's move_vma VM_ACCOUNT handling assumes a partially
-	 * unmapped vm_area_struct will remain in use: so lower split_vma
-	 * places tmp vma above, and higher split_vma places tmp vma below.
-	 */
-
+	/* If we need to split any vma, do it now to save pain later. */
 	/* Does it split the first one? */
 	if (start > vma->vm_start) {
 
@@ -2331,18 +2324,18 @@ do_mas_align_munmap(struct ma_state *mas, struct vm_area_struct *vma,
 		 * mas_pause() is not needed since mas->index needs to be set
 		 * differently than vma->vm_end anyways.
 		 */
-		error = __split_vma(mm, vma, start, 0);
+		error = __split_vma(mm, vma, start, 1);
 		if (error)
 			goto start_split_failed;
 
-		mas_set(mas, start);
-		vma = mas_walk(mas);
+		mas_set(mas, start - 1);
+		prev = mas_walk(mas);
+	} else {
+		prev = mas_prev(mas, 0);
+		if (unlikely((!prev)))
+			mas_set(mas, start);
 	}
 
-	prev = mas_prev(mas, 0);
-	if (unlikely((!prev)))
-		mas_set(mas, start);
-
 	/*
 	 * Detach a range of VMAs from the mm. Using next as a temp variable as
 	 * it is always overwritten.
@@ -2350,27 +2343,16 @@ do_mas_align_munmap(struct ma_state *mas, struct vm_area_struct *vma,
 	mas_for_each(mas, next, end - 1) {
 		/* Does it split the end? */
 		if (next->vm_end > end) {
-			struct vm_area_struct *split;
-
-			error = __split_vma(mm, next, end, 1);
+			error = __split_vma(mm, next, end, 0);
 			if (error)
 				goto end_split_failed;
 
 			mas_set(mas, end);
-			split = mas_prev(mas, 0);
-			error = munmap_sidetree(split, &mas_detach);
-			if (error)
-				goto munmap_sidetree_failed;
-
-			count++;
-			if (vma == next)
-				vma = split;
-			break;
 		}
+
 		error = munmap_sidetree(next, &mas_detach);
 		if (error)
 			goto munmap_sidetree_failed;
-
 		count++;
 #ifdef CONFIG_DEBUG_VM_MAPLE_TREE
 		BUG_ON(next->vm_start < start);
@@ -2378,9 +2360,7 @@ do_mas_align_munmap(struct ma_state *mas, struct vm_area_struct *vma,
 #endif
 	}
 
-	if (!next)
-		next = mas_next(mas, ULONG_MAX);
-
+	next = mas_find(mas, ULONG_MAX);
 	if (unlikely(uf)) {
 		/*
 		 * If userfaultfd_unmap_prep returns an error the vmas
diff --git a/mm/mremap.c b/mm/mremap.c
index e465ffe279bb..b7d56d6d34a4 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -580,9 +580,9 @@ static unsigned long move_vma(struct vm_area_struct *vma,
 	unsigned long vm_flags = vma->vm_flags;
 	unsigned long new_pgoff;
 	unsigned long moved_len;
-	unsigned long excess = 0;
+	unsigned long account_start = 0;
+	unsigned long account_end = 0;
 	unsigned long hiwater_vm;
-	int split = 0;
 	int err = 0;
 	bool need_rmap_locks;
 
@@ -662,10 +662,10 @@ static unsigned long move_vma(struct vm_area_struct *vma,
 	/* Conceal VM_ACCOUNT so old reservation is not undone */
 	if (vm_flags & VM_ACCOUNT && !(flags & MREMAP_DONTUNMAP)) {
 		vma->vm_flags &= ~VM_ACCOUNT;
-		excess = vma->vm_end - vma->vm_start - old_len;
-		if (old_addr > vma->vm_start &&
-		    old_addr + old_len < vma->vm_end)
-			split = 1;
+		if (vma->vm_start < old_addr)
+			account_start = vma->vm_start;
+		if (vma->vm_end > old_addr + old_len)
+			account_end = vma->vm_end - 1;
 	}
 
 	/*
@@ -704,7 +704,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
 		/* OOM: unable to split vma, just get accounts right */
 		if (vm_flags & VM_ACCOUNT && !(flags & MREMAP_DONTUNMAP))
 			vm_acct_memory(old_len >> PAGE_SHIFT);
-		excess = 0;
+		account_start = account_end = 0;
 	}
 
 	if (vm_flags & VM_LOCKED) {
@@ -715,10 +715,14 @@ static unsigned long move_vma(struct vm_area_struct *vma,
 	mm->hiwater_vm = hiwater_vm;
 
 	/* Restore VM_ACCOUNT if one or two pieces of vma left */
-	if (excess) {
+	if (account_start) {
+		vma = vma_lookup(mm, account_start);
+		vma->vm_flags |= VM_ACCOUNT;
+	}
+
+	if (account_end) {
+		vma = vma_lookup(mm, account_end);
 		vma->vm_flags |= VM_ACCOUNT;
-		if (split)
-			find_vma(mm, vma->vm_end)->vm_flags |= VM_ACCOUNT;
 	}
 
 	return new_addr;