hfs-replace-kmap-with-kmap_local_page-in-btreec.patch removed from -mm tree

merged mm-nonmm-stable Andrew Morton 1 participant 1 message Sep 12, 2022

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Andrew Morton

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2022-09-12 04:57 UTC #0 lore raw

The quilt patch titled
Subject: hfs: replace kmap() with kmap_local_page() in btree.c
has been removed from the -mm tree. Its filename was
hfs-replace-kmap-with-kmap_local_page-in-btreec.patch

This patch was dropped because it was merged into the mm-nonmm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: "Fabio M. De Francesco" <[email protected]>
Subject: hfs: replace kmap() with kmap_local_page() in btree.c
Date: Sun, 21 Aug 2022 20:04:00 +0200

kmap() is being deprecated in favor of kmap_local_page().

Two main problems with kmap(): (1) It comes with an overhead as mapping space is restricted and protected by a global lock for synchronization and
(2) it also requires global TLB invalidation when the kmap's pool wraps and it might block when the mapping space is fully utilized until a slot becomes available.

With kmap_local_page() the mappings are per thread, CPU local, can take page faults, and can be called from any context (including interrupts). It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore, the tasks can be preempted and, when they are scheduled to run again, the kernel virtual addresses are restored and still valid.

Since its use in btree.c is safe everywhere, it should be preferred.

Therefore, replace kmap() with kmap_local_page() in btree.c. Where possible, use the suited standard helpers (memzero_page(), memcpy_page()) instead of open coding kmap_local_page() plus memset() or memcpy().

Tested in a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel with HIGHMEM64GB enabled.

Link https://lkml.kernel.org/r/[email protected] open here

Signed-off-by Fabio M. De Francesco <[email protected]>

Suggested-by Ira Weiny <[email protected]>

Reviewed-by Viacheslav Dubeyko <[email protected]>

Cc Arnd Bergmann <[email protected]>

Cc Chaitanya Kulkarni <[email protected]>

Cc Christian Brauner (Microsoft) <[email protected]>

Cc Damien Le Moal <[email protected]>

Cc Jeff Layton <[email protected]>

Cc Jens Axboe <[email protected]>

Cc Kees Cook <[email protected]>

Cc Martin K. Petersen <[email protected]>

Cc Matthew Wilcox <[email protected]>

Cc Muchun Song <[email protected]>

Cc Roman Gushchin <[email protected]>

Cc Theodore Ts'o <[email protected]>

Signed-off-by Andrew Morton <[email protected]>

---

 fs/hfs/btree.c |   30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

fs/hfs/btree.c renamed from fs/hfs/btree.c~hfs-replace-kmap-with-kmap_local_page-in-btreec +16 ~~-14~~

@@ -80,7 +80,8 @@ struct hfs_btree *hfs_btree_open(struct
 		goto free_inode;
 
 	/* Load the header */
-	head = (struct hfs_btree_header_rec *)(kmap(page) + sizeof(struct hfs_bnode_desc));
+	head = (struct hfs_btree_header_rec *)(kmap_local_page(page) +
+					       sizeof(struct hfs_bnode_desc));
 	tree->root = be32_to_cpu(head->root);
 	tree->leaf_count = be32_to_cpu(head->leaf_count);
 	tree->leaf_head = be32_to_cpu(head->leaf_head);

@@ -119,12 +120,12 @@ struct hfs_btree *hfs_btree_open(struct
 	tree->node_size_shift = ffs(size) - 1;
 	tree->pages_per_bnode = (tree->node_size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 
-	kunmap(page);
+	kunmap_local(head);
 	put_page(page);
 	return tree;
 
 fail_page:
-	kunmap(page);
+	kunmap_local(head);
 	put_page(page);
 free_inode:
 	tree->inode->i_mapping->a_ops = &hfs_aops;

@@ -170,7 +171,8 @@ void hfs_btree_write(struct hfs_btree *t
 		return;
 	/* Load the header */
 	page = node->page[0];
-	head = (struct hfs_btree_header_rec *)(kmap(page) + sizeof(struct hfs_bnode_desc));
+	head = (struct hfs_btree_header_rec *)(kmap_local_page(page) +
+					       sizeof(struct hfs_bnode_desc));
 
 	head->root = cpu_to_be32(tree->root);
 	head->leaf_count = cpu_to_be32(tree->leaf_count);

@@ -181,7 +183,7 @@ void hfs_btree_write(struct hfs_btree *t
 	head->attributes = cpu_to_be32(tree->attributes);
 	head->depth = cpu_to_be16(tree->depth);
 
-	kunmap(page);
+	kunmap_local(head);
 	set_page_dirty(page);
 	hfs_bnode_put(node);
 }

@@ -269,7 +271,7 @@ struct hfs_bnode *hfs_bmap_alloc(struct
 
 	off += node->page_offset;
 	pagep = node->page + (off >> PAGE_SHIFT);
-	data = kmap(*pagep);
+	data = kmap_local_page(*pagep);
 	off &= ~PAGE_MASK;
 	idx = 0;

@@ -282,7 +284,7 @@ struct hfs_bnode *hfs_bmap_alloc(struct
 						idx += i;
 						data[off] |= m;
 						set_page_dirty(*pagep);
-						kunmap(*pagep);
+						kunmap_local(data);
 						tree->free_nodes--;
 						mark_inode_dirty(tree->inode);
 						hfs_bnode_put(node);

@@ -291,14 +293,14 @@ struct hfs_bnode *hfs_bmap_alloc(struct
 				}
 			}
 			if (++off >= PAGE_SIZE) {
-				kunmap(*pagep);
-				data = kmap(*++pagep);
+				kunmap_local(data);
+				data = kmap_local_page(*++pagep);
 				off = 0;
 			}
 			idx += 8;
 			len--;
 		}
-		kunmap(*pagep);
+		kunmap_local(data);
 		nidx = node->next;
 		if (!nidx) {
 			printk(KERN_DEBUG "create new bmap node...\n");

@@ -314,7 +316,7 @@ struct hfs_bnode *hfs_bmap_alloc(struct
 		off = off16;
 		off += node->page_offset;
 		pagep = node->page + (off >> PAGE_SHIFT);
-		data = kmap(*pagep);
+		data = kmap_local_page(*pagep);
 		off &= ~PAGE_MASK;
 	}
 }

@@ -361,20 +363,20 @@ void hfs_bmap_free(struct hfs_bnode *nod
 	}
 	off += node->page_offset + nidx / 8;
 	page = node->page[off >> PAGE_SHIFT];
-	data = kmap(page);
+	data = kmap_local_page(page);
 	off &= ~PAGE_MASK;
 	m = 1 << (~nidx & 7);
 	byte = data[off];
 	if (!(byte & m)) {
 		pr_crit("trying to free free bnode %u(%d)\n",
 			node->this, node->type);
-		kunmap(page);
+		kunmap_local(data);
 		hfs_bnode_put(node);
 		return;
 	}
 	data[off] = byte & ~m;
 	set_page_dirty(page);
-	kunmap(page);
+	kunmap_local(data);
 	hfs_bnode_put(node);
 	tree->free_nodes++;
 	mark_inode_dirty(tree->inode);

Patches currently in -mm which might be from [email protected] are