From 9f25f357c557bfea39a2d6a629a6317d2b3dfc64 Mon Sep 17 00:00:00 2001 From: "Fabio M. De Francesco" Date: Tue, 9 Aug 2022 22:31:05 +0200 Subject: [PATCH] hfsplus: convert kmap() to kmap_local_page() in btree.c kmap() is being deprecated in favor of kmap_local_page(). There are 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 are 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. Tested in a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel with HIGHMEM64GB enabled. Link: https://lkml.kernel.org/r/20220809203105.26183-5-fmdefrancesco@gmail.com Signed-off-by: Fabio M. De Francesco Suggested-by: Ira Weiny Reviewed-by: Ira Weiny Reviewed-by: Viacheslav Dubeyko Cc: Bart Van Assche Cc: Jens Axboe Cc: Kees Cook Cc: Matthew Wilcox Cc: Muchun Song Signed-off-by: Andrew Morton --- fs/hfsplus/btree.c | 28 ++++++++++++++-------------- 1 file changed, 14 insertions(+), 14 deletions(-) diff --git a/fs/hfsplus/btree.c b/fs/hfsplus/btree.c index 3a917a9a4edd..9e1732a2b92a 100644 --- a/fs/hfsplus/btree.c +++ b/fs/hfsplus/btree.c @@ -163,7 +163,7 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id) goto free_inode; /* Load the header */ - head = (struct hfs_btree_header_rec *)(kmap(page) + + 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); @@ -240,12 +240,12 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id) (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 = &hfsplus_aops; @@ -292,7 +292,7 @@ int hfs_btree_write(struct hfs_btree *tree) return -EIO; /* Load the header */ page = node->page[0]; - head = (struct hfs_btree_header_rec *)(kmap(page) + + head = (struct hfs_btree_header_rec *)(kmap_local_page(page) + sizeof(struct hfs_bnode_desc)); head->root = cpu_to_be32(tree->root); @@ -304,7 +304,7 @@ int hfs_btree_write(struct hfs_btree *tree) 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); return 0; @@ -395,7 +395,7 @@ struct hfs_bnode *hfs_bmap_alloc(struct hfs_btree *tree) off += node->page_offset; pagep = node->page + (off >> PAGE_SHIFT); - data = kmap(*pagep); + data = kmap_local_page(*pagep); off &= ~PAGE_MASK; idx = 0; @@ -408,7 +408,7 @@ struct hfs_bnode *hfs_bmap_alloc(struct hfs_btree *tree) 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); @@ -418,14 +418,14 @@ struct hfs_bnode *hfs_bmap_alloc(struct hfs_btree *tree) } } 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) { hfs_dbg(BNODE_MOD, "create new bmap node\n"); @@ -441,7 +441,7 @@ struct hfs_bnode *hfs_bmap_alloc(struct hfs_btree *tree) off = off16; off += node->page_offset; pagep = node->page + (off >> PAGE_SHIFT); - data = kmap(*pagep); + data = kmap_local_page(*pagep); off &= ~PAGE_MASK; } } @@ -491,7 +491,7 @@ void hfs_bmap_free(struct hfs_bnode *node) } 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]; @@ -499,13 +499,13 @@ void hfs_bmap_free(struct hfs_bnode *node) 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);