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hfs: replace kmap() with kmap_local_page() in btree.c 

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/20220821180400.8198-4-fmdefrancesco@gmail.com
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Suggested-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Chaitanya Kulkarni <kch@nvidia.com>
Cc: Christian Brauner (Microsoft) <brauner@kernel.org>
Cc: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Kees Cook <keescook@chromium.org>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Fabio M. De Francesco 2022-08-21 20:04:00 +02:00 committed by Andrew Morton
parent ca0ac8dfd3
commit 21490eff12
1 changed files with 16 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

30
fs/hfs/btree.c
View File

@ -80,7 +80,8 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id, btree_keycmp ke
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 super_block *sb, u32 id, btree_keycmp ke
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 *tree)
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 *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);
}
@ -269,7 +271,7 @@ 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;
@ -282,7 +284,7 @@ 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);
@ -291,14 +293,14 @@ 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) {
printk(KERN_DEBUG "create new bmap node...\n");
@ -314,7 +316,7 @@ 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;
}
}
@ -361,20 +363,20 @@ 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];
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);