Re: [PATCH v4] fs/ufs: Replace kmap() with kmap_local_page()
From: Ira Weiny
Date: Thu Sep 22 2022 - 11:56:11 EST
On Mon, Aug 22, 2022 at 04:44:20PM +0200, Fabio M. De Francesco wrote:
> kmap() is being deprecated in favor of kmap_local_page().
>
> There are two main problems with kmap(): (1) It comes with an overhead as
> the 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 fs/ufs is safe everywhere, it should be preferred.
>
> Therefore, replace kmap() with kmap_local_page() in fs/ufs. kunmap_local()
> requires the mapping address, so return that address from ufs_get_page()
> to be used in ufs_put_page(). Where suited, use the standard helper
> memzero_page() instead of open coding kmap_local_page() plus memset().
>
> These changes are essentially ported from fs/ext2 and are largely based on
> commit 782b76d7abdf ("fs/ext2: Replace kmap() with kmap_local_page()").
>
> Cc: "Venkataramanan, Anirudh" <anirudh.venkataramanan@xxxxxxxxx>
> Suggested-by: Ira Weiny <ira.weiny@xxxxxxxxx>
Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx>
> ---
>
> This code is not tested. I have no means to create an UFS filesystem.
> Despite nothing here seems to break the strict rules about the use of
> kmap_local_page(), any help with testing will be much appreciated :-)
>
> v3 -> v4: Convert another kmap() which was overlooked. Since the code
> changed, remove the "Reviewed-by" tag from Ira.
>
> v2 -> v3: Rename a variable for consistency (Ira Weiny). Add a
> "Reviewed-by" tag.
>
> v1 -> v2: Correct some style's issues reported by checkpatch.pl.
> Remove an "inline" compiler directive from fs/ufs/ufs.h,
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
>
> fs/ufs/dir.c | 116 +++++++++++++++++++++++++++++++------------------
> fs/ufs/namei.c | 38 ++++++++--------
> fs/ufs/ufs.h | 12 +++--
> 3 files changed, 102 insertions(+), 64 deletions(-)
>
> diff --git a/fs/ufs/dir.c b/fs/ufs/dir.c
> index 391efaf1d528..db7564852391 100644
> --- a/fs/ufs/dir.c
> +++ b/fs/ufs/dir.c
> @@ -61,9 +61,9 @@ static int ufs_commit_chunk(struct page *page, loff_t pos, unsigned len)
> return err;
> }
>
> -static inline void ufs_put_page(struct page *page)
> +inline void ufs_put_page(struct page *page, void *page_addr)
> {
> - kunmap(page);
> + kunmap_local(page_addr);
> put_page(page);
> }
>
> @@ -72,11 +72,12 @@ ino_t ufs_inode_by_name(struct inode *dir, const struct qstr *qstr)
> ino_t res = 0;
> struct ufs_dir_entry *de;
> struct page *page;
> -
> - de = ufs_find_entry(dir, qstr, &page);
> + void *page_addr;
> +
> + de = ufs_find_entry(dir, qstr, &page, &page_addr);
> if (de) {
> res = fs32_to_cpu(dir->i_sb, de->d_ino);
> - ufs_put_page(page);
> + ufs_put_page(page, page_addr);
> }
> return res;
> }
> @@ -84,11 +85,11 @@ ino_t ufs_inode_by_name(struct inode *dir, const struct qstr *qstr)
>
> /* Releases the page */
> void ufs_set_link(struct inode *dir, struct ufs_dir_entry *de,
> - struct page *page, struct inode *inode,
> - bool update_times)
> + struct page *page, void *page_addr,
> + struct inode *inode, bool update_times)
> {
> loff_t pos = page_offset(page) +
> - (char *) de - (char *) page_address(page);
> + (char *)de - (char *)page_addr;
> unsigned len = fs16_to_cpu(dir->i_sb, de->d_reclen);
> int err;
>
> @@ -100,18 +101,17 @@ void ufs_set_link(struct inode *dir, struct ufs_dir_entry *de,
> ufs_set_de_type(dir->i_sb, de, inode->i_mode);
>
> err = ufs_commit_chunk(page, pos, len);
> - ufs_put_page(page);
> + ufs_put_page(page, page_addr);
> if (update_times)
> dir->i_mtime = dir->i_ctime = current_time(dir);
> mark_inode_dirty(dir);
> }
>
>
> -static bool ufs_check_page(struct page *page)
> +static bool ufs_check_page(struct page *page, char *kaddr)
> {
> struct inode *dir = page->mapping->host;
> struct super_block *sb = dir->i_sb;
> - char *kaddr = page_address(page);
> unsigned offs, rec_len;
> unsigned limit = PAGE_SIZE;
> const unsigned chunk_mask = UFS_SB(sb)->s_uspi->s_dirblksize - 1;
> @@ -186,21 +186,28 @@ static bool ufs_check_page(struct page *page)
> return false;
> }
>
> -static struct page *ufs_get_page(struct inode *dir, unsigned long n)
> +/*
> + * Calls to ufs_get_page()/ufs_put_page() must be nested according to the
> + * rules documented in kmap_local_page()/kunmap_local().
> + *
> + * NOTE: ufs_find_entry() and ufs_dotdot() act as calls to ufs_get_page()
> + * and must be treated accordingly for nesting purposes.
> + */
> +static struct page *ufs_get_page(struct inode *dir, unsigned long n, void **page_addr)
> {
> struct address_space *mapping = dir->i_mapping;
> struct page *page = read_mapping_page(mapping, n, NULL);
> if (!IS_ERR(page)) {
> - kmap(page);
> + *page_addr = kmap_local_page(page);
> if (unlikely(!PageChecked(page))) {
> - if (!ufs_check_page(page))
> + if (!ufs_check_page(page, *page_addr))
> goto fail;
> }
> }
> return page;
>
> fail:
> - ufs_put_page(page);
> + ufs_put_page(page, *page_addr);
> return ERR_PTR(-EIO);
> }
>
> @@ -226,15 +233,29 @@ ufs_next_entry(struct super_block *sb, struct ufs_dir_entry *p)
> fs16_to_cpu(sb, p->d_reclen));
> }
>
> -struct ufs_dir_entry *ufs_dotdot(struct inode *dir, struct page **p)
> +/*
> + * Return the '..' directory entry and the page in which the entry was found
> + * (as a parameter - p).
> + *
> + * On Success ufs_put_page() should be called on *p.
> + *
> + * NOTE: Calls to ufs_get_page()/ufs_put_page() must be nested according to
> + * the rules documented in kmap_local_page()/kunmap_local().
> + *
> + * ufs_find_entry() and ufs_dotdot() act as calls to ufs_get_page() and
> + * must be treated accordingly for nesting purposes.
> + */
> +struct ufs_dir_entry *ufs_dotdot(struct inode *dir, struct page **p, void **pa)
> {
> - struct page *page = ufs_get_page(dir, 0);
> + void *page_addr;
> + struct page *page = ufs_get_page(dir, 0, &page_addr);
> struct ufs_dir_entry *de = NULL;
>
> if (!IS_ERR(page)) {
> de = ufs_next_entry(dir->i_sb,
> - (struct ufs_dir_entry *)page_address(page));
> + (struct ufs_dir_entry *)page_addr);
> *p = page;
> + *pa = page_addr;
> }
> return de;
> }
> @@ -246,9 +267,17 @@ struct ufs_dir_entry *ufs_dotdot(struct inode *dir, struct page **p)
> * returns the page in which the entry was found, and the entry itself
> * (as a parameter - res_dir). Page is returned mapped and unlocked.
> * Entry is guaranteed to be valid.
> + *
> + * On Success ufs_put_page() should be called on *res_page.
> + *
> + * NOTE: Calls to ufs_get_page()/ufs_put_page() must be nested according to
> + * the rules documented in kmap_local_page()/kunmap_local().
> + *
> + * ufs_find_entry() and ufs_dotdot() act as calls to ufs_get_page() and
> + * must be treated accordingly for nesting purposes.
> */
> struct ufs_dir_entry *ufs_find_entry(struct inode *dir, const struct qstr *qstr,
> - struct page **res_page)
> + struct page **res_page, void **res_page_addr)
> {
> struct super_block *sb = dir->i_sb;
> const unsigned char *name = qstr->name;
> @@ -259,6 +288,7 @@ struct ufs_dir_entry *ufs_find_entry(struct inode *dir, const struct qstr *qstr,
> struct page *page = NULL;
> struct ufs_inode_info *ui = UFS_I(dir);
> struct ufs_dir_entry *de;
> + void *page_addr;
>
> UFSD("ENTER, dir_ino %lu, name %s, namlen %u\n", dir->i_ino, name, namelen);
>
> @@ -267,6 +297,7 @@ struct ufs_dir_entry *ufs_find_entry(struct inode *dir, const struct qstr *qstr,
>
> /* OFFSET_CACHE */
> *res_page = NULL;
> + *res_page_addr = NULL;
>
> start = ui->i_dir_start_lookup;
>
> @@ -275,9 +306,10 @@ struct ufs_dir_entry *ufs_find_entry(struct inode *dir, const struct qstr *qstr,
> n = start;
> do {
> char *kaddr;
> - page = ufs_get_page(dir, n);
> +
> + page = ufs_get_page(dir, n, &page_addr);
> if (!IS_ERR(page)) {
> - kaddr = page_address(page);
> + kaddr = page_addr;
> de = (struct ufs_dir_entry *) kaddr;
> kaddr += ufs_last_byte(dir, n) - reclen;
> while ((char *) de <= kaddr) {
> @@ -285,7 +317,7 @@ struct ufs_dir_entry *ufs_find_entry(struct inode *dir, const struct qstr *qstr,
> goto found;
> de = ufs_next_entry(sb, de);
> }
> - ufs_put_page(page);
> + ufs_put_page(page, page_addr);
> }
> if (++n >= npages)
> n = 0;
> @@ -295,6 +327,7 @@ struct ufs_dir_entry *ufs_find_entry(struct inode *dir, const struct qstr *qstr,
>
> found:
> *res_page = page;
> + *res_page_addr = page_addr;
> ui->i_dir_start_lookup = n;
> return de;
> }
> @@ -312,6 +345,7 @@ int ufs_add_link(struct dentry *dentry, struct inode *inode)
> const unsigned int chunk_size = UFS_SB(sb)->s_uspi->s_dirblksize;
> unsigned short rec_len, name_len;
> struct page *page = NULL;
> + void *page_addr = NULL;
> struct ufs_dir_entry *de;
> unsigned long npages = dir_pages(dir);
> unsigned long n;
> @@ -329,12 +363,12 @@ int ufs_add_link(struct dentry *dentry, struct inode *inode)
> for (n = 0; n <= npages; n++) {
> char *dir_end;
>
> - page = ufs_get_page(dir, n);
> + page = ufs_get_page(dir, n, &page_addr);
> err = PTR_ERR(page);
> if (IS_ERR(page))
> goto out;
> lock_page(page);
> - kaddr = page_address(page);
> + kaddr = page_addr;
> dir_end = kaddr + ufs_last_byte(dir, n);
> de = (struct ufs_dir_entry *)kaddr;
> kaddr += PAGE_SIZE - reclen;
> @@ -365,14 +399,14 @@ int ufs_add_link(struct dentry *dentry, struct inode *inode)
> de = (struct ufs_dir_entry *) ((char *) de + rec_len);
> }
> unlock_page(page);
> - ufs_put_page(page);
> + ufs_put_page(page, page_addr);
> }
> BUG();
> return -EINVAL;
>
> got_it:
> pos = page_offset(page) +
> - (char*)de - (char*)page_address(page);
> + (char *)de - (char *)page_addr;
> err = ufs_prepare_chunk(page, pos, rec_len);
> if (err)
> goto out_unlock;
> @@ -396,7 +430,7 @@ int ufs_add_link(struct dentry *dentry, struct inode *inode)
> mark_inode_dirty(dir);
> /* OFFSET_CACHE */
> out_put:
> - ufs_put_page(page);
> + ufs_put_page(page, page_addr);
> out:
> return err;
> out_unlock:
> @@ -441,7 +475,7 @@ ufs_readdir(struct file *file, struct dir_context *ctx)
> char *kaddr, *limit;
> struct ufs_dir_entry *de;
>
> - struct page *page = ufs_get_page(inode, n);
> + struct page *page = ufs_get_page(inode, n, (void **)&kaddr);
>
> if (IS_ERR(page)) {
> ufs_error(sb, __func__,
> @@ -450,7 +484,6 @@ ufs_readdir(struct file *file, struct dir_context *ctx)
> ctx->pos += PAGE_SIZE - offset;
> return -EIO;
> }
> - kaddr = page_address(page);
> if (unlikely(need_revalidate)) {
> if (offset) {
> offset = ufs_validate_entry(sb, kaddr, offset, chunk_mask);
> @@ -476,13 +509,13 @@ ufs_readdir(struct file *file, struct dir_context *ctx)
> ufs_get_de_namlen(sb, de),
> fs32_to_cpu(sb, de->d_ino),
> d_type)) {
> - ufs_put_page(page);
> + ufs_put_page(page, kaddr);
> return 0;
> }
> }
> ctx->pos += fs16_to_cpu(sb, de->d_reclen);
> }
> - ufs_put_page(page);
> + ufs_put_page(page, kaddr);
> }
> return 0;
> }
> @@ -493,10 +526,9 @@ ufs_readdir(struct file *file, struct dir_context *ctx)
> * previous entry.
> */
> int ufs_delete_entry(struct inode *inode, struct ufs_dir_entry *dir,
> - struct page * page)
> + struct page *page, char *kaddr)
> {
> struct super_block *sb = inode->i_sb;
> - char *kaddr = page_address(page);
> unsigned from = ((char*)dir - kaddr) & ~(UFS_SB(sb)->s_uspi->s_dirblksize - 1);
> unsigned to = ((char*)dir - kaddr) + fs16_to_cpu(sb, dir->d_reclen);
> loff_t pos;
> @@ -522,7 +554,7 @@ int ufs_delete_entry(struct inode *inode, struct ufs_dir_entry *dir,
> de = ufs_next_entry(sb, de);
> }
> if (pde)
> - from = (char*)pde - (char*)page_address(page);
> + from = (char *)pde - kaddr;
>
> pos = page_offset(page) + from;
> lock_page(page);
> @@ -535,7 +567,7 @@ int ufs_delete_entry(struct inode *inode, struct ufs_dir_entry *dir,
> inode->i_ctime = inode->i_mtime = current_time(inode);
> mark_inode_dirty(inode);
> out:
> - ufs_put_page(page);
> + ufs_put_page(page, kaddr);
> UFSD("EXIT\n");
> return err;
> }
> @@ -559,8 +591,7 @@ int ufs_make_empty(struct inode * inode, struct inode *dir)
> goto fail;
> }
>
> - kmap(page);
> - base = (char*)page_address(page);
> + base = kmap_local_page(page);
> memset(base, 0, PAGE_SIZE);
>
> de = (struct ufs_dir_entry *) base;
> @@ -577,7 +608,7 @@ int ufs_make_empty(struct inode * inode, struct inode *dir)
> de->d_reclen = cpu_to_fs16(sb, chunk_size - UFS_DIR_REC_LEN(1));
> ufs_set_de_namlen(sb, de, 2);
> strcpy (de->d_name, "..");
> - kunmap(page);
> + kunmap_local(base);
>
> err = ufs_commit_chunk(page, 0, chunk_size);
> fail:
> @@ -592,17 +623,18 @@ int ufs_empty_dir(struct inode * inode)
> {
> struct super_block *sb = inode->i_sb;
> struct page *page = NULL;
> + void *page_addr;
> unsigned long i, npages = dir_pages(inode);
>
> for (i = 0; i < npages; i++) {
> char *kaddr;
> struct ufs_dir_entry *de;
> - page = ufs_get_page(inode, i);
>
> + page = ufs_get_page(inode, i, &page_addr);
> if (IS_ERR(page))
> continue;
>
> - kaddr = page_address(page);
> + kaddr = page_addr;
> de = (struct ufs_dir_entry *)kaddr;
> kaddr += ufs_last_byte(inode, i) - UFS_DIR_REC_LEN(1);
>
> @@ -629,12 +661,12 @@ int ufs_empty_dir(struct inode * inode)
> }
> de = ufs_next_entry(sb, de);
> }
> - ufs_put_page(page);
> + ufs_put_page(page, page_addr);
> }
> return 1;
>
> not_empty:
> - ufs_put_page(page);
> + ufs_put_page(page, page_addr);
> return 0;
> }
>
> diff --git a/fs/ufs/namei.c b/fs/ufs/namei.c
> index 29d5a0e0c8f0..cdf3bcf9d02e 100644
> --- a/fs/ufs/namei.c
> +++ b/fs/ufs/namei.c
> @@ -210,13 +210,14 @@ static int ufs_unlink(struct inode *dir, struct dentry *dentry)
> struct inode * inode = d_inode(dentry);
> struct ufs_dir_entry *de;
> struct page *page;
> + void *page_addr;
> int err = -ENOENT;
>
> - de = ufs_find_entry(dir, &dentry->d_name, &page);
> + de = ufs_find_entry(dir, &dentry->d_name, &page, &page_addr);
> if (!de)
> goto out;
>
> - err = ufs_delete_entry(dir, de, page);
> + err = ufs_delete_entry(dir, de, page, page_addr);
> if (err)
> goto out;
>
> @@ -250,27 +251,31 @@ static int ufs_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
> struct inode *old_inode = d_inode(old_dentry);
> struct inode *new_inode = d_inode(new_dentry);
> struct page *dir_page = NULL;
> + void *dir_page_addr;
> struct ufs_dir_entry * dir_de = NULL;
> struct page *old_page;
> + void *old_page_addr;
> struct ufs_dir_entry *old_de;
> int err = -ENOENT;
>
> if (flags & ~RENAME_NOREPLACE)
> return -EINVAL;
>
> - old_de = ufs_find_entry(old_dir, &old_dentry->d_name, &old_page);
> + old_de = ufs_find_entry(old_dir, &old_dentry->d_name, &old_page,
> + &old_page_addr);
> if (!old_de)
> goto out;
>
> if (S_ISDIR(old_inode->i_mode)) {
> err = -EIO;
> - dir_de = ufs_dotdot(old_inode, &dir_page);
> + dir_de = ufs_dotdot(old_inode, &dir_page, &dir_page_addr);
> if (!dir_de)
> goto out_old;
> }
>
> if (new_inode) {
> struct page *new_page;
> + void *new_page_addr;
> struct ufs_dir_entry *new_de;
>
> err = -ENOTEMPTY;
> @@ -278,10 +283,11 @@ static int ufs_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
> goto out_dir;
>
> err = -ENOENT;
> - new_de = ufs_find_entry(new_dir, &new_dentry->d_name, &new_page);
> + new_de = ufs_find_entry(new_dir, &new_dentry->d_name, &new_page,
> + &new_page_addr);
> if (!new_de)
> goto out_dir;
> - ufs_set_link(new_dir, new_de, new_page, old_inode, 1);
> + ufs_set_link(new_dir, new_de, new_page, new_page_addr, old_inode, 1);
> new_inode->i_ctime = current_time(new_inode);
> if (dir_de)
> drop_nlink(new_inode);
> @@ -300,29 +306,25 @@ static int ufs_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
> */
> old_inode->i_ctime = current_time(old_inode);
>
> - ufs_delete_entry(old_dir, old_de, old_page);
> + ufs_delete_entry(old_dir, old_de, old_page, old_page_addr);
> mark_inode_dirty(old_inode);
>
> if (dir_de) {
> if (old_dir != new_dir)
> - ufs_set_link(old_inode, dir_de, dir_page, new_dir, 0);
> - else {
> - kunmap(dir_page);
> - put_page(dir_page);
> - }
> + ufs_set_link(old_inode, dir_de, dir_page,
> + dir_page_addr, new_dir, 0);
> + else
> + ufs_put_page(dir_page, dir_page_addr);
> inode_dec_link_count(old_dir);
> }
> return 0;
>
>
> out_dir:
> - if (dir_de) {
> - kunmap(dir_page);
> - put_page(dir_page);
> - }
> + if (dir_de)
> + ufs_put_page(dir_page, dir_page_addr);
> out_old:
> - kunmap(old_page);
> - put_page(old_page);
> + ufs_put_page(old_page, old_page_addr);
> out:
> return err;
> }
> diff --git a/fs/ufs/ufs.h b/fs/ufs/ufs.h
> index 550f7c5a3636..20d224c163ab 100644
> --- a/fs/ufs/ufs.h
> +++ b/fs/ufs/ufs.h
> @@ -102,12 +102,16 @@ extern const struct inode_operations ufs_dir_inode_operations;
> extern int ufs_add_link (struct dentry *, struct inode *);
> extern ino_t ufs_inode_by_name(struct inode *, const struct qstr *);
> extern int ufs_make_empty(struct inode *, struct inode *);
> -extern struct ufs_dir_entry *ufs_find_entry(struct inode *, const struct qstr *, struct page **);
> -extern int ufs_delete_entry(struct inode *, struct ufs_dir_entry *, struct page *);
> +extern struct ufs_dir_entry *ufs_find_entry(struct inode *dir, const struct qstr *qstr,
> + struct page **res_page, void **res_page_addr);
> +extern int ufs_delete_entry(struct inode *inode, struct ufs_dir_entry *dir,
> + struct page *page, char *kaddr);
> extern int ufs_empty_dir (struct inode *);
> -extern struct ufs_dir_entry *ufs_dotdot(struct inode *, struct page **);
> +extern struct ufs_dir_entry *ufs_dotdot(struct inode *dir, struct page **p, void **pa);
> extern void ufs_set_link(struct inode *dir, struct ufs_dir_entry *de,
> - struct page *page, struct inode *inode, bool update_times);
> + struct page *page, void *page_addr,
> + struct inode *inode, bool update_times);
> +extern void ufs_put_page(struct page *page, void *page_addr);
>
> /* file.c */
> extern const struct inode_operations ufs_file_inode_operations;
> --
> 2.37.1
>