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SubjectRe: [PATCH v3 3/3] fs/ufs: Replace kmap() with kmap_local_page()
Date
On sabato 17 dicembre 2022 19:47:49 CET 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().
>
> Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
> Suggested-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> ---
> fs/ufs/dir.c | 75 ++++++++++++++++++++++++++++++++--------------------
> 1 file changed, 46 insertions(+), 29 deletions(-)
>
> diff --git a/fs/ufs/dir.c b/fs/ufs/dir.c
> index 9fa86614d2d1..a9dd5023b604 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)
> +static inline void ufs_put_page(struct page *page, void *page_addr)
> {
> - kunmap(page);
> + kunmap((void *)((unsigned long)page_addr & PAGE_MASK));

While working on patch 3/3 of a similar series for fs/sysv a few minutes ago,
I noticed this call to kunmap() instead of kunmap_local().

I will wait a day or two before sending the next version, to leave additional
time for those who want to comment / review.

Fabio

> put_page(page);
> }
>
> @@ -76,7 +76,7 @@ ino_t ufs_inode_by_name(struct inode *dir, const struct
qstr
> *qstr) de = ufs_find_entry(dir, qstr, &page);
> if (de) {
> res = fs32_to_cpu(dir->i_sb, de->d_ino);
> - ufs_put_page(page);
> + ufs_put_page(page, de);
> }
> return res;
> }
> @@ -99,18 +99,17 @@ 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, de);
> 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;
> @@ -185,23 +184,32 @@ static bool ufs_check_page(struct page *page)
> return false;
> }
>
> +/*
> + * 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 void *ufs_get_page(struct inode *dir, unsigned long n, struct page
> **p) {
> + char *kaddr;
> +
> struct address_space *mapping = dir->i_mapping;
> struct page *page = read_mapping_page(mapping, n, NULL);
> if (!IS_ERR(page)) {
> - kmap(page);
> + kaddr = kmap_local_page(page);
> if (unlikely(!PageChecked(page))) {
> - if (!ufs_check_page(page))
> + if (!ufs_check_page(page, kaddr))
> goto fail;
> }
> *p = page;
> - return page_address(page);
> + return kaddr;
> }
> return ERR_CAST(page);
>
> fail:
> - ufs_put_page(page);
> + ufs_put_page(page, kaddr);
> return ERR_PTR(-EIO);
> }
>
> @@ -227,6 +235,13 @@ ufs_next_entry(struct super_block *sb, struct
> ufs_dir_entry *p) fs16_to_cpu(sb, p->d_reclen));
> }
>
> +/*
> + * Calls to ufs_get_page()/ufs_put_page() must be nested according to the
> + * rules documented in kmap_local_page()/kunmap_local().
> + *
> + * ufs_dotdot() acts as a call to ufs_get_page() and must be treated
> + * accordingly for nesting purposes.
> + */
> struct ufs_dir_entry *ufs_dotdot(struct inode *dir, struct page **p)
> {
> struct ufs_dir_entry *de = ufs_get_page(dir, 0, p);
> @@ -238,12 +253,15 @@ struct ufs_dir_entry *ufs_dotdot(struct inode *dir,
> struct page **p) }
>
> /*
> - * ufs_find_entry()
> + * Finds an entry in the specified directory with the wanted name. It
returns
> a + * pointer to the directory's entry. The page in which the entry was
found
> is + * in the res_page out parameter. The page is returned mapped and
> unlocked. + * The entry is guaranteed to be valid.
> *
> - * finds an entry in the specified directory with the wanted name. It
> - * 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.
> + *
> + * ufs_find_entry() acts as a call 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)
> @@ -282,7 +300,7 @@ 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, kaddr);
> }
> if (++n >= npages)
> n = 0;
> @@ -360,7 +378,7 @@ 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, kaddr);
> }
> BUG();
> return -EINVAL;
> @@ -390,7 +408,7 @@ 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, kaddr);
> return err;
> out_unlock:
> unlock_page(page);
> @@ -468,13 +486,13 @@ 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;
> }
> @@ -485,10 +503,10 @@ 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)
> {
> struct super_block *sb = inode->i_sb;
> - char *kaddr = page_address(page);
> + char *kaddr = (char *)((unsigned long)dir & PAGE_MASK);
> unsigned int from = offset_in_page(dir) & ~(UFS_SB(sb)->s_uspi-
>s_dirblksize
> - 1); unsigned int to = offset_in_page(dir) + fs16_to_cpu(sb, dir-
>d_reclen);
> loff_t pos;
> @@ -527,7 +545,7 @@ 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;
> }
> @@ -551,8 +569,7 @@ 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;
> @@ -569,7 +586,7 @@ 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:
> @@ -585,9 +602,9 @@ int ufs_empty_dir(struct inode * inode)
> struct super_block *sb = inode->i_sb;
> struct page *page = NULL;
> unsigned long i, npages = dir_pages(inode);
> + char *kaddr;
>
> for (i = 0; i < npages; i++) {
> - char *kaddr;
> struct ufs_dir_entry *de;
>
> kaddr = ufs_get_page(inode, i, &page);
> @@ -620,12 +637,12 @@ int ufs_empty_dir(struct inode * inode)
> }
> de = ufs_next_entry(sb, de);
> }
> - ufs_put_page(page);
> + ufs_put_page(page, kaddr);
> }
> return 1;
>
> not_empty:
> - ufs_put_page(page);
> + ufs_put_page(page, kaddr);
> return 0;
> }
>
> --
> 2.39.0




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