kmap() is 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.
kmap_local_page() in fs/sysv does not violate any of the strict rules of
its use, therefore it should be preferred.
Therefore, replace kmap() with kmap_local_page() in fs/sysv. kunmap_local()
requires the mapping address, so return that address from dir_get_page()
to be used in dir_put_page().
I had submitted a patch with the same purpose but it has been replaced
by this series.[1] This is based on a long series of very appreciated
comments and suggestions kindly provided by Al Viro (again thanks!).[2][3][4]
Since this is a very different thing, versioning restarts from scratch.
[1] https://lore.kernel.org/lkml/[email protected]/
[2] https://lore.kernel.org/lkml/Y4E++JERgUMoqfjG@ZenIV/#t
[3] https://lore.kernel.org/lkml/Y4FG0O7VWTTng5yh@ZenIV/#t
[4] https://lore.kernel.org/lkml/Y4ONIFJatIGsVNpf@ZenIV/#t
Cc: Al Viro <[email protected]>
Cc: Ira Weiny <[email protected]>
Signed-off-by: Fabio M. De Francesco <[email protected]>
Fabio M. De Francesco (4):
fs/sysv: Use the offset_in_page() helper
fs/sysv: Change the signature of dir_get_page()
fs/sysv: Use dir_put_page() in sysv_rename()
fs/sysv: Replace kmap() with kmap_local_page()
fs/sysv/dir.c | 117 +++++++++++++++++++++++++++---------------------
fs/sysv/namei.c | 9 ++--
fs/sysv/sysv.h | 1 +
3 files changed, 71 insertions(+), 56 deletions(-)
--
2.39.0
Use the offset_in_page() helper because it is more suitable than doing
explicit subtractions between pointers to directory entries and kernel
virtual addresses of mapped pages.
Cc: Ira Weiny <[email protected]>
Suggested-by: Al Viro <[email protected]>
Signed-off-by: Fabio M. De Francesco <[email protected]>
---
fs/sysv/dir.c | 9 +++------
1 file changed, 3 insertions(+), 6 deletions(-)
diff --git a/fs/sysv/dir.c b/fs/sysv/dir.c
index 88e38cd8f5c9..685379bc9d64 100644
--- a/fs/sysv/dir.c
+++ b/fs/sysv/dir.c
@@ -206,8 +206,7 @@ int sysv_add_link(struct dentry *dentry, struct inode *inode)
return -EINVAL;
got_it:
- pos = page_offset(page) +
- (char*)de - (char*)page_address(page);
+ pos = page_offset(page) + offset_in_page(de);
lock_page(page);
err = sysv_prepare_chunk(page, pos, SYSV_DIRSIZE);
if (err)
@@ -230,8 +229,7 @@ int sysv_add_link(struct dentry *dentry, struct inode *inode)
int sysv_delete_entry(struct sysv_dir_entry *de, struct page *page)
{
struct inode *inode = page->mapping->host;
- char *kaddr = (char*)page_address(page);
- loff_t pos = page_offset(page) + (char *)de - kaddr;
+ loff_t pos = page_offset(page) + offset_in_page(de);
int err;
lock_page(page);
@@ -328,8 +326,7 @@ void sysv_set_link(struct sysv_dir_entry *de, struct page *page,
struct inode *inode)
{
struct inode *dir = page->mapping->host;
- loff_t pos = page_offset(page) +
- (char *)de-(char*)page_address(page);
+ loff_t pos = page_offset(page) + offset_in_page(de);
int err;
lock_page(page);
--
2.39.0
Use the dir_put_page() helper in sysv_rename() instead of open-coding two
kunmap() + put_page().
Cc: Al Viro <[email protected]>
Suggested-by: Ira Weiny <[email protected]>
Signed-off-by: Fabio M. De Francesco <[email protected]>
---
fs/sysv/dir.c | 2 +-
fs/sysv/namei.c | 9 +++------
fs/sysv/sysv.h | 1 +
3 files changed, 5 insertions(+), 7 deletions(-)
diff --git a/fs/sysv/dir.c b/fs/sysv/dir.c
index 0a8b5828c390..a37747e9e9a3 100644
--- a/fs/sysv/dir.c
+++ b/fs/sysv/dir.c
@@ -28,7 +28,7 @@ const struct file_operations sysv_dir_operations = {
.fsync = generic_file_fsync,
};
-static inline void dir_put_page(struct page *page)
+inline void dir_put_page(struct page *page)
{
kunmap(page);
put_page(page);
diff --git a/fs/sysv/namei.c b/fs/sysv/namei.c
index b2e6abc06a2d..981c1d76f342 100644
--- a/fs/sysv/namei.c
+++ b/fs/sysv/namei.c
@@ -250,13 +250,10 @@ static int sysv_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
return 0;
out_dir:
- if (dir_de) {
- kunmap(dir_page);
- put_page(dir_page);
- }
+ if (dir_de)
+ dir_put_page(dir_page);
out_old:
- kunmap(old_page);
- put_page(old_page);
+ dir_put_page(old_page);
out:
return err;
}
diff --git a/fs/sysv/sysv.h b/fs/sysv/sysv.h
index 99ddf033da4f..b250ac1dd348 100644
--- a/fs/sysv/sysv.h
+++ b/fs/sysv/sysv.h
@@ -148,6 +148,7 @@ extern void sysv_destroy_icache(void);
/* dir.c */
+extern void dir_put_page(struct page *page);
extern struct sysv_dir_entry *sysv_find_entry(struct dentry *, struct page **);
extern int sysv_add_link(struct dentry *, struct inode *);
extern int sysv_delete_entry(struct sysv_dir_entry *, struct page *);
--
2.39.0