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Subject[PATCH] fs: optimise generic_write_check_limits()
Date
Even though ->s_maxbytes is used by generic_write_check_limits() only in
case of O_LARGEFILE, the value is loaded unconditionally, which is heavy
and takes 4 indirect loads. Optimise it by not touching ->s_maxbytes,
if it's not going to be used.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
fs/read_write.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 9db7adf160d2..db662d0c3cfa 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1609,9 +1609,8 @@ SYSCALL_DEFINE6(copy_file_range, int, fd_in, loff_t __user *, off_in,
*/
int generic_write_check_limits(struct file *file, loff_t pos, loff_t *count)
{
- struct inode *inode = file->f_mapping->host;
- loff_t max_size = inode->i_sb->s_maxbytes;
loff_t limit = rlimit(RLIMIT_FSIZE);
+ loff_t max_size = MAX_NON_LFS;

if (limit != RLIM_INFINITY) {
if (pos >= limit) {
@@ -1621,8 +1620,11 @@ int generic_write_check_limits(struct file *file, loff_t pos, loff_t *count)
*count = min(*count, limit - pos);
}

- if (!(file->f_flags & O_LARGEFILE))
- max_size = MAX_NON_LFS;
+ if (file->f_flags & O_LARGEFILE) {
+ struct inode *inode = file->f_mapping->host;
+
+ max_size = inode->i_sb->s_maxbytes;
+ }

if (unlikely(pos >= max_size))
return -EFBIG;
--
2.32.0
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