It looks from profiles like ext4_getattr() is fairly expensive,
because it unnecessarily accesses the extended inode information and
causes extra cache misses.
On an empty kernel allmodconfig build (which is a lot of "stat()"
calls by Make, and a lot of silly string stuff in user space due to
all the make variable games we play), ext4_getattr() was something
like 1% of the time according to the profile I gathered. It might be
bogus - maybe the cacheline ends up being accessed later anyway, but
it _looked_ like it was the whole "i_extra_isize" access that missed
in the cache.
That's all for gathering the STATX_BTIME information, that the caller
doesn't even *want*.
How about a patch like the attached?
Linus
fs/ext4/inode.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 516faa280ced..617dc8835f5f 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5700,7 +5700,7 @@ int ext4_getattr(const struct path *path, struct kstat *stat,
struct ext4_inode_info *ei = EXT4_I(inode);
unsigned int flags;
- if (EXT4_FITS_IN_INODE(raw_inode, ei, i_crtime)) {
+ if ((query_flags & STATX_BTIME) && EXT4_FITS_IN_INODE(raw_inode, ei, i_crtime)) {
stat->result_mask |= STATX_BTIME;
stat->btime.tv_sec = ei->i_crtime.tv_sec;
stat->btime.tv_nsec = ei->i_crtime.tv_nsec;
