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authorAl Viro <viro@zeniv.linux.org.uk>2016-04-15 00:58:55 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2016-05-02 19:49:26 -0400
commit84e710da2a1dfacfc87f604869a4d22df91ce6cd (patch)
tree37625d5ef48c43a17c6da2f5a80b107da5524957 /fs/inode.c
parent85c7f81041d57cfe9dc97f4680d5586b54534a39 (diff)
downloadop-kernel-dev-84e710da2a1dfacfc87f604869a4d22df91ce6cd.zip
op-kernel-dev-84e710da2a1dfacfc87f604869a4d22df91ce6cd.tar.gz
parallel lookups machinery, part 2
We'll need to verify that there's neither a hashed nor in-lookup dentry with desired parent/name before adding to in-lookup set. One possible solution would be to hold the parent's ->d_lock through both checks, but while the in-lookup set is relatively small at any time, dcache is not. And holding the parent's ->d_lock through something like __d_lookup_rcu() would suck too badly. So we leave the parent's ->d_lock alone, which means that we watch out for the following scenario: * we verify that there's no hashed match * existing in-lookup match gets hashed by another process * we verify that there's no in-lookup matches and decide that everything's fine. Solution: per-directory kinda-sorta seqlock, bumped around the times we hash something that used to be in-lookup or move (and hash) something in place of in-lookup. Then the above would turn into * read the counter * do dcache lookup * if no matches found, check for in-lookup matches * if there had been none of those either, check if the counter has changed; repeat if it has. The "kinda-sorta" part is due to the fact that we don't have much spare space in inode. There is a spare word (shared with i_bdev/i_cdev/i_pipe), so the counter part is not a problem, but spinlock is a different story. We could use the parent's ->d_lock, and it would be less painful in terms of contention, for __d_add() it would be rather inconvenient to grab; we could do that (using lock_parent()), but... Fortunately, we can get serialization on the counter itself, and it might be a good idea in general; we can use cmpxchg() in a loop to get from even to odd and smp_store_release() from odd to even. This commit adds the counter and updating logics; the readers will be added in the next commit. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/inode.c')
-rw-r--r--fs/inode.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/fs/inode.c b/fs/inode.c
index 4202aac..4b884f7 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -151,6 +151,7 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
inode->i_bdev = NULL;
inode->i_cdev = NULL;
inode->i_link = NULL;
+ inode->i_dir_seq = 0;
inode->i_rdev = 0;
inode->dirtied_when = 0;
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