From 37c42524d6090644206ae6d310d7e830bd3ccb47 Mon Sep 17 00:00:00 2001 From: "Denis V. Lunev" Date: Tue, 16 Oct 2007 23:29:53 -0700 Subject: [PATCH] shrink_dcache_sb speedup This patch makes shrink_dcache_sb consistent with dentry pruning policy. On the first pass we iterate over dentry unused list and prepare some dentries for removal. However, since the existing code moves evicted dentries to the beginning of the LRU it can happen that fresh dentries from other superblocks will be inserted *before* our dentries. This can result in significant slowdown of shrink_dcache_sb(). Moreover, for virtual filesystems like unionfs which can call dput() during dentries kill existing code results in O(n^2) complexity. We observed 2 minutes shrink_dcache_sb() with only 35000 dentries. To avoid this effects we propose to isolate sb dentries at the end of LRU list. Signed-off-by: Denis V. Lunev Signed-off-by: Kirill Korotaev Signed-off-by: Andrey Mirkin Cc: Neil Brown Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/dcache.c | 6 +++--- include/linux/list.h | 12 ++++++++++++ 2 files changed, 15 insertions(+), 3 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index 5cdd14e958..42d290be0a 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -553,18 +553,18 @@ void shrink_dcache_sb(struct super_block * sb) * superblock to the most recent end of the unused list. */ spin_lock(&dcache_lock); - list_for_each_safe(tmp, next, &dentry_unused) { + list_for_each_prev_safe(tmp, next, &dentry_unused) { dentry = list_entry(tmp, struct dentry, d_lru); if (dentry->d_sb != sb) continue; - list_move(tmp, &dentry_unused); + list_move_tail(tmp, &dentry_unused); } /* * Pass two ... free the dentries for this superblock. */ repeat: - list_for_each_safe(tmp, next, &dentry_unused) { + list_for_each_prev_safe(tmp, next, &dentry_unused) { dentry = list_entry(tmp, struct dentry, d_lru); if (dentry->d_sb != sb) continue; diff --git a/include/linux/list.h b/include/linux/list.h index ad9dcb9e33..b0cf0135fe 100644 --- a/include/linux/list.h +++ b/include/linux/list.h @@ -477,6 +477,18 @@ static inline void list_splice_init_rcu(struct list_head *list, for (pos = (head)->next, n = pos->next; pos != (head); \ pos = n, n = pos->next) +/** + * list_for_each_prev_safe - iterate over a list backwards safe against removal + of list entry + * @pos: the &struct list_head to use as a loop cursor. + * @n: another &struct list_head to use as temporary storage + * @head: the head for your list. + */ +#define list_for_each_prev_safe(pos, n, head) \ + for (pos = (head)->prev, n = pos->prev; \ + prefetch(pos->prev), pos != (head); \ + pos = n, n = pos->prev) + /** * list_for_each_entry - iterate over list of given type * @pos: the type * to use as a loop cursor. -- 2.39.5