From 4a4be1ad3a6efea16c56615f31117590fd881358 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Wed, 29 May 2024 09:39:34 -0700 Subject: [PATCH] Revert "vfs: Delete the associated dentry when deleting a file" This reverts commit 681ce8623567ba7e7333908e9826b77145312dda. We gave it a try, but it turns out the kernel test robot did in fact find performance regressions for it, so we'll have to look at the more involved alternative fixes for Yafang Shao's Elasticsearch load issue. There were several alternatives discussed, they just weren't as simple as this first attempt. The report is of a -7.4% regression of filebench.sum_operations/s, which appears significant enough to trigger my "this patch may get reverted if somebody finds a performance regression on some other load" rule. So it's still the case that we should end up deleting dentries more aggressively - or just be better at pruning them later - but it needs a bit more finesse than this simple thing. Link: https://lore.kernel.org/all/202405291318.4dfbb352-oliver.sang@intel.com/ Cc: Yafang Shao Cc: Al Viro Cc: Christian Brauner Signed-off-by: Linus Torvalds --- fs/dcache.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index 1ee6404b430b..407095188f83 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2360,17 +2360,19 @@ EXPORT_SYMBOL(d_hash_and_lookup); * - unhash this dentry and free it. * * Usually, we want to just turn this into - * a negative dentry, but certain workloads can - * generate a large number of negative dentries. - * Therefore, it would be better to simply - * unhash it. + * a negative dentry, but if anybody else is + * currently using the dentry or the inode + * we can't do that and we fall back on removing + * it from the hash queues and waiting for + * it to be deleted later when it has no users */ /** * d_delete - delete a dentry * @dentry: The dentry to delete * - * Remove the dentry from the hash queues so it can be deleted later. + * Turn the dentry into a negative dentry if possible, otherwise + * remove it from the hash queues so it can be deleted later */ void d_delete(struct dentry * dentry) @@ -2379,8 +2381,6 @@ void d_delete(struct dentry * dentry) spin_lock(&inode->i_lock); spin_lock(&dentry->d_lock); - __d_drop(dentry); - /* * Are we the only user? */ @@ -2388,6 +2388,7 @@ void d_delete(struct dentry * dentry) dentry->d_flags &= ~DCACHE_CANT_MOUNT; dentry_unlink_inode(dentry); } else { + __d_drop(dentry); spin_unlock(&dentry->d_lock); spin_unlock(&inode->i_lock); }