From: Hao Li <lihao2018.fnst@cn.fujitsu.com>
To: <linux-kernel@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>
Cc: <david@fromorbit.com>, <ira.weiny@intel.com>,
<linux-xfs@vger.kernel.org>, <viro@zeniv.linux.org.uk>,
<y-goto@fujitsu.com>, <lihao2018.fnst@cn.fujitsu.com>
Subject: [PATCH v2] fs: Kill DCACHE_DONTCACHE dentry even if DCACHE_REFERENCED is set
Date: Thu, 24 Sep 2020 13:59:58 +0800 [thread overview]
Message-ID: <20200924055958.825515-1-lihao2018.fnst@cn.fujitsu.com> (raw)
If DCACHE_REFERENCED is set, fast_dput() will return true, and then
retain_dentry() have no chance to check DCACHE_DONTCACHE. As a result,
the dentry won't be killed and the corresponding inode can't be evicted.
In the following example, the DAX policy can't take effects unless we
do a drop_caches manually.
# DCACHE_LRU_LIST will be set
echo abcdefg > test.txt
# DCACHE_REFERENCED will be set and DCACHE_DONTCACHE can't do anything
xfs_io -c 'chattr +x' test.txt
# Drop caches to make DAX changing take effects
echo 2 > /proc/sys/vm/drop_caches
What this patch does is preventing fast_dput() from returning true if
DCACHE_DONTCACHE is set. Then retain_dentry() will detect the
DCACHE_DONTCACHE and will return false. As a result, the dentry will be
killed and the inode will be evicted. In this way, if we change per-file
DAX policy, it will take effects automatically after this file is closed
by all processes.
I also add some comments to make the code more clear.
Signed-off-by: Hao Li <lihao2018.fnst@cn.fujitsu.com>
---
v1 is split into two standalone patch as discussed in [1], and the first
patch has been reviewed in [2]. This is the second patch.
[1]: https://lore.kernel.org/linux-fsdevel/20200831003407.GE12096@dread.disaster.area/
[2]: https://lore.kernel.org/linux-fsdevel/20200906214002.GI12131@dread.disaster.area/
fs/dcache.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index ea0485861d93..97e81a844a96 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -793,10 +793,17 @@ static inline bool fast_dput(struct dentry *dentry)
* a reference to the dentry and change that, but
* our work is done - we can leave the dentry
* around with a zero refcount.
+ *
+ * Nevertheless, there are two cases that we should kill
+ * the dentry anyway.
+ * 1. free disconnected dentries as soon as their refcount
+ * reached zero.
+ * 2. free dentries if they should not be cached.
*/
smp_rmb();
d_flags = READ_ONCE(dentry->d_flags);
- d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED;
+ d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST |
+ DCACHE_DISCONNECTED | DCACHE_DONTCACHE;
/* Nothing to do? Dropping the reference was all we needed? */
if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry))
--
2.28.0
next reply other threads:[~2020-09-24 6:00 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-24 5:59 Hao Li [this message]
2020-09-24 14:58 ` [PATCH v2] fs: Kill DCACHE_DONTCACHE dentry even if DCACHE_REFERENCED is set Jan Kara
2020-10-21 13:51 ` Jan Kara
2020-11-05 10:54 ` Li, Hao
2020-09-24 15:27 ` Ira Weiny
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