From: Hao Li <email@example.com> To: <firstname.lastname@example.org>, <email@example.com> Cc: <firstname.lastname@example.org>, <email@example.com>, <firstname.lastname@example.org>, <email@example.com>, <firstname.lastname@example.org>, <email@example.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: <firstname.lastname@example.org> (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 <email@example.com> --- v1 is split into two standalone patch as discussed in , and the first patch has been reviewed in . This is the second patch. : https://lore.kernel.org/linux-fsdevel/20200831003407.GE12096@dread.disaster.area/ : 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 ` 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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