linux-kernel - [PATCH V11 10/11] fs: Introduce DCACHE

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Date:   Mon, 27 Apr 2020 17:21:41 -0700
From:   ira.weiny@...el.com
To:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     Ira Weiny <ira.weiny@...el.com>, Al Viro <viro@...iv.linux.org.uk>,
        Jan Kara <jack@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jeff Moyer <jmoyer@...hat.com>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org
Subject: [PATCH V11 10/11] fs: Introduce DCACHE_DONTCACHE

From: Ira Weiny <ira.weiny@...el.com>

DCACHE_DONTCACHE indicates a dentry should not be cached on final
dput().

Also add a helper function to mark DCACHE_DONTCACHE on all dentries
pointing to a specific inode when that inode is being set I_DONTCACHE.

This facilitates dropping dentry references to inodes sooner which
require eviction to swap S_DAX mode.

Cc: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Ira Weiny <ira.weiny@...el.com>

---
Changes from V10:
	rename to d_mark_dontcache()
	Move function to fs/dcache.c

Changes from V9:
	modify i_state under i_lock
	Update comment
		"Purge from memory on final dput()"

Changes from V8:
	Update commit message
	Use mark_inode_dontcache in XFS
	Fix locking...  can't use rcu here.
	Change name to mark_inode_dontcache
---
 fs/dcache.c            | 19 +++++++++++++++++++
 fs/xfs/xfs_icache.c    |  2 +-
 include/linux/dcache.h |  2 ++
 include/linux/fs.h     |  1 +
 4 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index b280e07e162b..0d07fb335b78 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -647,6 +647,10 @@ static inline bool retain_dentry(struct dentry *dentry)
 		if (dentry->d_op->d_delete(dentry))
 			return false;
 	}
+
+	if (unlikely(dentry->d_flags & DCACHE_DONTCACHE))
+		return false;
+
 	/* retain; LRU fodder */
 	dentry->d_lockref.count--;
 	if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST)))
@@ -656,6 +660,21 @@ static inline bool retain_dentry(struct dentry *dentry)
 	return true;
 }
 
+void d_mark_dontcache(struct inode *inode)
+{
+	struct dentry *de;
+
+	spin_lock(&inode->i_lock);
+	hlist_for_each_entry(de, &inode->i_dentry, d_u.d_alias) {
+		spin_lock(&de->d_lock);
+		de->d_flags |= DCACHE_DONTCACHE;
+		spin_unlock(&de->d_lock);
+	}
+	inode->i_state |= I_DONTCACHE;
+	spin_unlock(&inode->i_lock);
+}
+EXPORT_SYMBOL(d_mark_dontcache);
+
 /*
  * Finish off a dentry we've decided to kill.
  * dentry->d_lock must be held, returns with it unlocked.
diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c
index de76f7f60695..888646d74d7d 100644
--- a/fs/xfs/xfs_icache.c
+++ b/fs/xfs/xfs_icache.c
@@ -559,7 +559,7 @@ xfs_iget_cache_miss(
 	 */
 	iflags = XFS_INEW;
 	if (flags & XFS_IGET_DONTCACHE)
-		VFS_I(ip)->i_state |= I_DONTCACHE;
+		d_mark_dontcache(VFS_I(ip));
 	ip->i_udquot = NULL;
 	ip->i_gdquot = NULL;
 	ip->i_pdquot = NULL;
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index c1488cc84fd9..a81f0c3cf352 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -177,6 +177,8 @@ struct dentry_operations {
 
 #define DCACHE_REFERENCED		0x00000040 /* Recently used, don't discard. */
 
+#define DCACHE_DONTCACHE		0x00000080 /* Purge from memory on final dput() */
+
 #define DCACHE_CANT_MOUNT		0x00000100
 #define DCACHE_GENOCIDE			0x00000200
 #define DCACHE_SHRINK_LIST		0x00000400
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 44bd45af760f..7c3e8c0306e0 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3055,6 +3055,7 @@ static inline int generic_drop_inode(struct inode *inode)
 	return !inode->i_nlink || inode_unhashed(inode) ||
 		(inode->i_state & I_DONTCACHE);
 }
+extern void d_mark_dontcache(struct inode *inode);
 
 extern struct inode *ilookup5_nowait(struct super_block *sb,
 		unsigned long hashval, int (*test)(struct inode *, void *),
-- 
2.25.1