linux-kernel - [PATCH 55/67] afs: Skip truncation on the server of data we haven't written yet

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Message-ID: <163456951186.2614702.16840420880926305225.stgit@warthog.procyon.org.uk>
Date:   Mon, 18 Oct 2021 16:05:11 +0100
From:   David Howells <dhowells@...hat.com>
To:     linux-cachefs@...hat.com
Cc:     dhowells@...hat.com, Trond Myklebust <trondmy@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Jeff Layton <jlayton@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Omar Sandoval <osandov@...ndov.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-afs@...ts.infradead.org, linux-nfs@...r.kernel.org,
        linux-cifs@...r.kernel.org, ceph-devel@...r.kernel.org,
        v9fs-developer@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 55/67] afs: Skip truncation on the server of data we haven't
 written yet

Don't send a truncation RPC to the server if we're only shortening data
that's in the pagecache and is beyond the server's EOF.

Also don't automatically force writeback on setattr, but do wait to store
RPCs that are in the region to be removed on a shortening truncation.

Signed-off-by: David Howells <dhowells@...hat.com>
---

 fs/afs/inode.c |   45 +++++++++++++++++++++++++++++++++++----------
 1 file changed, 35 insertions(+), 10 deletions(-)

diff --git a/fs/afs/inode.c b/fs/afs/inode.c
index c4af4fda37dd..4c66a2b86add 100644
--- a/fs/afs/inode.c
+++ b/fs/afs/inode.c
@@ -848,42 +848,67 @@ static const struct afs_operation_ops afs_setattr_operation = {
 int afs_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 		struct iattr *attr)
 {
+	const unsigned int supported =
+		ATTR_SIZE | ATTR_MODE | ATTR_UID | ATTR_GID |
+		ATTR_MTIME | ATTR_MTIME_SET | ATTR_TIMES_SET | ATTR_TOUCH;
 	struct afs_operation *op;
 	struct afs_vnode *vnode = AFS_FS_I(d_inode(dentry));
+	struct inode *inode = &vnode->vfs_inode;
+	loff_t i_size;
 	int ret;
 
 	_enter("{%llx:%llu},{n=%pd},%x",
 	       vnode->fid.vid, vnode->fid.vnode, dentry,
 	       attr->ia_valid);
 
-	if (!(attr->ia_valid & (ATTR_SIZE | ATTR_MODE | ATTR_UID | ATTR_GID |
-				ATTR_MTIME | ATTR_MTIME_SET | ATTR_TIMES_SET |
-				ATTR_TOUCH))) {
+	if (!(attr->ia_valid & supported)) {
 		_leave(" = 0 [unsupported]");
 		return 0;
 	}
 
+	i_size = i_size_read(inode);
 	if (attr->ia_valid & ATTR_SIZE) {
-		if (!S_ISREG(vnode->vfs_inode.i_mode))
+		if (!S_ISREG(inode->i_mode))
 			return -EISDIR;
 
-		ret = inode_newsize_ok(&vnode->vfs_inode, attr->ia_size);
+		ret = inode_newsize_ok(inode, attr->ia_size);
 		if (ret)
 			return ret;
 
-		if (attr->ia_size == i_size_read(&vnode->vfs_inode))
+		if (attr->ia_size == i_size)
 			attr->ia_valid &= ~ATTR_SIZE;
 	}
 
 	fscache_use_cookie(afs_vnode_cache(vnode), true);
 
-	/* flush any dirty data outstanding on a regular file */
-	if (S_ISREG(vnode->vfs_inode.i_mode))
-		filemap_write_and_wait(vnode->vfs_inode.i_mapping);
-
 	/* Prevent any new writebacks from starting whilst we do this. */
 	down_write(&vnode->validate_lock);
 
+	if ((attr->ia_valid & ATTR_SIZE) && S_ISREG(inode->i_mode)) {
+		loff_t size = attr->ia_size;
+
+		/* Wait for any outstanding writes to the server to complete */
+		loff_t from = min(size, i_size);
+		loff_t to = max(size, i_size);
+		ret = filemap_fdatawait_range(inode->i_mapping, from, to);
+		if (ret < 0)
+			goto out_unlock;
+
+		/* Don't talk to the server if we're just shortening in-memory
+		 * writes that haven't gone to the server yet.
+		 */
+		if (!(attr->ia_valid & (supported & ~ATTR_SIZE & ~ATTR_MTIME)) &&
+		    attr->ia_size < i_size &&
+		    attr->ia_size > vnode->status.size) {
+			truncate_pagecache(inode, attr->ia_size);
+			fscache_resize_cookie(afs_vnode_cache(vnode),
+					      attr->ia_size);
+			i_size_write(inode, attr->ia_size);
+			ret = 0;
+			goto out_unlock;
+		}
+	}
+
 	op = afs_alloc_operation(((attr->ia_valid & ATTR_FILE) ?
 				  afs_file_key(attr->ia_file) : NULL),
 				 vnode->volume);