netfs: Downgrade i_rwsem for a buffered write
In the I/O locking code borrowed from NFS into netfslib, i_rwsem is held locked across a buffered write - but this causes a performance regression in cifs as it excludes buffered reads for the duration (cifs didn't use any locking for buffered reads). Mitigate this somewhat by downgrading the i_rwsem to a read lock across the buffered write. This at least allows parallel reads to occur whilst excluding other writes, DIO, truncate and setattr. Note that this shouldn't be a problem for a buffered write as a read through an mmap can circumvent i_rwsem anyway. Also note that we might want to make this change in NFS also. Signed-off-by: David Howells <dhowells@redhat.com> Link: https://lore.kernel.org/r/1317958.1729096113@warthog.procyon.org.uk cc: Steve French <sfrench@samba.org> cc: Paulo Alcantara <pc@manguebit.com> cc: Trond Myklebust <trondmy@kernel.org> cc: Jeff Layton <jlayton@kernel.org> cc: netfs@lists.linux.dev cc: linux-cifs@vger.kernel.org cc: linux-nfs@vger.kernel.org cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner <brauner@kernel.org>
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@ -109,6 +109,7 @@ int netfs_start_io_write(struct inode *inode)
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up_write(&inode->i_rwsem);
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up_write(&inode->i_rwsem);
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return -ERESTARTSYS;
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return -ERESTARTSYS;
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}
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}
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downgrade_write(&inode->i_rwsem);
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return 0;
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return 0;
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}
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}
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EXPORT_SYMBOL(netfs_start_io_write);
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EXPORT_SYMBOL(netfs_start_io_write);
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@ -123,7 +124,7 @@ EXPORT_SYMBOL(netfs_start_io_write);
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void netfs_end_io_write(struct inode *inode)
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void netfs_end_io_write(struct inode *inode)
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__releases(inode->i_rwsem)
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__releases(inode->i_rwsem)
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{
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{
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up_write(&inode->i_rwsem);
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up_read(&inode->i_rwsem);
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}
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}
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EXPORT_SYMBOL(netfs_end_io_write);
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EXPORT_SYMBOL(netfs_end_io_write);
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