On Wed 22-04-20 11:51:21, Ira Weiny wrote: > On Wed, Apr 22, 2020 at 09:29:51AM -0700, Darrick J. Wong wrote: > > On Tue, Apr 21, 2020 at 12:17:45PM -0700, ira.weiny@xxxxxxxxx wrote: > > > From: Ira Weiny <ira.weiny@xxxxxxxxx> > > > > > > In order for users to determine if a file is currently operating in DAX > > > state (effective DAX). Define a statx attribute value and set that > > > attribute if the effective DAX flag is set. > > > > > > To go along with this we propose the following addition to the statx man > > > page: > > > > > > STATX_ATTR_DAX > > > > > > The file is in the DAX (cpu direct access) state. DAX state > > > attempts to minimize software cache effects for both I/O and > > > memory mappings of this file. It requires a file system which > > > has been configured to support DAX. > > > > > > DAX generally assumes all accesses are via cpu load / store > > > instructions which can minimize overhead for small accesses, but > > > may adversely affect cpu utilization for large transfers. > > > > > > File I/O is done directly to/from user-space buffers and memory > > > mapped I/O may be performed with direct memory mappings that > > > bypass kernel page cache. > > > > > > While the DAX property tends to result in data being transferred > > > synchronously, it does not give the same guarantees of O_SYNC > > > where data and the necessary metadata are transferred together. > > > > > > A DAX file may support being mapped with the MAP_SYNC flag, > > > which enables a program to use CPU cache flush instructions to > > > persist CPU store operations without an explicit fsync(2). See > > > mmap(2) for more information. > > > > One thing I hadn't noticed before -- this is a change to userspace API, > > so please cc this series to linux-api@xxxxxxxxxxxxxxx when you send V10. > > Right! Glad you caught me on this because I was just preparing to send V10. > > Is there someone I could directly mail who needs to look at this? I guess I > thought we had the important FS people involved for this type of API change. > :-/ I believe we have all the important people here. But linux-api is a general fallback list where people reviewing API changes linger. So when changing user facing API, it is good to CC this list. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
