On Wed, Jun 12, 2024 at 12:07:40PM +0530, Ritesh Harjani wrote: > > "Darrick J. Wong" <djwong@xxxxxxxxxx> writes: > > > On Tue, Jun 11, 2024 at 04:15:02PM +0530, Ritesh Harjani wrote: > >> > >> Hi Darrick, > >> > >> Resuming my review from where I left off yesterday. > > > > <snip> > >> > +Writes > >> > +~~~~~~ > >> > + > >> > +The ``iomap_file_buffered_write`` function writes an ``iocb`` to the > >> > +pagecache. > >> > +``IOMAP_WRITE`` or ``IOMAP_WRITE`` | ``IOMAP_NOWAIT`` will be passed as > >> > +the ``flags`` argument to ``->iomap_begin``. > >> > +Callers commonly take ``i_rwsem`` in either shared or exclusive mode. > >> > >> shared(e.g. aligned overwrites) > > > > Ok, I see we were in buffered I/O section (Sorry, I misunderstood > thinking this was for direct-io) Aha. I'll change these headings to "Buffered Readahead and Reads" and "Buffered Writes". > > That's a matter of debate -- xfs locks out concurrent reads by taking > > i_rwsem in exclusive mode, whereas (I think?) ext4 and most other > > filesystems take it in shared mode and synchronizes readers and writers > > with folio locks. > > Ext4 too takes inode lock in exclusive mode in case of > buffered-write. It's the DIO writes/overwrites in ext4 which has special > casing for shared/exclusive mode locking. > > But ext4 buffered-read does not take any inode lock (it uses > generic_file_read_iter()). So the synchronization must happen via folio > lock w.r.t buffered-writes. > > However, I am not sure if we have any filesystem taking VFS inode lock in > shared more for buffered-writes. In theory you could if no other metadata needed updating, such as a dumb filesystem with fixed size files where timestamps don't matter. > BTW - > I really like all of the other updates that you made w.r.t the review > comments. All of those looks more clear to me. (so not commenting on them > individually). > > Thanks! No, thank /you/ and everyone else for reading all the way through it. I'll finish cleaning things up and put out a v2. --D > -ritesh >
