On Fri, Feb 24, 2017 at 11:43 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > Usage counts are common and useful, so for now they should stay as-is > and if people can came up with a useful primitive for them we can > consider implementing it. > While developing the refcount_t API, we used coccinelle to find areas where converted atomic_t->refcount_t variables were being initialized to 0 (rather than 1). If we're considering a usagecount_t type, this may be a good starting point for determining just how pervasive usage counts actually are (at least the ones that we've converted [or attempted to convert] to refcount_t). Usage count types not atomic_t before the refcount_t conversion obviously weren't included in our search. Note that some of these have already been converted to refcounts, either by adding a +1 bias, or some other workaround. Others are simply too confusing and we haven't decided what to do with them yet; I've marked these as (not converted to refcount_t) below. Some preemptive flame retardant: I realize that not all of these are "usage" counts. They _do_ all fall into the category of refcount_t (formerly atomic_t) variables that are initialized to 0, a common usage count idiom. This is the same thing that's going on with struct inode.i_count and therefore relevant to this discussion. Not (yet) converted to refcount_t: fs/nfsd/state.c: struct nfsd4_session.se_ref fs/nfsd/state.c: struct nfsd4_client.cl_refcount fs/hfsplus/hfsplus_fs.h: struct hfsplus_inode_info.opencnt fs/xfs/xfs_log_priv.h: struct xlog_in_core.ic_refcnt sound/usb/usbaudio.h: struct snd_usb_audio.usage_count tools/perf/util/evlist.h: struct perf_mmap.refcnt include/net/nf_conntrack.h: struct nf_conntrack.use include/net/ip_vs.h: struct ip_vs_service.refcnt Converted to refcount_t: fs/fuse/fuse_i.h: struct fuse_file.count fs/btrfs/delayed-inode.h: struct btrfs_delayed_inode.refs fs/btrfs/compression.c: struct compressed_bio.pending_bios fs/btrfs/extent_io.h: struct extent_buffer.io_pages net/packet/internal.h: struct packet_fanout.sk_ref xfs/xfs_buf.h: struct xfs_buf.b_lru_ref sound/core/seq/seq_ports.h: snd_seq_subscribers.ref_count tools/perf/util/comm.c: struct comm_str.refcnt include/net/bluetooth/hci_core.h: struct hci_conn.refcnt include/linux/filter.h: struct sk_filter.refcnt include/linux/skbuff.h struct sk_buff.users There are 7 more instances in drivers/, 3 of which haven't (yet) been converted to refcount_t, but I'm too lazy to continue with this list. > Trying to shoe-horn everything into refcount_t is a horrible idea.
