On Mon, Jan 31, 2022 at 03:03:53PM +1100, NeilBrown wrote: > diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c > index 182b24a14804..5f74e2585f50 100644 > --- a/fs/fuse/dax.c > +++ b/fs/fuse/dax.c > @@ -781,6 +781,9 @@ static int fuse_dax_writepages(struct address_space *mapping, > struct inode *inode = mapping->host; > struct fuse_conn *fc = get_fuse_conn(inode); > > + if (wbc->sync_mode == WB_SYNC_NONE && > + fc->num_background >= fc->congestion_threshold) > + return 0; > return dax_writeback_mapping_range(mapping, fc->dax->dev, wbc); This makes no sense. Doing writeback for DAX means flushing the CPU cache (in a terribly inefficient way), but it's not going to be doing anything in the background; it's a sync operation. > +++ b/fs/fuse/file.c > @@ -958,6 +958,8 @@ static void fuse_readahead(struct readahead_control *rac) > > if (fuse_is_bad(inode)) > return; > + if (fc->num_background >= fc->congestion_threshold) > + return; This seems like a bad idea to me. If we don't even start reads on readahead pages, they'll get ->readpage called on them one at a time and the reading thread will block. It's going to lead to some nasty performance problems, exactly when you don't want them. Better to queue the reads internally and wait for congestion to ease before submitting the read.
