On Mon, Jun 28, 2021 at 06:39:09PM +0100, Matthew Wilcox wrote: > Not hugely happy with either of these options, tbh. I'd rather we apply > a patch akin to this one (plucked from the folio tree), so won't apply: > so permit pages without an iop to enter writeback and create an iop > *then*. Would that solve your problem? It is the right thing to do, especially when combined with a feature patch to not bother to create the iomap_page structure on small block size file systems when the extent covers the whole page. > > > (3) We're not yet using iomap_page_mkwrite, so iomap_page objects don't > > get created on .page_mkwrite, either. Part of the reason is that > > iomap_page_mkwrite locks the page and then calls into the filesystem for > > uninlining and for allocating backing blocks. This conflicts with the > > gfs2 locking order: on gfs2, transactions must be started before locking > > any pages. We can fix that by calling iomap_page_create from > > gfs2_page_mkwrite, or by doing the uninlining and allocations before > > calling iomap_page_mkwrite. I've implemented option 2 for now; see > > here: > > I think this might also solve this problem? We'll still need to create the iomap_page structure for page_mkwrite if there is an extent boundary inside the page.
