On 15 June 2018 at 10:31, Steven Whitehouse <swhiteho@xxxxxxxxxx> wrote: > Hi, > > On 15/06/18 09:03, Christoph Hellwig wrote: >> >> On Thu, Jun 14, 2018 at 03:04:38PM +0200, Andreas Gruenbacher wrote: >>> >>> I saw that you've pushed this onto the gfs2-iomap branch in your xfs >>> repository. I've rebased the gfs2 iomap-write branch onto that; >>> there's a trivial patch for adding a private pointer to struct iomap >>> at the head of that branch that would sense to move to the shared >>> branch as well now. >> >> Please send that patch out ASAP. >> >>> The next step would probably be to start using iomap_readpage / >>> iomap_readpages in gfs2 for block size == page size. This requires >>> adding inline data support to iomap_readpage which is trivial, but >>> because of gfs2's reliance on buffer heads, that alone isn't enough. >> >> Is it? At least for block size == page size we will only call >> readpage on a pristine, newly allocated page. So buffer heads won't >> be in the game at that point, and the iomap buffered write code will >> just allocate them for you once we start a write operation, or take >> a page fault that makes the page writable. What I'm seeing in the readpage address space operation is pages which are not PageUptodate(), with a page-size buffer head that is buffer_uptodate(). The filesystem doesn't bother keeping the page flags in sync with the buffer head flags, nothing unusual. When iomap_readpage is called on such a page, it will replace the current contents with what's on disk, losing the changes in memory. So we cannot just call iomap_readpages, we need to check the buffer head flags as well. Or, since the old code is still needed for page size != block size anyway, we can fall back to that for pages that have buffers for now. > Yes, for block size == page size, it should not be an issue to drop the use > of buffer heads on reads in GFS2. I was fairly sure that we already did that > in ->readpages() anyway, but it is a while since I looked at the code and my > memory may be playing tricks on me, I've pushed what I have so far here in case you want to have a look: https://git.kernel.org/pub/scm/linux/kernel/git/gfs2/linux-gfs2.git/log/?h=iomap-readpage There's one remaining failure in xfstest generic/299 that I'm still looking into. Thanks, Andreas
