On Fri, Oct 30, 2020 at 11:02:59PM +0800, Gao Xiang wrote: > Hi Brian, > > On Fri, Oct 30, 2020 at 10:47:40AM -0400, Brian Foster wrote: > > On Thu, Oct 29, 2020 at 07:13:53AM +0800, Gao Xiang wrote: > > ... > > > > out_trans_cancel: > > > + if (extend && (tp->t_flags & XFS_TRANS_DIRTY)) { > > > + xfs_trans_commit(tp); > > > + return error; > > > + } > > > > Do you mean this to be if (!extend && ...)? > > Yeah, you are right. > > > > > Otherwise on a quick read through this seems mostly sane to me. Before > > getting into the implementation details, my comments are mostly around > > patch organization and general development approach. On the former, I > > think this patch could be split up into multiple smaller patches to > > separate refactoring, logic cleanups, and new functionality. E.g., > > factoring out the existing growfs code into a helper, tweaking existing > > logic to prepare the shared grow/shrink path, adding the shrinkfs > > functionality, could all be independent patches. We probably want to > > pull the other patch you sent for the experimental warning into the same > > series as well. > > ok. > > > > > On development approach, I'm a little curious what folks think about > > including these opportunistic shrink bits in the kernel and evolving > > this into a more complete feature over time. Personally, I think that's > > a reasonable approach since shrink has sort of been a feature that's > > been stuck at the starting line due to being something that would be > > nice to have for some folks but too complex/involved to fully implement, > > all at once at least. Perhaps if we start making incremental and/or > > opportunistic progress, we might find a happy medium where common/simple > > use cases work well enough for users who want it, without having to > > support arbitrary shrink sizes, moving the log, etc. > > My personal thought is also incremental approach. since I'm currently > looking at shrinking a whole unused AG, but such whole modification > is all over the codebase, so the whole shrink function would be better > to be built step by step. > > > > > That said, this is still quite incomplete in that we can only reduce the > > size of the tail AG, and if any of that space is in use, we don't > > currently do anything to try and rectify that. Given that, I'd be a > > little hesitant to expose this feature as is to production users. IMO, > > the current kernel feature state could be mergeable but should probably > > also be buried under XFS_DEBUG until things are more polished. To me, > > the ideal level of completeness to expose something in production > > kernels might be something that can 1. relocate used blocks out of the > > target range and then possibly 2. figure out how to chop off entire AGs. > > My thinking is that if we never get to that point for whatever > > reason(s), at least DEBUG mode allows us the flexibility to drop the > > thing entirely without breaking real users. > > Yeah, I also think XFS_DEBUG or another experimential build config > is needed. > > Considering that, I think it would better to seperate into 2 functions > as Darrick suggested in the next version to avoid too many > #ifdef XFS_DEBUG #endif hunks. > Another option could be to just retain the existing error checking logic and wrap it in an ifdef. I.e.: #ifndef DEBUG /* shrink only allowed in debug mode for now ... */ if (nb < mp->m_sb.sb_dblocks) return -EINVAL; #endif Then the rest of the function doesn't have to be factored differently just because of the ifdef. Brian > Thanks, > Gao Xiang > > > > > Anyways, just some high level thoughts on my part. I'm curious if others > > have thoughts on that topic, particularly since this might be a decent > > point to decide whether to put effort into polishing this up or to > > continue with the RFC work and try to prove out more functionality... > > > > Brian > > > > > xfs_trans_cancel(tp); > > > return error; > > > } > > > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c > > > index c94e71f741b6..81b9c32f9bef 100644 > > > --- a/fs/xfs/xfs_trans.c > > > +++ b/fs/xfs/xfs_trans.c > > > @@ -419,7 +419,6 @@ xfs_trans_mod_sb( > > > tp->t_res_frextents_delta += delta; > > > break; > > > case XFS_TRANS_SB_DBLOCKS: > > > - ASSERT(delta > 0); > > > tp->t_dblocks_delta += delta; > > > break; > > > case XFS_TRANS_SB_AGCOUNT: > > > -- > > > 2.18.1 > > > > > >