On Mon, 7 Dec 2009, Mike Snitzer wrote: > On Mon, Dec 07 2009 at 6:44pm -0500, > Alasdair G Kergon <agk@xxxxxxxxxx> wrote: > > > On Mon, Dec 07, 2009 at 04:10:53PM -0500, Mike Snitzer wrote: > > > Subject: dm exception store: snapshot-merge usage accounting > > > > Comments updated a bit and folded into > > dm-exception-store-add-merge-specific-methods.patch # 64745 > > OK, I did the following based on our chat.. but haven't looked at your > version yet (ftp://sources.redhat.com appears to be down?). > > Mike > --- > > From: Mike Snitzer <snitzer@xxxxxxxxxx> > Subject: dm exception store: snapshot-merge usage accounting > > Adjust the persistent exception store's next_free to the last chunk that > was processed in persistent_commit_merge(). prepare_merge() may change > ps->current_area but not before commit_merge() processes 'nr_merged' > chunks from it. > > Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx> > Cc: Mikulas Patocka <mpatocka@xxxxxxxxxx> > --- > drivers/md/dm-snap-persistent.c | 33 ++++++++++++++++++++++++++++----- > 1 file changed, 28 insertions(+), 5 deletions(-) > > Index: linux-rhel6/drivers/md/dm-snap-persistent.c > =================================================================== > --- linux-rhel6.orig/drivers/md/dm-snap-persistent.c > +++ linux-rhel6/drivers/md/dm-snap-persistent.c > @@ -119,7 +119,24 @@ struct pstore { > chunk_t current_area; > > /* > - * The next free chunk for an exception. > + * 'next_free' can have two meanings. > + * > + * When creating exceptions: > + * The next free chunk for an exception. 'next_free' means all > + * the slots here and above are free. Though there may be > + * holes in the exception store because chunks can be committed > + * out of order -- if the system halts abruptly it could > + * leave a hole. > + * > + * When merging exceptions: > + * The last chunk that was merged from a linear extent of > + * chunks [returned from persistent_prepare_merge()]. > + * When merging 'next_free' does _not_ mean all the slots here > + * and above are free. It holds the value it would have held > + * if all chunks in an area had been committed in order. So > + * the value may occasionally be slightly inaccurate, because > + * chunks can be committed out of order, but since it's only > + * used for 'status' this doesn't matter. > */ > chunk_t next_free; > > @@ -753,10 +770,16 @@ static int persistent_commit_merge(struc > ps->current_committed -= nr_merged; > > /* > - * Note that we make no attempt to keep ps->next_free up-to-date > - * as exceptions may have been allocated out-of-order. > - * Once a snapshot has become merging, nothing further uses it. > - */ > + * Update ps->next_free so persistent_usage() is accurate > + * - it may be less than the actual 'next_free' chunk but we > + * will not allocate exceptions again so this doesn't matter > + * - must account for the first two metadata chunks > + * - prepare_merge() may change ps->current_area but not before > + * commit_merge() processes 'nr_merged' from the current_area > + */ > + ps->next_free = > + (area_location(ps, ps->current_area) - 1 + > + ps->current_committed + 2); > > return 0; > } > Acked-By: Mikulas Patocka <mpatocka@xxxxxxxxxx> -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
