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[PATCH] dm snapshot: tidy pe ref counting
Rename sibling_count to ref_count and introduce get and put functions. Signed-off-by: Alasdair G Kergon <agk@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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parent
ca3a931fd3
commit
4b832e8de2
1 changed files with 48 additions and 35 deletions
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@ -59,7 +59,7 @@ struct pending_exception {
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/*
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* The primary pending_exception is the one that holds
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* the sibling_count and the list of origin_bios for a
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* the ref_count and the list of origin_bios for a
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* group of pending_exceptions. It is always last to get freed.
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* These fields get set up when writing to the origin.
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*/
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@ -72,7 +72,7 @@ struct pending_exception {
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* the sibling concerned and not pe->primary_pe->snap->lock unless
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* they are the same.
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*/
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atomic_t sibling_count;
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atomic_t ref_count;
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/* Pointer back to snapshot context */
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struct dm_snapshot *snap;
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@ -653,10 +653,46 @@ static void __invalidate_snapshot(struct dm_snapshot *s,
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dm_table_event(s->table);
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}
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static void get_pending_exception(struct pending_exception *pe)
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{
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atomic_inc(&pe->ref_count);
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}
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static struct bio *put_pending_exception(struct pending_exception *pe)
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{
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struct pending_exception *primary_pe;
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struct bio *origin_bios = NULL;
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primary_pe = pe->primary_pe;
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/*
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* If this pe is involved in a write to the origin and
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* it is the last sibling to complete then release
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* the bios for the original write to the origin.
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*/
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if (primary_pe &&
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atomic_dec_and_test(&primary_pe->ref_count))
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origin_bios = bio_list_get(&primary_pe->origin_bios);
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/*
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* Free the pe if it's not linked to an origin write or if
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* it's not itself a primary pe.
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*/
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if (!primary_pe || primary_pe != pe)
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free_pending_exception(pe);
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/*
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* Free the primary pe if nothing references it.
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*/
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if (primary_pe && !atomic_read(&primary_pe->ref_count))
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free_pending_exception(primary_pe);
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return origin_bios;
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}
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static void pending_complete(struct pending_exception *pe, int success)
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{
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struct exception *e;
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struct pending_exception *primary_pe;
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struct dm_snapshot *s = pe->snap;
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struct bio *origin_bios = NULL;
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struct bio *snapshot_bios = NULL;
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@ -695,30 +731,7 @@ static void pending_complete(struct pending_exception *pe, int success)
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out:
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snapshot_bios = bio_list_get(&pe->snapshot_bios);
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primary_pe = pe->primary_pe;
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/*
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* If this pe is involved in a write to the origin and
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* it is the last sibling to complete then release
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* the bios for the original write to the origin.
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*/
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if (primary_pe &&
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atomic_dec_and_test(&primary_pe->sibling_count))
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origin_bios = bio_list_get(&primary_pe->origin_bios);
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/*
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* Free the pe if it's not linked to an origin write or if
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* it's not itself a primary pe.
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*/
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if (!primary_pe || primary_pe != pe)
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free_pending_exception(pe);
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/*
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* Free the primary pe if nothing references it.
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*/
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if (primary_pe && !atomic_read(&primary_pe->sibling_count))
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free_pending_exception(primary_pe);
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origin_bios = put_pending_exception(pe);
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up_write(&s->lock);
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@ -829,7 +842,7 @@ __find_pending_exception(struct dm_snapshot *s, struct bio *bio)
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bio_list_init(&pe->origin_bios);
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bio_list_init(&pe->snapshot_bios);
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pe->primary_pe = NULL;
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atomic_set(&pe->sibling_count, 1);
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atomic_set(&pe->ref_count, 0);
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pe->snap = s;
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pe->started = 0;
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@ -838,6 +851,7 @@ __find_pending_exception(struct dm_snapshot *s, struct bio *bio)
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return NULL;
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}
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get_pending_exception(pe);
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insert_exception(&s->pending, &pe->e);
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out:
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@ -1012,7 +1026,7 @@ static int __origin_write(struct list_head *snapshots, struct bio *bio)
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* is already remapped in this snapshot
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* and trigger an exception if not.
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*
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* sibling_count is initialised to 1 so pending_complete()
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* ref_count is initialised to 1 so pending_complete()
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* won't destroy the primary_pe while we're inside this loop.
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*/
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e = lookup_exception(&snap->complete, chunk);
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@ -1043,8 +1057,8 @@ static int __origin_write(struct list_head *snapshots, struct bio *bio)
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}
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if (!pe->primary_pe) {
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atomic_inc(&primary_pe->sibling_count);
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pe->primary_pe = primary_pe;
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get_pending_exception(primary_pe);
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}
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if (!pe->started) {
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@ -1057,20 +1071,20 @@ static int __origin_write(struct list_head *snapshots, struct bio *bio)
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}
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if (!primary_pe)
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goto out;
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return r;
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/*
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* If this is the first time we're processing this chunk and
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* sibling_count is now 1 it means all the pending exceptions
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* ref_count is now 1 it means all the pending exceptions
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* got completed while we were in the loop above, so it falls to
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* us here to remove the primary_pe and submit any origin_bios.
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*/
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if (first && atomic_dec_and_test(&primary_pe->sibling_count)) {
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if (first && atomic_dec_and_test(&primary_pe->ref_count)) {
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flush_bios(bio_list_get(&primary_pe->origin_bios));
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free_pending_exception(primary_pe);
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/* If we got here, pe_queue is necessarily empty. */
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goto out;
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return r;
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}
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/*
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@ -1079,7 +1093,6 @@ static int __origin_write(struct list_head *snapshots, struct bio *bio)
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list_for_each_entry_safe(pe, next_pe, &pe_queue, list)
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start_copy(pe);
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out:
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return r;
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}
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