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[PATCH] md: add write-intent-bitmap support to raid5

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Most awkward part of this is delaying write requests until bitmap updates have
been flushed.

To achieve this, we have a sequence number (seq_flush) which is incremented
each time the raid5 is unplugged.

If the raid thread notices that this has changed, it flushes bitmap changes,
and assigned the value of seq_flush to seq_write.

When a write request arrives, it is given the number from seq_write, and that
write request may not complete until seq_flush is larger than the saved seq
number.

We have a new queue for storing stripes which are waiting for a bitmap flush
and an extra flag for stripes to record if the write was 'degraded' and so
should not clear the a bit in the bitmap.

Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
NeilBrown 2005-09-09 16:23:54 -07:00 • committed by Linus Torvalds
parent 0002b2718d
commit 72626685dc
3 changed files with 137 additions and 13 deletions
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14
include/linux/raid/raid5.h
View file

@ -134,6 +134,7 @@ struct stripe_head {
unsigned long state; /* state flags */
atomic_t count; /* nr of active thread/requests */
spinlock_t lock;
int bm_seq; /* sequence number for bitmap flushes */
struct r5dev {
struct bio req;
struct bio_vec vec;
@ -165,12 +166,13 @@ struct stripe_head {
/*
* Stripe state
*/
#define STRIPE_ERROR 1
#define STRIPE_HANDLE 2
#define STRIPE_SYNCING 3
#define STRIPE_INSYNC 4
#define STRIPE_PREREAD_ACTIVE 5
#define STRIPE_DELAYED 6
#define STRIPE_DEGRADED 7
#define STRIPE_BIT_DELAY 8
/*
* Plugging:
@ -210,10 +212,20 @@ struct raid5_private_data {
struct list_head handle_list; /* stripes needing handling */
struct list_head delayed_list; /* stripes that have plugged requests */
struct list_head bitmap_list; /* stripes delaying awaiting bitmap update */
atomic_t preread_active_stripes; /* stripes with scheduled io */
char cache_name[20];
kmem_cache_t *slab_cache; /* for allocating stripes */
int seq_flush, seq_write;
int quiesce;
int fullsync; /* set to 1 if a full sync is needed,
* (fresh device added).
* Cleared when a sync completes.
*/
/*
* Free stripes pool
*/