[dm-devel] mirroring: [patch 3 of 6] device failure tolerance
Jonathan E Brassow
jbrassow at redhat.com
Thu Jun 30 07:44:00 UTC 2005
This patch adds device failure detection to reads.
brassow
diff -urN linux-2.6.12-00002/drivers/md/dm-raid1.c
linux-2.6.12-00003/drivers/md/dm-raid1.c
--- linux-2.6.12-00002/drivers/md/dm-raid1.c 2005-06-30
01:51:48.500842746 -0500
+++ linux-2.6.12-00003/drivers/md/dm-raid1.c 2005-06-30
01:56:10.058877081 -0500
@@ -6,6 +6,7 @@
#include "dm.h"
#include "dm-bio-list.h"
+#include "dm-bio-record.h"
#include "dm-io.h"
#include "dm-log.h"
#include "kcopyd.h"
@@ -572,24 +573,39 @@
struct mirror mirror[0];
};
+struct bio_map_info {
+ struct mirror *bmi_m;
+ struct dm_bio_details bmi_bd;
+};
+
+static mempool_t *bio_map_info_pool = NULL;
+
+static void *bio_map_info_alloc(unsigned int gfp_mask, void
*pool_data){
+ return kmalloc(sizeof(struct bio_map_info), gfp_mask);
+}
+
+static void bio_map_info_free(void *element, void *pool_data){
+ kfree(element);
+}
+
/*
* Every mirror should look like this one.
*/
#define DEFAULT_MIRROR 0
/*
- * This is yucky. We squirrel the mirror_set struct away inside
- * bi_next for write buffers. This is safe since the bh
+ * This is yucky. We squirrel the mirror struct away inside
+ * bi_next for read/write buffers. This is safe since the bh
* doesn't get submitted to the lower levels of block layer.
*/
-static struct mirror_set *bio_get_ms(struct bio *bio)
+static struct mirror *bio_get_m(struct bio *bio)
{
- return (struct mirror_set *) bio->bi_next;
+ return (struct mirror *) bio->bi_next;
}
-static void bio_set_ms(struct bio *bio, struct mirror_set *ms)
+static void bio_set_m(struct bio *bio, struct mirror *m)
{
- bio->bi_next = (struct bio *) ms;
+ bio->bi_next = (struct bio *) m;
}
/*-----------------------------------------------------------------
@@ -753,37 +769,95 @@
choose_mirror(m->ms, m);
}
+static int default_ok(struct mirror *m)
+{
+ return !atomic_read(&m->ms->default_mirror->error_count);
+}
+
/*
* remap a buffer to a particular mirror.
*/
-static void map_bio(struct mirror_set *ms, struct mirror *m, struct
bio *bio)
+static sector_t map_sector(struct mirror *m, struct bio *bio)
+{
+ return m->offset + (bio->bi_sector - m->ms->ti->begin);
+}
+
+static void map_bio(struct mirror *m, struct bio *bio)
{
bio->bi_bdev = m->dev->bdev;
- bio->bi_sector = m->offset + (bio->bi_sector - ms->ti->begin);
+ bio->bi_sector = map_sector(m, bio);
+}
+
+static void map_region(struct io_region *io, struct mirror *m,
+ struct bio *bio)
+{
+ io->bdev = m->dev->bdev;
+ io->sector = map_sector(m, bio);
+ io->count = bio->bi_size >> 9;
}
/*-----------------------------------------------------------------
* Reads
*---------------------------------------------------------------*/
+static void read_callback(unsigned long error, void *context)
+{
+ struct bio *bio = (struct bio *)context;
+ struct mirror *m;
+
+ m = bio_get_m(bio);
+ bio_set_m(bio, NULL);
+
+ if (unlikely(error)) {
+ DMWARN("A read failure occurred on a mirror device.");
+ fail_mirror(m);
+ if (likely(default_ok(m))) {
+ DMWARN("Trying different device.");
+ queue_bio(m->ms, bio, bio_rw(bio));
+ } else {
+ DMERR("No other device available, failing I/O.");
+ bio_endio(bio, 0, -EIO);
+ }
+ } else
+ bio_endio(bio, bio->bi_size, 0);
+}
+
+/* Asynchronous read. */
+static void read_async_bio(struct mirror *m, struct bio *bio)
+{
+ struct io_region io;
+
+ map_region(&io, m, bio);
+ bio_set_m(bio, m);
+ dm_io_async_bvec(1, &io, READ,
+ bio->bi_io_vec + bio->bi_idx,
+ read_callback, bio);
+}
+
static void do_reads(struct mirror_set *ms, struct bio_list *reads)
{
- region_t region;
struct bio *bio;
struct mirror *m;
while ((bio = bio_list_pop(reads))) {
- region = bio_to_region(&ms->rh, bio);
-
/*
* We can only read balance if the region is in sync.
*/
- if (rh_in_sync(&ms->rh, region, 0))
+ if (likely(rh_in_sync(&ms->rh,
+ bio_to_region(&ms->rh, bio),
+ 0) == RH_CLEAN))
m = choose_mirror(ms, NULL);
- else
- m = ms->default_mirror;
+ else {
+ m = ms->default_mirror;;
- map_bio(ms, m, bio);
- generic_make_request(bio);
+ /* If the default fails, we give up .*/
+ if (unlikely(m && atomic_read(&m->error_count)))
+ m = NULL;
+ }
+
+ if (likely(m))
+ read_async_bio(m, bio);
+ else
+ bio_endio(bio, 0, -EIO);
}
}
@@ -838,8 +912,8 @@
struct bio *bio = (struct bio *) context;
struct mirror_set *ms;
- ms = bio_get_ms(bio);
- bio_set_ms(bio, NULL);
+ ms = (bio_get_m(bio))->ms;
+ bio_set_m(bio, NULL);
/*
* NOTE: We don't decrement the pending count here,
@@ -900,21 +974,26 @@
static void do_write(struct mirror_set *ms, struct bio *bio)
{
unsigned int i;
- struct io_region io[KCOPYD_MAX_REGIONS+1];
+ struct io_region io[ms->nr_mirrors], *dest = io;
struct mirror *m;
- for (i = 0; i < ms->nr_mirrors; i++) {
- m = ms->mirror + i;
-
- io[i].bdev = m->dev->bdev;
- io[i].sector = m->offset + (bio->bi_sector - ms->ti->begin);
- io[i].count = bio->bi_size >> 9;
+ for (i = 0, m = ms->mirror; i < ms->nr_mirrors; i++, m++) {
+ if (likely(!atomic_read(&m->error_count)))
+ map_region(dest++, m, bio);
}
- bio_set_ms(bio, ms);
- dm_io_async_bvec(ms->nr_mirrors, io, WRITE,
- bio->bi_io_vec + bio->bi_idx,
- write_callback, bio);
+ if (likely(dest - io)) {
+ /*
+ * We can use the default mirror here, because we
+ * only need it in order to retrieve the reference
+ * to the mirror set in write_callback().
+ */
+ bio_set_m(bio, ms->default_mirror);
+ dm_io_async_bvec(dest - io, io, WRITE,
+ bio->bi_io_vec + bio->bi_idx,
+ write_callback, bio);
+ } else
+ bio_endio(bio, bio->bi_size, -EIO);
}
static void do_writes(struct mirror_set *ms, struct bio_list *writes)
@@ -972,7 +1051,7 @@
rh_delay(&ms->rh, bio);
while ((bio = bio_list_pop(&nosync))) {
- map_bio(ms, ms->default_mirror, bio);
+ map_bio(ms->default_mirror, bio);
generic_make_request(bio);
}
}
@@ -1258,42 +1337,65 @@
int r, rw = bio_rw(bio);
struct mirror *m;
struct mirror_set *ms = ti->private;
-
- map_context->ll = bio->bi_sector >> ms->rh.region_shift;
+ struct dm_bio_details *bd;
+ struct bio_map_info *bmi;
if (rw == WRITE) {
+ /* Save region for mirror_end_io() handler */
+ map_context->ll = bio_to_region(&ms->rh, bio);
queue_bio(ms, bio, rw);
return 0;
}
+ /* It's all about the READs now */
+
r = ms->rh.log->type->in_sync(ms->rh.log,
bio_to_region(&ms->rh, bio), 0);
if (r < 0 && r != -EWOULDBLOCK)
return r;
- if (r == -EWOULDBLOCK) /* FIXME: ugly */
+ if (r == -EWOULDBLOCK)
r = 0;
- /*
- * We don't want to fast track a recovery just for a read
- * ahead. So we just let it silently fail.
- * FIXME: get rid of this.
- */
- if (!r && rw == READA)
- return -EIO;
+ if (likely(r)) {
+ /*
+ * Optimize reads by avoiding to hand them to daemon.
+ *
+ * In case they fail, queue them for another shot
+ * in the mirror_end_io() function.
+ */
+ m = choose_mirror(ms, NULL);
+ if (likely(m)) {
+ bmi = mempool_alloc(bio_map_info_pool, GFP_KERNEL);
+
+ if (likely(bmi)) {
+ /* without this, a read is not retryable */
+ bd = &bmi->bmi_bd;
+ dm_bio_record(bd, bio);
+ map_context->ptr = bmi;
+ bmi->bmi_m = m;
+ } else {
+ /* we could fail now, but we can at least **
+ ** give it a shot. The bd is only used to **
+ ** retry in the event of a failure anyway. **
+ ** If we fail, we can fail the I/O then. */
+ map_context->ptr = NULL;
+ }
+
+ map_bio(m, bio);
+ return 1; /* Mapped -> queue request. */
+ } else{
+ return -EIO;
+ }
+ } else {
+ /* Either not clean, or -EWOULDBLOCK */
+ if (rw == READA)
+ return -EIO;
- if (!r) {
- /* Pass this io over to the daemon */
queue_bio(ms, bio, rw);
- return 0;
}
- m = choose_mirror(ms, NULL);
- if (!m)
- return -EIO;
-
- map_bio(ms, m, bio);
- return 1;
+ return 0;
}
static int mirror_end_io(struct dm_target *ti, struct bio *bio,
@@ -1301,15 +1403,53 @@
{
int rw = bio_rw(bio);
struct mirror_set *ms = (struct mirror_set *) ti->private;
- region_t region = map_context->ll;
+ struct mirror *m = NULL;
/*
* We need to dec pending if this was a write.
*/
- if (rw == WRITE)
- rh_dec(&ms->rh, region);
+ if (rw == WRITE) {
+ rh_dec(&ms->rh, map_context->ll);
+ return error;
+ }
- return 0;
+ if (unlikely(error)) {
+ struct dm_bio_details *bd = NULL;
+
+ DMERR("A read failure occurred on a mirror device.");
+ if (!map_context->ptr) {
+ /*
+ * There wasn't enough memory to record necessary
+ * information for a retry.
+ */
+ DMERR("Out of memory causing inability to retry read.");
+ return -EIO;
+ }
+ m = ((struct bio_map_info *)map_context->ptr)->bmi_m;
+ fail_mirror(m); /* Flag error on mirror. */
+
+ /*
+ * A failed read needs to get queued
+ * to the daemon for another shot to
+ * one (if any) intact mirrors.
+ */
+ if (rw == READ && default_ok(m)) {
+ bd = &(((struct bio_map_info *)map_context->ptr)->bmi_bd);
+
+ DMWARN("Trying different device.");
+ dm_bio_restore(bd, bio);
+ mempool_free(map_context->ptr, bio_map_info_pool);
+ map_context->ptr = NULL;
+ queue_bio(ms, bio, rw);
+ return 1; /* We want another shot on the bio. */
+ }
+ DMERR("All replicated volumes dead, failing I/O");
+ }
+
+ if (map_context->ptr)
+ mempool_free(map_context->ptr, bio_map_info_pool);
+
+ return error;
}
static void mirror_presuspend(struct dm_target *ti){
@@ -1409,6 +1549,12 @@
{
int r;
+ bio_map_info_pool = mempool_create(100, bio_map_info_alloc,
+ bio_map_info_free, NULL);
+ if (!bio_map_info_pool) {
+ return -ENOMEM;
+ }
+
r = dm_dirty_log_init();
if (r)
return r;
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