Removes seq_count from super block. Currently the super block gets
written in each commit to update the seq_count which is just used when
the target is restarted/resumed. This extra iop has a performance impact
on small block size writes which do FUA/sync on every request. A 4k sync
write currently requires 3 write ops: submitted data, metadata + super
block seq_count update, removal of seq_count update reduces required
write ops to 2.
Rebuild of seq_count at start/resumption can be done quickly by looping
through memory entry metadata within the resume() function.
Signed-off-by: Maged Mokhtar <mmokhtar@xxxxxxxxxxx>
---
drivers/md/dm-writecache.c | 56 ++++++++++++++++++++++++++---------
1 file changed, 42 insertions(+), 14 deletions(-)
--- a/drivers/md/dm-writecache.c 2019-12-06 03:07:53.000000000 -0800
+++ b/drivers/md/dm-writecache.c 2019-12-06 09:25:45.000000000 -0800
@@ -52,7 +52,8 @@ do { \
#endif
#define MEMORY_SUPERBLOCK_MAGIC 0x23489321
-#define MEMORY_SUPERBLOCK_VERSION 1
+#define MEMORY_SUPERBLOCK_VERSION_1 1
+#define MEMORY_SUPERBLOCK_VERSION_2 2
struct wc_memory_entry {
__le64 original_sector;
@@ -67,7 +68,6 @@ struct wc_memory_superblock {
__le32 block_size;
__le32 pad;
__le64 n_blocks;
- __le64 seq_count;
};
__le64 padding[8];
};
@@ -380,6 +380,41 @@ static uint64_t read_seq_count(struct dm
#endif
}
+static uint64_t read_last_seq_count(struct dm_writecache *wc)
+{
+ size_t b;
+ uint64_t last_seq_count = 0;
+ uint64_t seq_count;
+ __le64 empty = cpu_to_le64(-1);
+
+ if (WC_MODE_PMEM(wc)) {
+ struct wc_memory_entry wme;
+ for (b = 0; b < wc->n_blocks; b++) {
+ BUG_ON(memcpy_mcsafe(&wme, &sb(wc)->entries[b],
+ sizeof(struct wc_memory_entry)));
+ if (wme.seq_count != empty) {
+ seq_count = le64_to_cpu(wme.seq_count);
+ if (last_seq_count < seq_count)
+ last_seq_count = seq_count;
+ }
+ }
+ }
+ else {
+ struct wc_memory_entry *p = &sb(wc)->entries[0];
+ b = wc->n_blocks;
+ while (0 < b) {
+ if (p->seq_count != empty) {
+ seq_count = le64_to_cpu(p->seq_count);
+ if (last_seq_count < seq_count)
+ last_seq_count = seq_count;
+ }
+ p++;
+ b--;
+ }
+ }
+ return last_seq_count;
+}
+
static void clear_seq_count(struct dm_writecache *wc, struct wc_entry *e)
{
#ifdef DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
@@ -730,8 +765,6 @@ static void writecache_flush(struct dm_w
writecache_wait_for_ios(wc, WRITE);
wc->seq_count++;
- pmem_assign(sb(wc)->seq_count, cpu_to_le64(wc->seq_count));
- writecache_flush_region(wc, &sb(wc)->seq_count, sizeof sb(wc)->seq_count);
writecache_commit_flushed(wc);
wc->overwrote_committed = false;
@@ -876,7 +909,6 @@ static void writecache_resume(struct dm_
struct dm_writecache *wc = ti->private;
size_t b;
bool need_flush = false;
- __le64 sb_seq_count;
int r;
wc_lock(wc);
@@ -894,12 +926,7 @@ static void writecache_resume(struct dm_
}
wc->freelist_size = 0;
- r = memcpy_mcsafe(&sb_seq_count, &sb(wc)->seq_count, sizeof(uint64_t));
- if (r) {
- writecache_error(wc, r, "hardware memory error when reading
superblock: %d", r);
- sb_seq_count = cpu_to_le64(0);
- }
- wc->seq_count = le64_to_cpu(sb_seq_count);
+ wc->seq_count = read_last_seq_count(wc) + 1;
#ifdef DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
for (b = 0; b < wc->n_blocks; b++) {
@@ -1757,10 +1784,9 @@ static int init_memory(struct dm_writeca
for (b = 0; b < ARRAY_SIZE(sb(wc)->padding); b++)
pmem_assign(sb(wc)->padding[b], cpu_to_le64(0));
- pmem_assign(sb(wc)->version, cpu_to_le32(MEMORY_SUPERBLOCK_VERSION));
+ pmem_assign(sb(wc)->version, cpu_to_le32(MEMORY_SUPERBLOCK_VERSION_2));
pmem_assign(sb(wc)->block_size, cpu_to_le32(wc->block_size));
pmem_assign(sb(wc)->n_blocks, cpu_to_le64(wc->n_blocks));
- pmem_assign(sb(wc)->seq_count, cpu_to_le64(0));
for (b = 0; b < wc->n_blocks; b++)
write_original_sector_seq_count(wc, &wc->entries[b], -1, -1);
@@ -2159,11 +2185,13 @@ invalid_optional:
goto bad;
}
- if (le32_to_cpu(s.version) != MEMORY_SUPERBLOCK_VERSION) {
+ if (le32_to_cpu(s.version) != MEMORY_SUPERBLOCK_VERSION_1 &&
+ le32_to_cpu(s.version) != MEMORY_SUPERBLOCK_VERSION_2) {
ti->error = "Invalid version in the superblock";
r = -EINVAL;
goto bad;
}
+ pmem_assign(sb(wc)->version, cpu_to_le32(MEMORY_SUPERBLOCK_VERSION_2));
if (le32_to_cpu(s.block_size) != wc->block_size) {
ti->error = "Block size does not match superblock";
--
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