Hi,
Thanx for your patches, there are some comments inline.
According to these comments, I propose an update base on your patch as [1].
BTW, I added a test case for this problem in dtg-tests:
https://github.com/DataTravelGuide/dtg-tests/blob/main/pcache.py.data/pcache_misc_tests/case21_gc_percent_persistence_after_recreate.sh
It update gc_percent online and recreate pcache device and check gc_percen
[1]:
diff --git a/drivers/md/dm-pcache/cache.c b/drivers/md/dm-pcache/cache.c
index 6d5001548628..4d6db733c9bd 100644
--- a/drivers/md/dm-pcache/cache.c
+++ b/drivers/md/dm-pcache/cache.c
@@ -42,12 +42,7 @@ static int cache_info_init(struct pcache_cache
*cache, struct pcache_cache_optio
if (IS_ERR(cache_info_addr))
return PTR_ERR(cache_info_addr);
- if (cache_info_addr) {
- int index = ((char *)cache_info_addr - (char
*)cache->cache_info_addr) /
- PCACHE_CACHE_INFO_SIZE;
-
- cache->info_index = (index + 1) % PCACHE_META_INDEX_MAX;
-
+ if (cache_info_addr) {
if (opts->data_crc !=
(cache->cache_info.flags &
PCACHE_CACHE_FLAGS_DATA_CRC)) {
pcache_dev_err(pcache, "invalid option for
data_crc: %s, expected: %s",
@@ -56,6 +51,8 @@ static int cache_info_init(struct pcache_cache *cache,
struct pcache_cache_optio
return -EINVAL;
}
+ cache->info_index = ((char *)cache_info_addr - (char
*)cache->cache_info_addr) / PCACHE_CACHE_INFO_SIZE;
+
return 0;
}
diff --git a/drivers/md/dm-pcache/cache_segment.c
b/drivers/md/dm-pcache/cache_segment.c
index 0b4bb08011ce..0a0016702ce7 100644
--- a/drivers/md/dm-pcache/cache_segment.c
+++ b/drivers/md/dm-pcache/cache_segment.c
@@ -60,7 +60,6 @@ static int cache_seg_info_load(struct
pcache_cache_segment *cache_seg)
cache_seg->info_index =
((char *)cache_seg_info_addr - (char
*)cache_seg_info_addr_base) /
PCACHE_SEG_INFO_SIZE;
- cache_seg->info_index = (cache_seg->info_index + 1) %
PCACHE_META_INDEX_MAX;
out:
mutex_unlock(&cache_seg->info_lock);
在 12/2/2025 8:11 PM, Li Chen 写道:
From: Li Chen <[email protected]>
dm-pcache stores metadata (cache_info and segment_info) in 4K-aligned
slots on the cache device, using sequence numbers and CRC to identify
the latest valid copy.
However, the cache_info and segment_info paths were computing their
on-media index using sizeof(struct) instead of the 4K metadata stride.
As a result:
* cache_info updates (including gc_percent set via a dmsetup message)
were written to invalid offsets between metadata slots and failed
to persist across table reloads or reboots.
* segment_info indexing became desynchronized, so rotation to the
"next" slot no longer matched the location returned by
pcache_meta_find_latest().
The issue can be reproduced with:
dmsetup create pcache_vdb --table \
"0 $(blockdev --getsz /dev/vdb) pcache /dev/pmem0 /dev/vdb 4 \
cache_mode writeback data_crc false"
# Check default gc_percent (70)
dmsetup status pcache_vdb
# Change gc_percent to 10
dmsetup message pcache_vdb 0 "gc_percent 10"
# Verify change is active in memory
dmsetup status pcache_vdb
# Reboot the system...
# Without patch (gc_percent reverts to 70):
dmsetup status pcache_vdb
# With patch (gc_percent persists as 10):
dmsetup status pcache_vdb
This series fixes the issue by deriving the metadata slot index from
the pointer returned by pcache_meta_find_latest(), using the 4K stride
(CACHE_INFO_SIZE / SEG_INFO_SIZE). This ensures that updates to
cache_info and segment_info are written to valid slots and remain
consistent with the on-media layout.
Li Chen (2):
dm pcache: fix cache info indexing
dm pcache: fix segment info indexing
drivers/md/dm-pcache/cache.c | 13 ++++++++++---
drivers/md/dm-pcache/cache_segment.c | 6 +++++-
2 files changed, 15 insertions(+), 4 deletions(-)
