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trv: Adopted LFS3_t_STALE for marking block queue as stale

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This solves the previous gc-needs-block-queue-so-we-can-clobber-block-
queue issue by adding an additional LFS3_t_STALE flag to indicate when
any block queues would be invalid.

So instead of clearing block queues in lfs3_alloc_ckpoint, we just set
LFS3_t_STALE, and any lfs3_trv_ts can clear their block queues in
lfs3_trv_read. This allows lfs3_mgc_ts to be allocated without a block
queue when doing any LFS3_M_*/LFS3_F_*/LFS3_GC_* work.

LFS3_t_STALE is set at the same time as LFS3_t_CKPOINT and LFS3_t_DIRTY,
but we need a separate bit so lfs3_trv_read can clear the flag after
flushing without losing ckpoint/dirty information.

---

Unfortunately, none of the stack-allocated lfs3_mgc_ts are on the stack
hot-path, so we don't immediate savings. But note the 2-words saved in
ctx when compiling in LFS3_GC mode:

                 code          stack          ctx
  before:       35940           2280          660
  after:        35944 (+0.0%)   2280 (+0.0%)  660 (+0.0%)

                 code          stack          ctx
  gbmap before: 38916           2296          772
  gbmap after:  38916 (+0.0%)   2296 (+0.0%)  772 (+0.0%)

                 code          stack          ctx
  gc before:    36012           2280          776
  gc after:     36016 (+0.0%)   2280 (+0.0%)  768 (-1.0%)
This commit is contained in:
Christopher Haster
2025-11-08 01:40:01 -06:00
parent d1d69c0a52
commit 14c369af93
4 changed files with 69 additions and 75 deletions
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lfs3.h
+4 -3
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@@ -340,9 +340,10 @@ enum lfs3_btype {
#define LFS3_t_TYPE 0xf0000000 // The traversal's type
#define LFS3_t_BTYPE 0x00f00000 // The current block type
#define LFS3_t_ZOMBIE 0x08000000 // File has been removed
#define LFS3_t_DIRTY 0x04000000 // Filesystem ckpointed outside traversal
#define LFS3_t_CKPOINTED \
0x02000000 // Filesystem ckpointed during traversal
0x04000000 // Filesystem ckpointed during traversal
#define LFS3_t_DIRTY 0x02000000 // Filesystem ckpointed outside traversal
#define LFS3_t_STALE 0x01000000 // Block queue probably out-of-date
// GC flags
#ifndef LFS3_RDONLY
@@ -1022,7 +1023,7 @@ typedef struct lfs3 {
// optional incremental gc state
#ifdef LFS3_GC
lfs3_trv_t gc;
lfs3_mgc_t gc;
#endif
} lfs3_t;