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bmap: Enabled at least opportunistic bmap allocations

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This doesn't fully replace the lookahead buffer, but at least augments
it with known bmap state when available.

To be honest, this is a minimal effort hack to try to get something
benchmarkable without dealing with all the catch-22 issues that a
self-support bmap allocator would encounter (allocating blocks for the
bmap requires a bmap, oh no).

Though now that I'm writing this, maybe this is a reasonable long-term
solution? Having the lookahead buffer to fall back on solves a lot of
problems, and, realistically, it's unlikely to be a performance
bottleneck unless the user has extreme write requests (>available
storage?).

---

Also tweaked field naming to be consistent between the bmap and
lookahead buffer.
This commit is contained in:
Christopher Haster
2025-07-28 01:11:48 -05:00
parent 838a4beee1
commit 71b9ad2412
4 changed files with 172 additions and 97 deletions
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lfs3.h
+7 -4
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@@ -843,8 +843,8 @@ typedef struct lfs3_grm {
} lfs3_grm_t;
// gbmap encoding:
// .---+- -+- -+- -+- -. cursor: 1 leb128 <=5 bytes
// | cursor | known: 1 leb128 <=5 bytes
// .---+- -+- -+- -+- -. window: 1 leb128 <=5 bytes
// | window | known: 1 leb128 <=5 bytes
// +---+- -+- -+- -+- -+ block: 1 leb128 <=5 bytes
// | known | trunk: 1 leb128 <=4 bytes
// +---+- -+- -+- -+- -+ cksum: 1 le32 4 bytes
@@ -857,7 +857,7 @@ typedef struct lfs3_grm {
#define LFS3_GBMAP_DSIZE (5+5+5+4+4)
typedef struct lfs3_gbmap {
lfs3_block_t cursor;
lfs3_block_t window;
lfs3_block_t known;
lfs3_btree_t b;
} lfs3_gbmap_t;
@@ -916,8 +916,11 @@ typedef struct lfs3 {
struct lfs3_lookahead {
lfs3_block_t window;
lfs3_block_t off;
lfs3_block_t size;
lfs3_block_t known;
lfs3_block_t ckpoint;
#ifdef LFS3_BMAP
lfs3_block_t bmapped;
#endif
uint8_t *buffer;
} lookahead;
#endif