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Limited file->leaf to reads + erased-state caching

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This reverts most of the lazy-grafting/crystallization logic, but keeps
the general crystallization algorithm rewrite and file->leaf for caching
read operations and erased-state.

Unfortunately lazy-grafting/crystallization is both a code and stack
heavy feature for a relatively specific write pattern. It doesn't even
help if we're forced to write fragments due to prog alignment.

Dropping lazy-grafting/crystallization trades off linear write/rewrite
performance for code and stack savings:

                           code          stack          ctx
  before:                 37084           2304          636
  after:                  36428 (-1.8%)   2248 (-2.4%)  636 (+0.0%)

But with file->leaf we still keep the improvements to linear read
performance!

Compared to pre-file->leaf:

                           code          stack          ctx
  before file->leaf:      36016           2296          636
  after lazy file->leaf:  37084 (+3.0%)   2304 (+0.3%)  636 (+0.0%)
  after eager file->leaf: 36428 (+1.1%)   2248 (-2.1%)  636 (+0.0%)

I'm still on the fence about this, but lazy-grafting/crystallization is
just a lot of code... And the first 6 letters of littlefs don't spell
"speedy" last time I checked...

At the very least we can always add lazy-grafting/crystallization as an
opt-in write strategy later.
This commit is contained in:
Christopher Haster
2025-05-22 18:11:04 -05:00
parent 9c3a866508
commit 22c43124de
3 changed files with 60 additions and 233 deletions
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2
scripts/dbgflags.py
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@@ -44,8 +44,6 @@ FLAGS = [
('^', 'ORPHAN', 0x50000000, "Type = orphan" ),
('^', 'TRAVERSAL', 0x60000000, "Type = traversal" ),
('^', 'UNKNOWN', 0x70000000, "Type = unknown" ),
('o', 'UNCRYST', 0x00400000, "File's leaf not fully crystallized" ),
('o', 'UNGRAFT', 0x00800000, "File's leaf does not match bshrub/btree" ),
('o', 'UNFLUSH', 0x01000000, "File's data does not match disk" ),
('o', 'UNSYNC', 0x02000000, "File's metadata does not match disk" ),
('o', 'UNCREAT', 0x04000000, "File does not exist yet" ),