casaroli opened a new pull request, #20629:
URL: https://github.com/apache/nuttx/pull/20629
## Summary
When a range of granules is not free, `gran_match()` gives `gran_search()` a
position to continue from. Since commit 1abcb6a0905 it reads the whole GAT cell
again for this and uses the highest used bit of the cell, not of the range. A
used bit above the range moves the search past all of the free granules below
it.
Example: a cell with only bits 0 and 31 used is never searched again. In a
page pool under load, `gran_alloc()` for one page returned NULL with about
34000 pages free.
This PR uses the masked cell value again, as before commit 1abcb6a0905.
## Impact
`mm_gran` (`gran_alloc()`, and the page allocator of `CONFIG_MM_PGALLOC`).
Allocations that failed with free granules available now succeed. No API change.
## Testing
Host test: `mm/mm_gran/mm_grantable.c` compiled on Linux (Docker) and
compared with a brute-force search on 200000 random GAT tables and some fixed
cases.
```
master: gran_search(1) = -12, expect 1 FAIL
gran_search(17) = -12, expect 37 FAIL
FAILED (33942 failures)
this PR: PASSED (0 failures)
```
Build: `qemu-armv8a:nsh` and `qemu-armv8a:knsh`.
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