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Merged
yangdongsheng merged 2 commits into from
Aug 12, 2025
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Add pcache v5 summary #4

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d71e19f
Fill in mail and code for pcache v5
yangdongsheng Aug 12, 2025
b5e7e32
link pcache v5 cover letter
yangdongsheng Aug 12, 2025
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1 change: 1 addition & 0 deletions pcache/pcache_index.md
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Expand Up @@ -7,3 +7,4 @@ layout: default
- [PCache RFC](pcache_RFC.md)
- [PCache RFC V2](pcache_RFC_V2.md)
- [PCache v4](pcache_v4.md)
- [PCache v5](pcache_v5.md)
53 changes: 53 additions & 0 deletions pcache/pcache_v5.md
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# PCache v5

This document summarizes **dm-pcache** patch set v5. It is based on v6.16 of
the Linux kernel and contains the latest updates and testing results for the
persistent cache target.

## Mail
> Hi Mikulas,
> This is V5 for dm-pcache, please consider merging.
>
> As you requested, I've squashed these patches into a single patch based on
> v6.16. If anything needs tweaking while merging, feel free to modify it
> directly. I can also send a rebased version on top of the linux-dm branch if
> you prefer.
>
> This patch has been tested extensively. Once it's merged into linux-dm I'll
> keep running ongoing tests against dm-6.18.

[Full cover letter on dm-devel](https://marc.info/?l=dm-devel&m=175498716132537)

## Code
https://github.com/DataTravelGuide/linux/tree/pcache_v5

## Changelog

### V5 from V4
- Fix `get_n_vecs()` bug when the buffer is not page‑aligned; use
`bio_add_max_vecs()` instead.
- Use `kvcalloc()` for allocations larger than 32,768 bytes.
- For mempool allocations, try `GFP_NOWAIT` first and fall back to
`GFP_NOIO`.

## Testing
The following tests were executed against dm-pcache v5:

1. **dtg-tests for pcache** – includes dmsetup operations, failslab,
fault injection (`fail_make_request`) and backing device delay tests,
plus xfstests (`generic/rw`) under various parameters.
2. **Striped pmem as cache device** – dtg-tests suite executed with a
striped pmem configuration.
3. **KASAN and memleak modes** – all of the above tests run with KASAN
and memory leak detection enabled.
4. **gcov coverage** – reported 100% function coverage and 90%+ line
coverage; remaining uncovered code includes `BUG()` lines and
difficult‑to‑reach error paths. The `mempool_alloc` path with
`GFP_NOIO` was exercised.

## Results
- [dtg-tests (virtio)](https://datatravelguide.github.io/dtg-blog/pcache/pcache_v5_result_virtio/results.html)
- [dtg-tests (striped pmem)](https://datatravelguide.github.io/dtg-blog/pcache/pcache_v5_result_ram/results.html)
- [KASAN & memleak tests](https://datatravelguide.github.io/dtg-blog/pcache/pcache_v5_result_kasan/results.html)
- [Coverage report](https://datatravelguide.github.io/dtg-blog/pcache/pcache_cov_v5/dm-pcache/index.html)

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