On Mon, 7 Jul 2025, Dongsheng Yang wrote:
> Hi Mikulas,
> This is V2 for dm-pcache, please take a look.
>
> Code:
> https://github.com/DataTravelGuide/linux tags/pcache_v2
>
> Changelogs
>
> V2 from V1:
> - introduce req_alloc() and req_init() in backing_dev.c, then we
> can do req_alloc() before holding spinlock and do req_init()
> in subtree_walk().
> - introduce pre_alloc_key and pre_alloc_req in walk_ctx, that
> means we can pre-allocate cache_key or backing_dev_request
> before subtree walking.
> - use mempool_alloc() with NOIO for the allocation of cache_key
> and backing_dev_req.
> - some coding style changes from comments of Jonathan.
Hi
mempool_alloc with GFP_NOIO never fails - so you don't have to check the
returned value for NULL and propagate the error upwards.
"backing_req->kmem.bvecs = kmalloc_array(n_vecs, sizeof(struct bio_vec),
GFP_NOIO)" - this call may fail and you should handle the error gracefully
(i.e. don't end the bio with an error). Would it be possible to trim the
request to BACKING_DEV_REQ_INLINE_BVECS vectors and retry it?
Alternativelly, you can create a mempool for the largest possible n_vecs
and allocate from this mempool if kmalloc_array fails.
I'm sending two patches for dm-pcache - the first patch adds the include
file linux/bitfield.h - it is needed in my config. The second patch makes
slab caches per-module rather than per-device, if you have them
per-device, there are warnings about duplicate cache names.
BTW. What kind of persistent memory do you use? (afaik Intel killed the
Optane products and I don't know of any replacement)
Some times ago I created a filesystem for persistent memory - see
git://leontynka.twibright.com/nvfs.git - I'd be interested if you can test
it on your persistent memory implementation.
Mikulas