On Tue, 24 Jun 2025, Dongsheng Yang wrote: > Hi Mikulas, > This is V1 for dm-pcache, please take a look. > > Code: > https://github.com/DataTravelGuide/linux tags/pcache_v1 > > Changelogs from RFC-V2: > - use crc32c to replace crc32 > - only retry pcache_req when cache full, add pcache_req into defer_list, > and wait cache invalidation happen. > - new format for pcache table, it is more easily extended with > new parameters later. > - remove __packed. > - use spin_lock_irq in req_complete_fn to replace > spin_lock_irqsave. > - fix bug in backing_dev_bio_end with spin_lock_irqsave. > - queue_work() inside spinlock. > - introduce inline_bvecs in backing_dev_req. > - use kmalloc_array for bvecs allocation. > - calculate ->off with dm_target_offset() before use it. Hi The out-of-memory handling still doesn't seem right. If the GFP_NOWAIT allocation doesn't succeed (which may happen anytime, for example it happens when the machine is receiving network packets faster than the swapper is able to swap out data), create_cache_miss_req returns NULL, the caller changes it to -ENOMEM, cache_read returns -ENOMEM, -ENOMEM is propagated up to end_req and end_req will set the status to BLK_STS_RESOURCE. So, it may randomly fail I/Os with an error. Properly, you should use mempools. The mempool allocation will wait until some other process frees data into the mempool. If you need to allocate memory inside a spinlock, you can't do it reliably (because you can't sleep inside a spinlock and non-sleepng memory allocation may fail anytime). So, in this case, you should drop the spinlock, allocate the memory from a mempool with GFP_NOIO and jump back to grab the spinlock - and now you holding the allocated object, so you can use it while you hold the spinlock. Another comment: set_bit/clear_bit use atomic instructions which are slow. As you already hold a spinlock when calling them, you don't need the atomicity, so you can replace them with __set_bit and __clear_bit. Mikulas
