The use of kmap() is being deprecated in favor of kmap_local_page(). There are two main problems with kmap(): (1) It comes with an overhead as the mapping space is restricted and protected by a global lock for synchronization and (2) it also requires global TLB invalidation when the kmap’s pool wraps and it might block when the mapping space is fully utilized until a slot becomes available. With kmap_local_page() the mappings are per thread, CPU local, can take page faults, and can be called from any context (including interrupts). It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore, the tasks can be preempted and, when they are scheduled to run again, the kernel virtual addresses are restored and still valid. Therefore, replace kmap() with kmap_local_page() in fuse_readdir_cached(), it being the only call site of kmap() currently left in fs/fuse.
Unified · Split
| @@ -547,9 +547,9 @@ retry_locked: · 546 unmodified lines | ||
| 547 | 547 | * Contents of the page are now protected against changing by holding |
| 548 | 548 | * the page lock. |
| 549 | 549 | */ |
| 550 | − addr = kmap(page); | |
| 550 | + addr = kmap_local_page(page); | |
| 551 | 551 | res = fuse_parse_cache(ff, addr, size, ctx); |
| 552 | − kunmap(page); | |
| 552 | + kunmap_local(addr); | |
| 553 | 553 | unlock_page(page); |
| 554 | 554 | put_page(page); |
| 555 | 555 | |