tcmu: Add global data block pool support
For each target there will be one ring, when the target number grows larger and larger, it could eventually runs out of the system memories. In this patch for each target ring, currently for the cmd area the size will be fixed to 8MB and for the data area the size will grow from 0 to max 256K * PAGE_SIZE(1G for 4K page size). For all the targets' data areas, they will get empty blocks from the "global data block pool", which has limited to 512K * PAGE_SIZE(2G for 4K page size) for now. When the "global data block pool" has been used up, then any target could wake up the unmap thread routine to shrink other targets' data area memories. And the unmap thread routine will always try to truncate the ring vma from the last using block offset. When user space has touched the data blocks out of tcmu_cmd iov[], the tcmu_page_fault() will try to return one zeroed blocks. Here we move the timeout's tcmu_handle_completions() into unmap thread routine, that's to say when the timeout fired, it will only do the tcmu_check_expired_cmd() and then wake up the unmap thread to do the completions() and then try to shrink its idle memories. Then the cmdr_lock could be a mutex and could simplify this patch because the unmap_mapping_range() or zap_* may go to sleep. Signed-off-by: Xiubo Li <lixiubo@cmss.chinamobile.com> Signed-off-by: Jianfei Hu <hujianfei@cmss.chinamobile.com> Acked-by: Mike Christie <mchristi@redhat.com> Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
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