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For the "struct tcmu_cmd_entry" in cmd area, the minimum size will be sizeof(struct tcmu_cmd_entry) == 112 Bytes. And it could fill about (sizeof(struct rsp) - sizeof(struct req)) / sizeof(struct iovec) == 68 / 16 ~= 4 data regions(iov[4]) by default. For most tcmu_cmds, the data block indexes allocated from the data area will be continuous. And for the continuous blocks they will be merged into the same region using only one iovec. For the current code, it will always allocates the same number of iovecs with blocks for each tcmu_cmd, and it will wastes much memories. For example, when the block size is 4K and the DATA_OUT buffer size is 64K, and the regions needed is less than 5(on my environment is almost 99.7%). The current code will allocate about 16 iovecs, and there will be (16 - 4) * sizeof(struct iovec) = 192 Bytes cmd area memories wasted. Here adds two helpers to calculate the base size and full size of the tcmu_cmd. And will recalculate them again when it make sure how many iovs is needed before insert it to cmd area. Signed-off-by: Xiubo Li <lixiubo@cmss.chinamobile.com> Acked-by: Mike Christie <mchristi@redhat.com> Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.