Comments on: Re: vmsplice() + SPLICE_F_GIFT flag ?? http://coder.cl/2009/08/re-vmsplice-splice_f_gift-flag/ web developer & system programmer Sat, 04 Feb 2012 22:00:50 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: Daniel Molina Wegener http://coder.cl/2009/08/re-vmsplice-splice_f_gift-flag/comment-page-1/#comment-1455 Daniel Molina Wegener Fri, 12 Mar 2010 18:26:05 +0000 http://coder.cl/?p=104#comment-1455 Thank you very much Carsten. I will communicate it to Eduardo. Best Regards, D Thank you very much Carsten. I will communicate it to Eduardo.

Best Regards,
D

]]> By: Carsten Milkau http://coder.cl/2009/08/re-vmsplice-splice_f_gift-flag/comment-page-1/#comment-1454 Carsten Milkau Fri, 12 Mar 2010 17:22:14 +0000 http://coder.cl/?p=104#comment-1454 Note that for using SPLICE_F_GIFT, the chunks must be <em>page</em> aligned, i. e. every chunk must be a contiguous block of full pages. Page size normally is 4 KiB (0x1000 in Hex). So, the following example is properly page aligned: iovec[0]->io_base==0×080ed000, iovec[0]->io_len==0×1000, iovec[1]->io_base==0×080ef000, iovec[1]->io_len==0×2000, iovec[2]->io_base==0×080f4000, iovec[2]->io_len==0×1000, note that the chunks have different sizes, but all of them multiples of the page size (0x1000). Also, there is a 12 KiB gap between the second and the last chunk, but all chunks start at a page-aligned address (last three hexdigits are zero). Compare instead the following example: iovec[0]->io_base==0×080ed000, iovec[0]->io_len==0×400, iovec[1]->io_base==0×080ed400, iovec[1]->io_len==0×400, iovec[2]->io_base==0×080fd800, iovec[2]->io_len==0×400, iovec[2]->io_base==0×080fdc00, iovec[2]->io_len==0×400, All four chunks from a contiguous range of 4 KiB, and each one is 1 KiB in length. Also, the first block is page-aligned, so that the four chunks together represent exactly one page in virtual memory. However, the <em>individual</em> chunks are <em>not</em> properly page-aligned: iovec[0] does not end on a page boundary, iovec[3] does not begin on a page boundary, and iovec[1] and iovec[2] do neither begin nor end on a page boundary. <b>In short: every chunk must begin and end on a page boundary (hex address ending on 000).</b> Note that for using SPLICE_F_GIFT, the chunks must be page aligned, i. e. every chunk must be a contiguous block of full pages. Page size normally is 4 KiB (0×1000 in Hex). So, the following example is properly page aligned:

iovec[0]->io_base==0×080ed000, iovec[0]->io_len==0×1000,
iovec[1]->io_base==0×080ef000,
iovec[1]->io_len==0×2000,
iovec[2]->io_base==0×080f4000, iovec[2]->io_len==0×1000,

note that the chunks have different sizes, but all of them multiples of the page size (0×1000). Also, there is a 12 KiB gap between the second and the last chunk, but all chunks start at a page-aligned address (last three hexdigits are zero).

Compare instead the following example:

iovec[0]->io_base==0×080ed000, iovec[0]->io_len==0×400,
iovec[1]->io_base==0×080ed400,
iovec[1]->io_len==0×400,
iovec[2]->io_base==0×080fd800, iovec[2]->io_len==0×400,
iovec[2]->io_base==0×080fdc00, iovec[2]->io_len==0×400,

All four chunks from a contiguous range of 4 KiB, and each one is 1 KiB in length. Also, the first block is page-aligned, so that the four chunks together represent exactly one page in virtual memory. However, the individual chunks are not properly page-aligned: iovec[0] does not end on a page boundary, iovec[3] does not begin on a page boundary, and iovec[1] and iovec[2] do neither begin nor end on a page boundary.

In short: every chunk must begin and end on a page boundary (hex address ending on 000).

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