Date: Mon, 7 Jun 1999 17:40:20 -0400 (EDT) From: Zhihui Zhang <zzhang@cs.binghamton.edu> To: freebsd-hackers@FreeBSD.ORG Subject: Re: help with I/O optimization with object Message-ID: <Pine.GSO.3.96.990607173609.13033A-100000@sol.cs.binghamton.edu> In-Reply-To: <Pine.GSO.3.96.990607141929.12278A-100000@sol.cs.binghamton.edu>
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On Mon, 7 Jun 1999, Zhihui Zhang wrote: > > While studying the file ufs_readwrite.c, I see routines like uiomoveco() > that calls vm_uiomove() in vm_map.c. I am almost sure that these are new > in FreeBSD 3.x. The comment in ffs_read() says "not a VM based I/O > requests" == "not headed for the buffer cache". This does not make sense > to me although I understand something about VMIO buffers and non-VMIO > buffers. I hope someone can explain the basic ideas of I/O optimization > with VM object (relating to the OBJ_OPT flag and the global variable > vfs_ioopt) so that I can understand the code easier. > After searching the mailing list archive for some time and tracing down who calls vm_uiomove(), it seems to me that this is the zero copy read stuff used to read data into the current process' address space. However, I do not know when it can be useful or any more details. -Zhihui To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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