Date: Sat, 15 Feb 2003 19:25:27 -0600 From: "Alan L. Cox" <alc@imimic.com> To: arch@freebsd.org Cc: trb@freebsd.org Subject: TRB resolution of M_* changes to the memory and mbuf allocators Message-ID: <3E4EE887.73508A59@imimic.com>
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The TRB reviewed the change to the memory and mbuf allocators that removes the M_*WAIT* flags and replaces all occurrences in the source code with 0. Those in favor argued the change would: o eliminate typographic errors, o emphasize that these APIs have a default behavior (wait for operation to complete) with only exceptional cases marked by a flag argument, and o emphasize to developers that synchronization issues cannot be solved simply by making allocation requests non-blocking. Those opposed to the change argued: o this breaks source-code compatibility with prior releases of FreeBSD as well as other systems with the same APIs (e.g. netbsd, openbsd), o typographic errors of the sort described are better handled by defining names with unique non-zero values that can then be validated in the routines where they are passed as parameters, o the allocators have not historically had a default behaviour, o removing the explicit specification of whether to wait or not wait at each call site removes useful information from the source code, and o the synchronization issues intended to be addressed will not be solved in this way but instead require developer education. After careful review of arguments from both sides the TRB voted: In favor of change: 0 Opposed to change: 9 Abstain: 0 It is the TRB's decision that this change should be reverted; and instead the course of action outlined below should be followed. 1) Revert to the old API 2) Put enforcement into malloc/mbuf so that you have to specify a flag. 2a)with the default being NOWAIT/WAITOK if you don't for a transition period. 3) Put witness checks in malloc for "sleepability." 4) Make all the M_* flags unique to avoid possible misuse. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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