Date: Fri, 13 Nov 2020 23:14:07 -0500 From: Alexander Motin <mav@FreeBSD.org> To: "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: MAXPHYS bump for FreeBSD 13 Message-ID: <1bff381f-3d6e-b20c-28f9-1403a9dfe0f6@FreeBSD.org>
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> We currently have a MAXPHYS of 128k. This is the maximum size of I/Os > that we normally use (though there are exceptions). > > I'd like to propose that we bump MAXPHYS to 1MB, as well as bumping > DFLTPHYS to 1MB. I am all for the MAXPHYS change, as Warner told it was my proposition on a chat. ZFS uses blocks and aggregates I/O up to 1MB already and can more potentially, and having I/O size lower then this just overflows disk queues, increases processing overheads, complicates scheduling and in some cases causes starvation. I'd just like to note that DFLTPHYS should probably not be changed that straight (if at all), since it is used as a fallback for legacy code. If it is used for anything else -- that should be reviewed and probably migrated to some other constant(s). -- Alexander Motin
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