Date: Wed, 2 Feb 2022 11:05:17 +0200 From: Andriy Gapon <avg@FreeBSD.org> To: Warner Losh <imp@bsdimp.com>, Peter Jeremy <peterj@freebsd.org> Cc: Konstantin Belousov <kostikbel@gmail.com>, FreeBSD FS <freebsd-fs@freebsd.org>, "freebsd-geom@FreeBSD.org" <freebsd-geom@freebsd.org> Subject: Re: bio re-ordering Message-ID: <b75872f4-521b-5eab-68d0-4b1c04a10add@FreeBSD.org> In-Reply-To: <CANCZdfqBQOvzMCrJxWq9GzqCKyK_AubBE1CxAW5FULnE7D_jrg@mail.gmail.com> References: <YfTCs7j3TPZFcFCD@server.rulingia.com> <YfTEj1KLhQhoR3xP@kib.kiev.ua> <CANCZdfoqQ3Ze%2BcMTsk_ho9x8hsSM9=fTavSao%2BUtwc2nSAEJpQ@mail.gmail.com> <Yfo3i9Yy/uCUpss1@server.rulingia.com> <CANCZdfqBQOvzMCrJxWq9GzqCKyK_AubBE1CxAW5FULnE7D_jrg@mail.gmail.com>
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On 02/02/2022 09:58, Warner Losh wrote: > > > On Wed, Feb 2, 2022, 12:49 AM Peter Jeremy <peterj@freebsd.org > <mailto:peterj@freebsd.org>> wrote: > > Thanks all for the very prompt responses. > > On 2022-Jan-28 22:32:02 -0700, Warner Losh <imp@bsdimp.com > <mailto:imp@bsdimp.com>> wrote: > >I think that ufs relies on two ordering primitives, both marked with > >BIO_ORDERED today. > >That's what most of the drivers key off of. We always set BIO_ORDERED on > >all the BIO_FLUSH > >events as far as I Can tell. > > Thanks for that warning. I don't think geom_gate understands either > B_BARRIER or BIO_ORDERED. I shall have a closer look. > > > It needs to understand BIO_ORDERED. > > > >to it. b*barrierwrite() sets this, and that's used in the ffs_alloc code. > > In my case, I'm interested in ZFS, rather than UFS and it doesn't seem > to set B_BARRIER or BIO_ORDERED or indirectly. > > > I went hunting ZFS for this year's ago and in the pre OpenZFS code they were > used, but there were three layers of indirection that obscured it. ZFS doesn't > use the buffer cache, so B_BARRIER isn't relevant. I'll see if I can find it > with the new code. > > But if it never sets BIO_ORDERED, drivers are already reordering things. That's > all any other driver in the tree worries about... Hmm... it looks like both the old and new (Open)ZFS use BIO_FLUSH command without BIO_ORDERED flag. Not sure if it happens to do the right thing anyway or not. -- Andriy Gapon
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