Date: Tue, 08 Dec 2015 19:44:38 +0100 From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no> To: Warner Losh <imp@bsdimp.com> Cc: "freebsd-hackers\@freebsd.org" <freebsd-hackers@freebsd.org> Subject: Re: Fwd: DELETE support in the VOP_STRATEGY(9)? Message-ID: <86wpsord9l.fsf@desk.des.no> In-Reply-To: <CANCZdfoXdcD%2B9jeVR1Np16gafBf0_4B2wombwxze8DvJwf7cMg@mail.gmail.com> (Warner Losh's message of "Tue, 8 Dec 2015 10:07:42 -0700") References: <CAH7qZftSVAYPmxNCQy=VVRj79AW7z9ade-0iogv2COfo2x%2Ba2Q@mail.gmail.com> <201512052002.tB5K2ZEA026540@chez.mckusick.com> <CAH7qZfs6ksE%2BQTMFFLYxY0PNE4hzn=D5skzQ91=gGK2xvndkfw@mail.gmail.com> <86poyhqsdh.fsf@desk.des.no> <CAH7qZftVj9m_yob=AbAQA7fh8yG-VLgM7H0skW3eX_S%2Bv75E-g@mail.gmail.com> <86fuzdqjwn.fsf@desk.des.no> <CANCZdfo=NfKy51%2B64-F_v%2BDh2wkrFYP4gXe=X9RWSSao49gO9g@mail.gmail.com> <CANCZdfqHoduhdCss0b6=UsBPAxfRZv4hF8vyuUVLBdP5gYUduQ@mail.gmail.com> <864mfssxgt.fsf@desk.des.no> <CANCZdfoXdcD%2B9jeVR1Np16gafBf0_4B2wombwxze8DvJwf7cMg@mail.gmail.com>
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Warner Losh <imp@bsdimp.com> writes: > Dag-Erling Sm=C3=B8rgrav <des@des.no> writes: > > But the filesystem does not know whether the underlying storage is > > electromechanical or solid-state, nor does it know whether the user > > cares much about seek times (unless we introduce the heuristic > > "avoid creating holes unless the file already has them, in which > > case the userland probably does not care"). > Actually, the filesystem does know. Or has some knowledge of what > is supported and what isn't. BIO_DELETE support is a strong indicator > of a flash or other log-type system. The filesystem can ask the layer below if BIO_DELETE is supported, but should not assume anything about what it means. For instance, I could write a gnop-like module that translates BIO_DELETE into an all-zeroes BIO_WRITE and passes everything else unmodified. It would provide a stronger guarantee than, say, SATA TRIM but would also have a completely different performance profile (even on SSDs, since it would do its work synchronously whereas TRIM works asynchronously). Anyway, my point is that Maxim needs to revise his assumptions. DES --=20 Dag-Erling Sm=C3=B8rgrav - des@des.no
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