Date: Tue, 8 Dec 2015 12:19:11 -0700 From: Warner Losh <imp@bsdimp.com> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Dag-Erling Sm??rgrav <des@des.no>, "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org> Subject: Re: DELETE support in the VOP_STRATEGY(9)? Message-ID: <0A599E1F-FF63-4F21-B765-44A4531968DB@bsdimp.com> In-Reply-To: <20151208190622.GE82577@kib.kiev.ua> References: <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> <86wpsord9l.fsf@desk.des.no> <20151208185818.GD82577@kib.kiev.ua> <20151208190622.GE82577@kib.kiev.ua>
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--Apple-Mail=_BC57BC0A-AA3E-464E-BE53-94B0B1DD300A Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 > On Dec 8, 2015, at 12:06 PM, Konstantin Belousov <kostikbel@gmail.com> = wrote: >=20 > On Tue, Dec 08, 2015 at 08:58:18PM +0200, Konstantin Belousov wrote: >> On Tue, Dec 08, 2015 at 07:44:38PM +0100, Dag-Erling Sm??rgrav wrote: >>> Warner Losh <imp@bsdimp.com> writes: >>>> Dag-Erling Sm??rgrav <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. >>>=20 >>> 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). >> I again agree. This is how UFS issues TRIM. When the data block is = freed >> and there are no dandling pointers in the inode copy on disk pointing = to >> the block, BIO_DELETE is issued if volume reports it. Everything = else >> is up to the geom stack and driver. > I am sorry for the followup mail, but I probably have to explain more. > The freed block, for which BIO_DELETE is issued, is not marked as free > in the bitmap, until the BIO_DELETE completion is reported. In other > words, we do not reuse the freed block while TRIM command is possibly > executed. Since the BIO_DELETE queue up in the storage layer, and we make no = requirement on ordering[*] in the storage layer, this is prudent. A BIO_WRITE could = overtake the BIO_DELETE, which would be bad. Warner [*] Well, apart from BIO_ORDERED which isn=E2=80=99t used for BIO_DELETE = requests and generally is only needed in FreeBSD to ensure that writes are = flushed out (with BIO_FLUSH) in a particular order for power-fail recovery. --Apple-Mail=_BC57BC0A-AA3E-464E-BE53-94B0B1DD300A Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc Content-Description: Message signed with OpenPGP using GPGMail -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQIcBAEBCgAGBQJWZy0wAAoJEGwc0Sh9sBEAbJEQAIC1gd3LTznddZhgW+zwheyV JPaStJjcQCHUSb3DRzs+s+r7nMqMmUCSzqTUZEIwVEet8MT3lhUt8vQ+V7eC8EjF pGihuaVXPfqSMBZA9wl4OG1R4szXbNVNtz56ZmZpWXLnLdTwoVdR0Qbbqg5KbtXm cRdYRyAfEP8RJ7FeTB8rmYjsAFrm93R9oqI5415j8jX/eIOUjpsZJOVKmJzNSAMZ DtYMTUtMrx/UHi97PEnh4DhUs8O2D/jGjIke3khQtsLc4oluizMlkuxSq+fOH7sc NOS1pHwSFrj8OK6hh5MrLytHqXYecnouKMSWylyTp0gPsA0QZ+4ua5uJYh0oyWqo w1RjUqTUQQxGQeK61F7/s1cTn2GgR2GyNIWB/XTdn8rUbDZU8439j742Vz7jc8XQ +kQD6SA2H/+7WM0VjvZ/E0EPSIYAu5r4MhwE7xd38HOsfTukBiLUGCELPdqyAlqI rWEQAt7Jbfndi7w6z6lnbIEg7t1tifmXRVgWVMmHBf3hMJD28LdmGBdLYRjACy+e +qg+entLA9sLK2PCv4wZOqCsTiSfM7dLIW+6i4Urau9yfoLhFBpH0d7AcXZTug/D mWxcbW/6DSqBWBXtedpGPnSi5/vv4MD47p9bf3zq1a0s5dALfmm4bgg8/Y/kUreY qlXgGo12PmihfIoLgYNt =qcyS -----END PGP SIGNATURE----- --Apple-Mail=_BC57BC0A-AA3E-464E-BE53-94B0B1DD300A--
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