From mboxrd@z Thu Jan 1 00:00:00 1970 From: Loic Dachary Subject: Reducing backfilling/recovery long tail Date: Fri, 12 Dec 2014 16:16:34 +0100 Message-ID: <548B06D2.90609@dachary.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="fJM1wkJ55O3BfkcpLi2pt4htGk5HlKsEV" Return-path: Received: from mail2.dachary.org ([91.121.57.175]:52024 "EHLO smtp.dmail.dachary.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S933263AbaLLPQg (ORCPT ); Fri, 12 Dec 2014 10:16:36 -0500 Sender: ceph-devel-owner@vger.kernel.org List-ID: To: Samuel Just , Sage Weil Cc: Ceph Development This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --fJM1wkJ55O3BfkcpLi2pt4htGk5HlKsEV Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Hi Sam & Sage, In the context of http://tracker.ceph.com/issues/9566 I'm inclined to thi= nk the best solution would be that the AsyncReserver choose a PG instead = of just picking the next one in the list when there is a free slot. It wo= uld always choose a PG that must move to/from an OSDs for which there are= more PGs waiting in the AsyncRerserver than any other OSD. The sort invo= lved does not seem too expensive. Calculating priorities before adding the PG to the AsyncReserver seems wr= ong because the state of the system will change significantly while the P= G is waiting to be processed. For instance the first PGs to be added have= a low priority while the next have increasing priorities when they accum= ulate. If reservations are canceled because the OSD map changed again (ma= ybe another OSD is decommissioned before recovery of the first one comple= tes), you may end up having high priorities for PGs that are no longer as= sociated with busy OSDs. That could backfire and create even more frequen= t long tails. What do you think ? Cheers --=20 Lo=C3=AFc Dachary, Artisan Logiciel Libre --fJM1wkJ55O3BfkcpLi2pt4htGk5HlKsEV Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iEYEARECAAYFAlSLBtIACgkQ8dLMyEl6F221LwCghsacQQ4idxQ1XExG+rJy5UQp JcEAnj2bYKP0l9Mxbc3VTn4yQqvtRJfA =2BsI -----END PGP SIGNATURE----- --fJM1wkJ55O3BfkcpLi2pt4htGk5HlKsEV--