Date: Sun, 19 Aug 2007 00:07:56 +0200 From: Pawel Jakub Dawidek <pjd@FreeBSD.org> To: freebsd-arch@FreeBSD.org Subject: Re: Lockless uidinfo. Message-ID: <20070818220756.GH6498@garage.freebsd.pl> In-Reply-To: <20070818120056.GA6498@garage.freebsd.pl> References: <20070818120056.GA6498@garage.freebsd.pl>
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--gKijDXBCEH69PxaN Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Two more things... > The patch below remove per-uidinfo locks: >=20 > http://people.freebsd.org/~pjd/patches/uidinfo_lockless.patch We could upgrade from lock-free algorithm I used here to wait-free algorithm, but we don't have atomic_fetchadd_long(). How hard will it be to implement it? We could then change: do { old =3D uip->ui_proccnt; if (old + diff > max) return (0); } while (atomic_cmpset_long(&uip->ui_proccnt, old, old + diff) =3D=3D 0); to something like this: if (atomic_fetchadd_long(&uip->ui_proccnt, diff) + diff > max) { atomic_subtract_long(&uip->ui_proccnt, diff); return (0); } > I needed to change ui_sbsize from rlim_t (64bit) to long, because we > don't have 64bit atomics on all archs, and because sbsize represents > size in bytes, it can't go beyond 32bit on 32bit archs (PAE might be a > bit of a problem). Currently it's not a problem, because socket buffers have to be mapped in kernel space, so we can't map more than 4GB. This might be eventually a problem if we implement unmapped socket buffers and ui_sbsize will be sum of socket buffers from many processes. --=20 Pawel Jakub Dawidek http://www.wheel.pl pjd@FreeBSD.org http://www.FreeBSD.org FreeBSD committer Am I Evil? Yes, I Am! --gKijDXBCEH69PxaN Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.4 (FreeBSD) iD8DBQFGx228ForvXbEpPzQRAj+QAJ9Y4g6hqHOfEhndF71nVdz5e36KRwCgnJPM R3JbjJEwLidFJy9fJ9FGzP0= =yQ2d -----END PGP SIGNATURE----- --gKijDXBCEH69PxaN--
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