Date: Mon, 5 Mar 2007 21:30:22 +0200 From: Kostik Belousov <kostikbel@gmail.com> To: Yar Tikhiy <yar@comp.chem.msu.su> Cc: stable@freebsd.org Subject: Re: panic: kmem_malloc(16384): kmem_map too small: md-mounted /tmp filled up Message-ID: <20070305193022.GM10453@deviant.kiev.zoral.com.ua> In-Reply-To: <20070305191714.GF57253@comp.chem.msu.su> References: <20070227205351.GA72597@ravenloft.kiev.ua> <20070305035945.GA71660@xor.obsecurity.org> <20070305132350.GB57253@comp.chem.msu.su> <200703051314.29902@aldan> <20070305191714.GF57253@comp.chem.msu.su>
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--cy9Nn4fUvYST66Pl Content-Type: text/plain; charset=koi8-r Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Mar 05, 2007 at 10:17:14PM +0300, Yar Tikhiy wrote: > On Mon, Mar 05, 2007 at 01:14:29PM -0500, Mikhail Teterin wrote: > > On Monday 05 March 2007 08:23, Yar Tikhiy wrote: > > =3D > How will it break them? =9Aswap backing only touches swap if ther= e is > > =3D > memory pressure, i.e. precisely the situation in which malloc bac= king > > =3D > will panic. > > =3D=20 > > =3D I forgot that in BSD swap wouldn't be allocated in advance to its > > =3D consumers. =9AThen removing the -M flag and making swap backing the > > =3D default is a very sound choice. =9AThank you for correcting me. > >=20 > > Yar, would you change the man-page's advice and the default, then? >=20 > Yes, I'll be glad to if no objections arise until I finish updating > my CURRENT machine, i.e., tomorrow. :-) >=20 > > Someone still needs to look into the panic... Who would that be? >=20 > Obviously, Mr(s). Someone. :-) >=20 > The md case exposes a quite tangled nature of the problem. Funnily > enough, kernel malloc() cannot just fail in the case because it > must not fail if called with M_WAITOK. This means that the system > has quite a rough choice: >=20 > - put the requesting thread to sleep forever; > - grow kmem_map, eventually sacrifice all RAM to the greedy thread > and die sooner or later; > - panic immediately. >=20 > If all malloc() callers in the kernel were ready to deal with > allocation failure, the system could just tell the greedy thread > to buzz off. But too many kernel parts depend on malloc(M_WAITOK) > never failing. Perhaps it's the root of the problem. Mark callers that are ready for M_WAITOK failure with some additional flag, like M_FAILOK (feel free to propose meaningful name there). At least malloc()-based md could then use it. --cy9Nn4fUvYST66Pl Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (FreeBSD) iD8DBQFF7G/NC3+MBN1Mb4gRAuFeAJ4m4uHlhOSDkMNTNnVPKD2M+AOZwQCfZyZU tHPAxGJ5DdwTafK6NLCKTLo= =IWVy -----END PGP SIGNATURE----- --cy9Nn4fUvYST66Pl--
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