Date: Sun, 12 Jul 2020 18:09:41 -0700 From: John-Mark Gurney <jmg@funkthat.com> To: d@delphij.net Cc: freebsd-current@freebsd.org Subject: Re: Is there any error checking on swap? Message-ID: <20200713010941.GK4213@funkthat.com> In-Reply-To: <a5b48324-c02c-b087-7da4-be66e447599f@delphij.net> References: <20200712033332.GA63411@www.zefox.net> <20200712072911.GG4213@funkthat.com> <a5b48324-c02c-b087-7da4-be66e447599f@delphij.net>
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--e9ndEBTQFD7P4kUb Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Xin Li wrote this message on Sun, Jul 12, 2020 at 15:06 -0700: >=20 >=20 > On 7/12/20 12:29 AM, John-Mark Gurney wrote: > > bob prohaska wrote this message on Sat, Jul 11, 2020 at 20:33 -0700: > >> Is there any error checking on swap traffic, along the lines of > >> a checksum or parity test?=20 > >> > >> Just curious what happens if a page written out is corrupted when > >> it comes back. > >=20 > > Looks like it doesn't: > > https://svnweb.freebsd.org/base/head/sys/vm/swap_pager.c?annotate=3D361= 965#l1389 >=20 > Technically one can enable checks with e.g. geli(8), but note that the > geli(8) provider will not "prime" the HMAC data so attaching the device > will immediately spam the system log with some authentication errors due > to GEOM tasting (because the kernel would try to read locations that > potentially contain metadata for other GEOM providers). Yeah, and enabling auth w/ geli(8) is problematic, as it creates a disconnect between layers, as it expands 4096 byte writes to 9 512 byte sector writes, if you're using a 4k drive (which is pretty much the only thing sold these days), the performance is likely to be pretty terrible... see: https://svnweb.freebsd.org/base/head/sys/geom/eli/g_eli_integrity.c?annotat= e=3D361481#l56 So, it'd be doable, but less than ideal... > For the case of swap, since the write is always page sized, it's > probably optimal to implement something in the swap layer itself and > store the expected checksums in memory. +1 --=20 John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not." --e9ndEBTQFD7P4kUb Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQJ8BAEBCgBmBQJfC7RUXxSAAAAAAC4AKGlzc3Vlci1mcHJAbm90YXRpb25zLm9w ZW5wZ3AuZmlmdGhob3JzZW1hbi5uZXQ2MEI1RTRGMTNDNzYyMDZDNjEyMDBCNjAy MDVGMEIzM0REMDA2QURBAAoJECBfCzPdAGrakmUQAKcZeuy8dCLIfJfwcCS/+mrd ThVb+JYaVUDv1vavVU4iXH66/Nqw7+WC29ZrMOJCtQ8ttSRahzn5xpOt3xSXt+Ks Hk8qfdpPOgK35QVmwJFncpqAzhY020JKHk79+xssBs0ukxF+KRk0RIrR26av2iTF 5Prz3eIQv16OedQWYJXxXLW3umNbt2OPzI3pl1Kd8FpEE2/xRuvH1NmVxuHadDtB FK2VNdiumSEHhXbya6O/nCNljzlmLZ3X7OEa9YHsCJ6+gM/s/LAq0kvizigfNX5Q o0UCTmvURvtmOYuzhJd0ZwwDWM4+X0DkdKGJhGmw7pOizFqKtH1mnbSBKRjPcz5q MRG1tHYZ+EffB3aGKPfsuEZNXQtsuJz5B9atkoju8v0ELLa6Xt0x+F6NFY19jg5F vYEOdhC7PdX4GT1z+7S5UrWfZBISd0zAssZcXKKJLXQtVtT2kriFr35jhWXndF/l VDs+W7Uy4Er9tqxCxKVfbJIwmvFTShBu2/Zk7qanIGTncnBw1+GIJOmN+nuAkRf5 mJZvlHZH3D9wrqpqMZhtO7n4C4BCZi3wrUW7g6DSLq8DJD9cddvM0xz8vNieJ2Sa qwed+ZLb3L9pT/v3gOYj2UYaKcxG9HskqTxYf6c2jJRsbLihNkG608aL6xnDHB/5 sXD0vlegZSLxeQZPR51o =nyzJ -----END PGP SIGNATURE----- --e9ndEBTQFD7P4kUb--
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