On Tue, Aug 26, 2025 at 02:23:12PM +0200, cem@xxxxxxxxxx wrote: > From: Carlos Maiolino <cem@xxxxxxxxxx> > > Valid values for logbsize depends on whether log_sunit is set > on the filesystem or not and if logbsize is manually set or not. > > When manually set, logbsize must be one of the speficied values - > 32k to 256k inclusive in power-of-to increments. And, the specified > value must also be a multiple of log_sunit. > > The default configuration for v2 logs uses a relaxed restriction, > setting logbsize to log_sunit, independent if it is one of the valid > values or not - also implicitly ignoring the power of two restriction. > > Instead of changing valid possible values for logbsize, increasing the > testing matrix and allowing users to use some dubious configuration, > just update the man page to describe this difference in behavior when > manually setting logbsize or leave it to defaults. > > This has originally been found by an user attempting to manually set > logbsize to the same value picked by the default configuration just so > to receive an error message as result. > > Signed-off-by: Carlos Maiolino <cmaiolino@xxxxxxxxxx> > --- > man/man5/xfs.5 | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/man/man5/xfs.5 b/man/man5/xfs.5 > index f9c046d4721a..b2069d17b0fe 100644 > --- a/man/man5/xfs.5 > +++ b/man/man5/xfs.5 > @@ -246,16 +246,18 @@ controls the size of each buffer and so is also relevant to > this case. > .TP > .B logbsize=value > -Set the size of each in-memory log buffer. The size may be > +Set the size of each in-memory log buffer. The size may be > specified in bytes, or in kibibytes (KiB) with a "k" suffix. > +If set manually, logbsize must be one of the specified valid > +sizes and a multiple of the log stripe unit - configured at mkfs time. > +.sp > Valid sizes for version 1 and version 2 logs are 16384 (value=16k) > and 32768 (value=32k). Valid sizes for version 2 logs also > -include 65536 (value=64k), 131072 (value=128k) and 262144 (value=256k). The > -logbsize must be an integer multiple of the log > -stripe unit configured at mkfs time. > +include 65536 (value=64k), 131072 (value=128k) and 262144 (value=256k). > .sp > The default value for version 1 logs is 32768, while the > -default value for version 2 logs is max(32768, log_sunit). > +default value for version 2 logs is max(32768, log_sunit) even if > +log_sunit does not match one of the valid values above. Weird, but as a documentation stopgap until someone figures out if there are any bad effects of non-power-of-2 logbsizes, Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx> --D > .TP > .BR logdev=device " and " rtdev=device > Use an external log (metadata journal) and/or real-time device. > -- > 2.51.0 > >
