lkml.org 
[lkml]   [2001]   [Nov]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: writing a plugin for reiserfs compression
Roy Sigurd Karlsbakk wrote:
>
> > > I just thought there was a patch doing windows nt-like
> > > compress-em-all-realtime-and-get-doomed!
> >
> > I don't know what the actual heuristics for determining which files are
> > compression with the ext2 patch. It is definitely NOT a compressed
> > block device. Files are compressed in chunks (32kB?), so that it is
> > possible to seek and do read-modify-write (e.g. appending to a file)
> > without decompressing the entire file and/or recompressing it. This also
> > protects against block corruption, since you would limit the amount of
> > data lost to the end of the chunk after the bad spot.
>
> But still... Are the files are compressed as they are created/modified on
> the filesystem? My main point was to avoid the compression overhead and
> just decompress the file at access time if it's compressed. Compression
> should (IMO) be done nightly.
>
> Perhaps a file should be decompressed when it's modified and either (a)
> set scheduled to next nightly compression or (b) stay uncompressed the
> next <n> days. I mean - as a file is being modified, the chance is large
> that the file will be accessed pretty soon...
>
> > Yes, definitely disabling compression for a file is good. The "accessed
> > in last 7 days flag" is questionable. This could be determined via the
> > atime on Unix and doesn't need a separate flag. Also, the difference
> > between "do not compress" and "can't compress" is very small. If it is
> > found that the file is incompressible, you could just as easily set the
> > "do not compress" flag.
>
> I agree on the 'accessed in last <n> days'. It'd be better to check atime.
>
> I'd still like to separate 'do not compress' and 'can't compress', as to
> show why the falg has been set - the former is set by the admin and the
> latter by the system.
>
> roy

I think you'll find it easiest to code it such that doing anything to the file
body, reading or writing, decompresses it. Fancier stuff can wait for later
versions.

Hans
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:12    [W:0.061 / U:4.520 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site