From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Mason Subject: Re: worse than expected compression ratios with -o compress Date: Thu, 21 Jan 2010 15:07:50 -0500 Message-ID: <20100121200750.GC23006@think> References: <20100118141240.GA10710@localhost.localdomain> <20100118212951.GC4065@think> <20100120163011.GE3001@think> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Cc: Jim Faulkner , Josef Bacik , linux-btrfs@vger.kernel.org To: Gregory Maxwell Return-path: In-Reply-To: List-ID: On Thu, Jan 21, 2010 at 03:04:56PM -0500, Gregory Maxwell wrote: > On Thu, Jan 21, 2010 at 1:16 PM, Jim Faulkner = wrote: > > > > On Wed, 20 Jan 2010, Chris Mason wrote: > > > >> Please let me know if this improves your ratios > > > > It most certainly does! =C2=A0It also greatly reduced the time requ= ired to copy > > the data to my (not very fast) disk. =C2=A0All my testing was done = on 2.6.32.4. > > The line numbers in your patch were a little off for 2.6.32.4, but = I did > > manage to apply it cleanly. =C2=A0Here's the results of my testing: > [snip] > > I'd be very happy to see the -o compress-force option in the mainli= ne kernel > > someday! >=20 >=20 > Sweet. But I think a force mount option is an unreasonably blunt tool= =2E >=20 > I think two things would be nice: >=20 > (1) Fix the compression decision, I think this example suggests that > something is broken. (I'd noticed poorer than expected compression on > my laptop, but I'd chalked it up to the 64k blocks=E2=80=A6 now I'm n= ot so > confident) The current code assumes that files have consistent data in them. This is very true for the average data set, but it'll be horribly wrong for something like a database file. >=20 > (2) An IOCTL for compression control. Userspace knows best, some > files ought to have a different compression policy. Yes, we'll get #2 added. -chris -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" = in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html