On Tue, Sep 20, 2016 at 07:59:44AM +0000, Duncan wrote: > Christoph Anton Mitterer posted on Mon, 19 Sep 2016 21:45:46 +0200 as > excerpted: > > > On Mon, 2016-09-19 at 17:27 +0200, David Sterba wrote: > > > >> > For specific features: > >> > - Autodefrag > >> > - didn't that also cause reflinks to be broken up? > >> > >> No and never had. > > > > Absolutely sure? One year ago, I was told that at first too so I started > > using it, but later on some (IIRC) developer said auto-defrag would also > > suffer from it. > > AFAIK it was Hugo that said he looked into that, and that (if I'm > representing it correctly) autodefrag breaks reflinks and triggers space- > using duplication much as defrag does, but that it does it on a much > smaller scale, since it (1) only triggers when some parts of a file are > being rewritten anyway, thus breaking the reflink for those specific > parts of the file due to COW (COW1 on otherwise NOCOW files) in any case, > and (2) unlike defrag, doesn't rewrite and thus break the reflinks on > entire files, just somewhat larger extents than the pure rewrite by > itself without autodefrag would. > > Thus making the reflink-breaking and duplication effect of autodefrag > there, but relatively quite small compared to on-demand per-file defrag.
I didn't investigate it -- It was my firmly-stated misunderstanding which caused someone (Filipe, I think) with much more actual knowledge to correct me, thus making the actual behaviour much clearer. :) I think your description is accurate as far as my current understanding goes. Hugo. > -- > Duncan - List replies preferred. No HTML msgs. > "Every nonfree program has a lord, a master -- > and if you use the program, he is your master." Richard Stallman > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Hugo Mills | There isn't a noun that can't be verbed. hugo@... carfax.org.uk | http://carfax.org.uk/ | PGP: E2AB1DE4 |
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