On Thu, Jan 8, 2015 at 6:30 AM, Lennart Poettering <lenn...@poettering.net> wrote: > On Wed, 07.01.15 15:10, Josef Bacik (jba...@fb.com) wrote: > >> On 01/07/2015 12:43 PM, Lennart Poettering wrote: >> >Heya! >> > >> >Currently, systemd-journald's disk access patterns (appending to the >> >end of files, then updating a few pointers in the front) result in >> >awfully fragmented journal files on btrfs, which has a pretty >> >negative effect on performance when accessing them. >> >> I've been wondering if mount -o autodefrag would deal with this problem but >> I haven't had the chance to look into it. > > Hmm, I am kinda interested in a solution that I can just implement in > systemd/journald now and that will then just make things work for > people suffering by the problem. I mean, I can hardly make systemd > patch the mount options of btrfs just because I place a journal file > on some fs... > > Is "autodefrag" supposed to become a default one day? > > Anyway, given the pros and cons I have now changed journald to set the > nocow bit on newly created journal files. When files are rotated (and > we hence know we will never ever write again to them) the bit is tried > to be unset again, and a defrag ioctl will be invoked right > after. btrfs currently silently ignores that we unset the bit, and > leaves it set, but I figure i should try to unset it anyway, in case > it learns that one day. After all, after rotating the files there's no > reason to treat the files special anymore...
I don't think it makes sense to unset nocow on a non-zero byte file anymore than it makes sense to set it. The functional equivalent that'd need to be done is: touch system@<blah>.journal~ chattr -C system@<blah>.journal~ cp system@<blah>.journal system@<blah>.journal~ The copy won't have nocow set. I suggest just leaving it alone. +C the /var/log/journal/ directory before machine-name directories are created, and then everything in there automatically inherits +C upon creation. No need to unset or defrag, in particular on SSD's I think it's sorta pointless excess writing. Set it and forget it policy. -- Chris Murphy -- 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
