On Wed, 11.06.14 20:32, Chris Murphy (li...@colorremedies.com) wrote: > > systemd has a very stupid journal write pattern. It checks if there > > is space in the file for the write, and if not it fallocates the > > small amount of space it needs (it does *4 byte* fallocate calls!)
Not really the case. http://cgit.freedesktop.org/systemd/systemd/tree/src/journal/journal-file.c#n354 We allocate 8mb at minimum. > > and then does the write to it. All this does is fragment the crap > > out of the log files because the filesystems cannot optimise the > > allocation patterns. Well, it would be good if you'd tell me what to do instead... I am invoking fallocate() in advance, because we write those files with mmap() and that of course would normally triggered SIGBUS already on the most boring of reasons, such as disk full/quota full or so. Hence, before we do anything like that, we invoke fallocate() to ensure that the space is actually available... As far as I can see, that pretty much in line with what fallocate() is supposed to be useful for, the man page says this explicitly: "...After a successful call to posix_fallocate(), subsequent writes to bytes in the specified range are guaranteed not to fail because of lack of disk space." Happy to be informed that the man page is wrong. I am also happy to change our code, if it really is the wrong thing to do. Note however that I generally favour correctness and relying on documented behaviour, instead of nebulous optimizations whose effects might change with different file systems or kernel versions... > > Yup, it fragments journal files on XFS, too. > > > > http://oss.sgi.com/archives/xfs/2014-03/msg00322.html > > > > IIRC, the systemd developers consider this a filesystem problem and > > so refused to change the systemd code to be nice to the filesystem > > allocators, even though they don't actually need to use fallocate... What? No need to be dick. Nobody ever pinged me about this. And yeah, I think I have a very good reason to use fallocate(). The only reason in fact the man page explicitly mentions. Lennart -- Lennart Poettering, Red Hat _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
