On Tue, Sep 19, 2017 at 07:53:52PM +0200, Tomasz Grabiec wrote: > On Tue, Sep 19, 2017 at 7:38 PM, Brian Foster <bfoster@xxxxxxxxxx> wrote: > >> Is that because the disk is nearly full and there are no known flushed > >> extents, or because the allocator doesn't prioritize known-flushed extents? > >> From your comments below I gather you may not know for sure. > >> > > > > I'm not sure without digging further into it. Hence the question around > > free space availability. > > The file system was utilized between 90% and 95% out of 165GB during the test. Then I'm surprised that you only hit these relatively minor delays. Once you get beyond 85-90% full the filesystem is typically not running through allocation fast paths as large contiguous free spaces are getting to be non-existant (especially for such small filesystems like this). Continued operation at >85-90% full will run you into premature aging situations like free space fragmentation, and then all your allocations and then data IO patterns will begin to suffer. Once you get above 95% full, various algorithms will even stop attempting optimal allocations and instead start optimising for minimum size at the expense of increased file fragmentation. IOWs, expect unpredictable delays in the filesystem once you start approaching ENOSPC, and the closer to ENOSPC you get the more unpredictable the filesystem behaviour will get. And if you spend long periods of time operating near ENOSPC, performance and behaviour may not improve unless you free a large amount of space (e.g. 50% of filesystem space) so that large contiguous free space regions can reform.... So, yes, you can operate at near ENOSPC conditions. However, it's not advisable if you require deterministic/predictable behaviour and/or have long term filesystem performance requirements... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
