On Mon, Jul 18, 2016 at 09:14:00PM +1000, Dave Chinner wrote: > On Thu, Jun 30, 2016 at 07:22:39PM +0200, Christoph Hellwig wrote: > > On Tue, Jun 28, 2016 at 10:26:49AM +1000, Dave Chinner wrote: > > > Christoph, it look slike there's an ENOSPC+ENOMEM behavioural regression here. > > > generic/224 on my 1p/1GB RAM VM using a 1k lock size filesystem has > > > significantly different behaviour once ENOSPC is hit withi this patchset. > > > > > > It ends up with an endless stream of errors like this: > > > > I've spent some time trying to reproduce this. I'm actually getting > > the OOM killer almost reproducible for for-next without the iomap > > patches as well when just using 1GB of mem. 1400 MB is the minimum > > I can reproducibly finish the test with either code base. > > > > But with the 1400 MB setup I see a few interesting things. Even > > with the baseline, no-iomap case I see a few errors in the log: > > > > [ 70.407465] Filesystem "vdc": reserve blocks depleted! Consider increasing > > reserve pool > > size. > > [ 70.195645] XFS (vdc): page discard on page ffff88005682a988, inode 0xd3, offset 761856. > > [ 70.408079] Buffer I/O error on dev vdc, logical block 1048513, lost async > > page write > > [ 70.408598] Buffer I/O error on dev vdc, logical block 1048514, lost async > > page write > > 27s > > > > With iomap I also see the spew of page discard errors your see, but while > > I see a lot of them, the rest still finishes after a reasonable time, > > just a few seconds more than the pre-iomap baseline. I also see the > > reserve block depleted message in this case. > > > > Digging into the reserve block depleted message - it seems we have > > too many parallel iomap_allocate transactions going on. I suspect > > this might be because the writeback code will not finish a writeback > > context if we have multiple blocks inside a page, which can > > happen easily for this 1k ENOSPC setup. I've not had time to fully > > check if this is what really happens, but I did a quick hack (see below) > > to only allocate 1k at a time in iomap_begin, and with that generic/224 > > finishes without the warning spew. Of course this isn't a real fix, > > and I need to fully understand what's going on in writeback due to > > different allocation / dirtying patterns from the iomap change. > > Any progress here, Christoph? The current test run has been running > generic/224 on the 1GB mem test Vm for almost 6 hours now, and it's > still discarding pages. This doesn't always happen - sometimes it > takes the normal amount of time to run, but every so often it falls > into this "discard every page" loop and it takes hours to > complete... .... and I've now got a 16p/16GB RAM VM stuck in this loop in generic/224, so it's not limited to low memory machines.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
