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... 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
