On Fri, Jul 10, 2015 at 11:09:04AM +0800, juncheng bai wrote: > Hi,All. > > Recently, I test xfs to verify kmem_alloc hang in > xfs_dir2_block_to_sf in kernel-3.14, for patch > b3f03bac8132207a20286d5602eda64500c19724. You do not need to spam the list if you do not get an immediate response to your initial question. As it is, you commented on the bug report a couple of days again where I explained exactly what the state of this problem was (i.e. you asked "why can't we just use vmalloc?") > After running for five hours , the output of warning all the time: > 2015-07-07T23:32:18.230120+00:00 server-69 kernel: XFS: possible > memory allocation deadlock in kmem_alloc (mode:0x8250 size:32832) And that's pretty clear what the trigger here is - the allocation is just over the PAGE_ALLOC_COSTLY_ORDER threshold. We see this retry come up at this point because that threshold changes the behaviour of memory reclaim and makes allocations more likely to fail... > The patch b3f03bac8132207a20286d5602eda64500c19724 solves the > problem of the big directroy size, more than 64k. > Now, the 'struct txfs_log_vec' need 32k, but fail when the physical > memory fragmentation is very serious; In the later, kmalloc may fail > when process 16k. Right now we have to choose between: - running small machines out of vmalloc space - triggering the OOM killer and killing random processes - failing the allocation whcih corrupts the filesystem in memory, so we need to shut down the filesystem - retrying until we succeed. We currently default to the least worst situation which is "retry until we succeed" because all the other situations are much worse (i.e. take the filesystem and/or machine down, rather than recover when memory becomes available again). As I said earlier, there is no quick fix for this problem and shouting at us about it isn't going to get it solved any sooner. > So, I think can we provide a unified solution? And I think why can't we > use vmalloc when kmalloc fails? I told you - there is limited vmalloc space on 32 bit systems, so vmalloc can also fail due to vmalloc space being unavaiable, even when there is plenty of memory available. i.e. on 32 bit systems vmalloc is a lot more unreliable than kmalloc(). IOws, while vmalloc might fix your specific problem on your machine, it is not a general solution to the problem of kmalloc failing large allocations when you run your system to OOM conditions. And, FWIW, you can reduce the impact of the problem simply by making your directory block size smaller..... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
