On Mon, 21 Sep 2015 11:24:29 +0200 Jan Kara <jack@xxxxxxx> wrote: > On Sat 19-09-15 08:17:14, Dave Chinner wrote: > > On Thu, Sep 17, 2015 at 11:04:03PM -0700, Linus Torvalds wrote: > > > On Thu, Sep 17, 2015 at 10:40 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > > > PS: just hit another "did this just get broken in 4.3-rc1" issue - I > > > > can't run blktrace while there's a IO load because: > > > > > > > > $ sudo blktrace -d /dev/vdc > > > > BLKTRACESETUP(2) /dev/vdc failed: 5/Input/output error > > > > Thread 1 failed open /sys/kernel/debug/block/(null)/trace1: 2/No such file or directory > > > > .... > > > > > > > > [ 641.424618] blktrace: page allocation failure: order:5, mode:0x2040d0 > > > > [ 641.438933] [<ffffffff811c1569>] kmem_cache_alloc_trace+0x129/0x400 > > > > [ 641.440240] [<ffffffff811424f8>] relay_open+0x68/0x2c0 > > > > [ 641.441299] [<ffffffff8115deb1>] do_blk_trace_setup+0x191/0x2d0 > > > > > > > > gdb) l *(relay_open+0x68) > > > > 0xffffffff811424f8 is in relay_open (kernel/relay.c:582). > > > > 577 return NULL; > > > > 578 if (subbuf_size > UINT_MAX / n_subbufs) > > > > 579 return NULL; > > > > 580 > > > > 581 chan = kzalloc(sizeof(struct rchan), GFP_KERNEL); > > > > 582 if (!chan) > > > > 583 return NULL; > > > > 584 > > > > 585 chan->version = RELAYFS_CHANNEL_VERSION; > > > > 586 chan->n_subbufs = n_subbufs; > > > > > > > > and struct rchan has a member struct rchan_buf *buf[NR_CPUS]; > > > > and CONFIG_NR_CPUS=8192, hence the attempt at an order 5 allocation > > > > that fails here.... > > > > > > Hm. Have you always had MAX_SMP (and the NR_CPU==8192 that it causes)? > > > From a quick check, none of this code seems to be new. > > > > Yes, I always build MAX_SMP kernels for testing, because XFS is > > often used on such machines and so I want to find issues exactly > > like this in my testing rather than on customer machines... :/ > > > > > That said, having that > > > > > > struct rchan_buf *buf[NR_CPUS]; > > > > > > in "struct rchan" really is something we should fix. We really should > > > strive to not allocate things by CONFIG_NR_CPU's, but by the actual > > > real CPU count. > > > > *nod*. But it doesn't fix the problem of the memory allocation > > failing when there's still gigabytes of immediately reclaimable > > memory available in the page cache. If this is failing under page > > cache memory pressure, then we're going to be doing an awful lot > > more falling back to vmalloc in the filesystem code where large > > allocations like this are done e.g. extended attribute buffers are > > order-5, and used a lot when doing things like backups which tend to > > also produce significant page cache memory pressure. > > > > Hence I'm tending towards there being a memory reclaim behaviour > > regression, not so much worrying about whether this specific > > allocation is optimal or not. > > Yup, looks like a regression in reclaim. Added linux-mm folks to CC. That's going to be hard to find. Possibly Vlastimil's 5-patch series "mm, compaction: more robust check for scanners meeting", possibly Joonsoo's "mm/compaction: correct to flush migrated pages if pageblock skip happens". But probably something else :( Teach relay.c about alloc_percpu()? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>