On Wednesday April 25, [EMAIL PROTECTED] wrote: > > [ 756.311074] BUG: at block/cfq-iosched.c:543 cfq_reposition_rq_rb() > [ 756.329615] [<c0204fa1>] cfq_merged_request+0x71/0x80 > [ 756.345046] [<c0204f30>] cfq_merged_request+0x0/0x80 > [ 756.360216] [<c01fb4ae>] elv_merged_request+0x4e/0x50 > [ 756.375647] [<c01ff1a7>] __make_request+0x1a7/0x2f0 > [ 756.390557] [<c01ff497>] generic_make_request+0x127/0x190 > [ 756.407025] [<c02bb011>] chunk_aligned_read+0x111/0x1c0 ^^^^^^^^^^^^^^^^^ > [ 756.422974] [<c01ff497>] generic_make_request+0x127/0x190 > [ 756.439443] [<c02bb448>] make_request+0x388/0x3b0 > [ 756.453834] [<c016e027>] __bio_add_page+0x147/0x1c0 > [ 756.468742] [<c016dbff>] bio_alloc_bioset+0x7f/0x150 > [ 756.483913] [<c02bac50>] raid5_mergeable_bvec+0x0/0x90 > [ 756.499604] [<c016e107>] bio_add_page+0x37/0x50 > [ 756.513473] [<c01ff497>] generic_make_request+0x127/0x190 > [ 756.529943] [<c013586a>] mempool_free+0x2a/0x60 > [ 756.543812] [<c016dadd>] bio_free+0x1d/0x40 > [ 756.556645] [<c01ff546>] submit_bio+0x46/0xc0 > [ 756.571389] [<c020a396>] radix_tree_node_alloc+0x16/0x60 > [ 756.587610] [<c020a5c2>] radix_tree_insert+0xe2/0x130 > [ 756.603039] [<c0139575>] __pagevec_lru_add+0x75/0x80 > [ 756.618207] [<c0171971>] mpage_bio_submit+0x11/0x20 > [ 756.633117] [<c01720e0>] mpage_readpages+0x100/0x140 ^^^^^^^^^^^^^^^
So it is a regular data read (not metadata of any sort) which is by-passing the stripe cache. I was expecting some sort of metadata read. I wander what this is merging in-front of... maybe a stripe-cache read. I guess it doesn't tell us anything really interesting, which is probably a good thing - it means everything else is working properly. I wonder if we should avoid bypassing the stripe cache if the needed stripes are already in the cache... or if at least one needed stripe is.... or if the array is degraded... Probably in the degraded case we should never bypass the cache, as if we do, then a sequential read of a full stripe will read every block twice. I'd better to some performance measurements. Thanks for all the patient testing. NeilBrown - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/