On Mon, Aug 15, 2016 at 04:48:36PM -0700, Linus Torvalds wrote: > On Mon, Aug 15, 2016 at 4:20 PM, Linus Torvalds > <torva...@linux-foundation.org> wrote: > > > > None of this code is all that new, which is annoying. This must have > > gone on forever, > > ... ooh. > > Wait, I take that back. > > We actually have some very recent changes that I didn't even think > about that went into this very merge window. .... > Mel? The issue is that Dave Chinner is seeing some nasty spinlock > contention on "mapping->tree_lock": > > > 31.18% [kernel] [k] __pv_queued_spin_lock_slowpath > > and one of the main paths is this: > > > - 30.29% kswapd > > - 30.23% shrink_node > > - 30.07% shrink_node_memcg.isra.75 > > - 30.15% shrink_inactive_list > > - 29.49% shrink_page_list > > - 22.79% __remove_mapping > > - 22.27% _raw_spin_lock_irqsave > > __pv_queued_spin_lock_slowpath > > so there's something ridiculously bad going on with a fairly simple benchmark. > > Dave's benchmark is literally just a "write a new 48GB file in > single-page chunks on a 4-node machine". Nothing odd - not rewriting > files, not seeking around, no nothing. > > You can probably recreate it with a silly > > dd bs=4096 count=$((12*1024*1024)) if=/dev/zero of=bigfile > > although Dave actually had something rather fancier, I think.
16p, 16GB RAM, fake_numa=4. Overwrite a 47GB file on a 48GB filesystem: # mkfs.xfs -f -d size=48g /dev/vdc # mount /dev/vdc /mnt/scratch # xfs_io -f -c "pwrite 0 47g" /mnt/scratch/fooey Wait for memory to fill and reclaim to kick in, then look at the profile. If you run it a second time, reclaim kicks in straight away. It's not the new code in 4.8 - it reproduces on 4.7 just fine, and probably will reproduce all the way back to when the memcg-aware writeback code was added.... -Dave. -- Dave Chinner da...@fromorbit.com
