Re: [PATCH v2 2/4] mm: vmalloc: use rwsem, mutex for vmap_area_lock and vmap_block->lock

Uladzislau Rezki
2023-03-27T17:22:56Z

> So, this patch open codes the kvmalloc() in the commit path to have
> the above described behaviour. The result is we more than halve the
> CPU time spend doing kvmalloc() in this path and transaction commits
> with 64kB objects in them more than doubles. i.e. we get ~5x
> reduction in CPU usage per costly-sized kvmalloc() invocation and
> the profile looks like this:
>
> - 37.60% xlog_cil_commit
> 16.01% memcpy_erms
> - 8.45% __kmalloc
> - 8.04% kmalloc_order_trace
> - 8.03% kmalloc_order
> - 7.93% alloc_pages
> - 7.90% __alloc_pages
> - 4.05% __alloc_pages_slowpath.constprop.0
> - 2.18% get_page_from_freelist
> - 1.77% wake_all_kswapds
> ....
> - __wake_up_common_lock
> - 0.94% _raw_spin_lock_irqsave
> - 3.72% get_page_from_freelist
> - 2.43% _raw_spin_lock_irqsave
> - 5.72% vmalloc
> - 5.72% __vmalloc_node_range
> - 4.81% __get_vm_area_node.constprop.0
> - 3.26% alloc_vmap_area
> - 2.52% _raw_spin_lock
> - 1.46% _raw_spin_lock
> 0.56% __alloc_pages_bulk
> - 4.66% kvfree
> - 3.25% vfree
OK, i see. I tried to use the fs_mark in different configurations. For
example:

<snip>
time fs_mark -D 10000 -S0 -n 100000 -s 0 -L 32 -d ./scratch/0 -d ./scratch/1 -d ./scratch/2 \
-d ./scratch/3 -d ./scratch/4 -d ./scratch/5 -d ./scratch/6 -d ./scratch/7 -d ./scratch/8 \
-d ./scratch/9 -d ./scratch/10 -d ./scratch/11 -d ./scratch/12 -d ./scratch/13 \
-d ./scratch/14 -d ./scratch/15 -t 64 -F
<snip>

But i did not manage to trigger xlog_cil_commit() to fallback to vmalloc
code. I think i should reduce an amount of memory on my kvm-pc and
repeat the tests!

--
Uladzislau Rezki