Re: [PATCH v3 00/35] Memory allocation profiling

[Tim Chen]

On Mon, 2024-02-12 at 13:38 -0800, Suren Baghdasaryan wrote:
> Memory allocation, v3 and final:
> 
> Overview:
> Low overhead [1] per-callsite memory allocation profiling. Not just for debug
> kernels, overhead low enough to be deployed in production.
> 
> We're aiming to get this in the next merge window, for 6.9. The feedback
> we've gotten has been that even out of tree this patchset has already
> been useful, and there's a significant amount of other work gated on the
> code tagging functionality included in this patchset [2].
> 
> Example output:
>   root@moria-kvm:~# sort -h /proc/allocinfo|tail
>    3.11MiB     2850 fs/ext4/super.c:1408 module:ext4 func:ext4_alloc_inode
>    3.52MiB      225 kernel/fork.c:356 module:fork func:alloc_thread_stack_node
>    3.75MiB      960 mm/page_ext.c:270 module:page_ext func:alloc_page_ext
>    4.00MiB        2 mm/khugepaged.c:893 module:khugepaged func:hpage_collapse_alloc_folio
>    10.5MiB      168 block/blk-mq.c:3421 module:blk_mq func:blk_mq_alloc_rqs
>    14.0MiB     3594 include/linux/gfp.h:295 module:filemap func:folio_alloc_noprof
>    26.8MiB     6856 include/linux/gfp.h:295 module:memory func:folio_alloc_noprof
>    64.5MiB    98315 fs/xfs/xfs_rmap_item.c:147 module:xfs func:xfs_rui_init
>    98.7MiB    25264 include/linux/gfp.h:295 module:readahead func:folio_alloc_noprof
>     125MiB     7357 mm/slub.c:2201 module:slub func:alloc_slab_page
> 
> Since v2:
>  - tglx noticed a circular header dependency between sched.h and percpu.h;
>    a bunch of header cleanups were merged into 6.8 to ameliorate this [3].
> 
>  - a number of improvements, moving alloc_hooks() annotations to the
>    correct place for better tracking (mempool), and bugfixes.
> 
>  - looked at alternate hooking methods.
>    There were suggestions on alternate methods (compiler attribute,
>    trampolines), but they wouldn't have made the patchset any cleaner
>    (we still need to have different function versions for accounting vs. no
>    accounting to control at which point in a call chain the accounting
>    happens), and they would have added a dependency on toolchain
>    support.
> 
> Usage:
> kconfig options:
>  - CONFIG_MEM_ALLOC_PROFILING
>  - CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT
>  - CONFIG_MEM_ALLOC_PROFILING_DEBUG
>    adds warnings for allocations that weren't accounted because of a
>    missing annotation
> 
> sysctl:
>   /proc/sys/vm/mem_profiling
> 
> Runtime info:
>   /proc/allocinfo
> 
> Notes:
> 
> [1]: Overhead
> To measure the overhead we are comparing the following configurations:
> (1) Baseline with CONFIG_MEMCG_KMEM=n
> (2) Disabled by default (CONFIG_MEM_ALLOC_PROFILING=y &&
>     CONFIG_MEM_ALLOC_PROFILING_BY_DEFAULT=n)
> (3) Enabled by default (CONFIG_MEM_ALLOC_PROFILING=y &&
>     CONFIG_MEM_ALLOC_PROFILING_BY_DEFAULT=y)
> (4) Enabled at runtime (CONFIG_MEM_ALLOC_PROFILING=y &&
>     CONFIG_MEM_ALLOC_PROFILING_BY_DEFAULT=n && /proc/sys/vm/mem_profiling=1)
> (5) Baseline with CONFIG_MEMCG_KMEM=y && allocating with __GFP_ACCOUNT
> 

Thanks for the work on this patchset and it is quite useful.
A clarification question on the data:

I assume Config (2), (3) and (4) has CONFIG_MEMCG_KMEM=n, right?
If so do you have similar data for config (2), (3) and (4) but with
CONFIG_MEMCG_KMEM=y for comparison with (5)?

Tim

> Performance overhead:
> To evaluate performance we implemented an in-kernel test executing
> multiple get_free_page/free_page and kmalloc/kfree calls with allocation
> sizes growing from 8 to 240 bytes with CPU frequency set to max and CPU
> affinity set to a specific CPU to minimize the noise. Below are results
> from running the test on Ubuntu 22.04.2 LTS with 6.8.0-rc1 kernel on
> 56 core Intel Xeon:
> 
>                         kmalloc                 pgalloc
> (1 baseline)            6.764s                  16.902s
> (2 default disabled)    6.793s (+0.43%)         17.007s (+0.62%)
> (3 default enabled)     7.197s (+6.40%)         23.666s (+40.02%)
> (4 runtime enabled)     7.405s (+9.48%)         23.901s (+41.41%)
> (5 memcg)               13.388s (+97.94%)       48.460s (+186.71%)
>