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

Suren Baghdasaryan
2024-02-14T19:09:43Z

On Wed, Feb 14, 2024 at 10:54 AM Tim Chen <tim.c.chen@linux.intel.com> wrote:
>
> 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?

Yes, correct.

> If so do you have similar data for config (2), (3) and (4) but with
> CONFIG_MEMCG_KMEM=y for comparison with (5)?

I have data for these additional configs (didn't think there were that
important):
(6) Disabled by default (CONFIG_MEM_ALLOC_PROFILING=y &&
CONFIG_MEM_ALLOC_PROFILING_BY_DEFAULT=n) && CONFIG_MEMCG_KMEM=y
(7) Enabled by default (CONFIG_MEM_ALLOC_PROFILING=y &&
CONFIG_MEM_ALLOC_PROFILING_BY_DEFAULT=y) && CONFIG_MEMCG_KMEM=y

>
> 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%)

(6 default disabled+memcg) 13.332s (+97.10%) 48.105s (+184.61%)
(7 default enabled+memcg) 13.446s (+98.78%) 54.963s (+225.18%)

(6) shows a bit better performance than (5) but it's probably noise. I
would expect them to be roughly the same. Hope this helps.

> >
>
>