Re: [PATCH v3 00/11] Mitigate a vmap lock contention v3

[Baoquan He]

On 02/23/24 at 07:55pm, Uladzislau Rezki wrote:
> On Fri, Feb 23, 2024 at 11:57:25PM +0800, Baoquan He wrote:
> > On 02/23/24 at 12:06pm, Uladzislau Rezki wrote:
> > > > On 02/23/24 at 10:34am, Uladzislau Rezki wrote:
> > > > > On Thu, Feb 22, 2024 at 11:15:59PM +0000, Pedro Falcato wrote:
> > > > > > Hi,
> > > > > > 
> > > > > > On Thu, Feb 22, 2024 at 8:35 AM Uladzislau Rezki <urezki@xxxxxxxxx> wrote:
> > > > > > >
> > > > > > > Hello, Folk!
> > > > > > >
> > > > > > >[...]
> > > > > > > pagetable_alloc - gets increased as soon as a higher pressure is applied by
> > > > > > > increasing number of workers. Running same number of jobs on a next run
> > > > > > > does not increase it and stays on same level as on previous.
> > > > > > >
> > > > > > > /**
> > > > > > >  * pagetable_alloc - Allocate pagetables
> > > > > > >  * @gfp:    GFP flags
> > > > > > >  * @order:  desired pagetable order
> > > > > > >  *
> > > > > > >  * pagetable_alloc allocates memory for page tables as well as a page table
> > > > > > >  * descriptor to describe that memory.
> > > > > > >  *
> > > > > > >  * Return: The ptdesc describing the allocated page tables.
> > > > > > >  */
> > > > > > > static inline struct ptdesc *pagetable_alloc(gfp_t gfp, unsigned int order)
> > > > > > > {
> > > > > > >         struct page *page = alloc_pages(gfp | __GFP_COMP, order);
> > > > > > >
> > > > > > >         return page_ptdesc(page);
> > > > > > > }
> > > > > > >
> > > > > > > Could you please comment on it? Or do you have any thought? Is it expected?
> > > > > > > Is a page-table ever shrink?
> > > > > > 
> > > > > > It's my understanding that the vunmap_range helpers don't actively
> > > > > > free page tables, they just clear PTEs. munmap does free them in
> > > > > > mmap.c:free_pgtables, maybe something could be worked up for vmalloc
> > > > > > too.
> > > > > >
> > > > > Right. I see that for a user space, pgtables are removed. There was a
> > > > > work on it.
> > > > > 
> > > > > >
> > > > > > I would not be surprised if the memory increase you're seeing is more
> > > > > > or less correlated to the maximum vmalloc footprint throughout the
> > > > > > whole test.
> > > > > > 
> > > > > Yes, the vmalloc footprint follows the memory usage. Some uses cases
> > > > > map lot of memory.
> > > > 
> > > > The 'nr_threads=256' testing may be too radical. I took the test on
> > > > a bare metal machine as below, it's still running and hang there after
> > > > 30 minutes. I did this after system boot. I am looking for other
> > > > machines with more processors.
> > > > 
> > > > [root@dell-r640-068 ~]# nproc 
> > > > 64
> > > > [root@dell-r640-068 ~]# free -h
> > > >                total        used        free      shared  buff/cache   available
> > > > Mem:           187Gi        18Gi       169Gi        12Mi       262Mi       168Gi
> > > > Swap:          4.0Gi          0B       4.0Gi
> > > > [root@dell-r640-068 ~]# 
> > > > 
> > > > [root@dell-r640-068 linux]# tools/testing/selftests/mm/test_vmalloc.sh run_test_mask=127 nr_threads=256
> > > > Run the test with following parameters: run_test_mask=127 nr_threads=256
> > > > 
> > > Agree, nr_threads=256 is a way radical :) Mine took 50 minutes to
> > > complete. So wait more :)
> > 
> > Right, mine could take the similar time to finish that. I got a machine
> > with 288 cpus, see if I can get some clues. When I go through the code
> > flow, suddenly realized it could be drain_vmap_area_work which is the 
> > bottle neck and cause the tremendous page table pages costing.
> > 
> > On your system, there's 64 cpus. then 
> > 
> > nr_lazy_max = lazy_max_pages() = 7*32M = 224M;
> > 
> > So with nr_threads=128 or 256, it's so easily getting to the nr_lazy_max
> > and triggering drain_vmap_work(). When cpu resouce is very limited, the
> > lazy vmap purging will be very slow. While the alloc/free in lib/tet_vmalloc.c 
> > are going far faster and more easily then vmap reclaiming. If old va is not
> > reused, new va is allocated and keep extending, the new page table surely
> > need be created to cover them.
> > 
> > I will take testing on the system with 288 cpus, will update if testing
> > is done.
> > 
> <snip>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 12caa794abd4..a90c5393d85f 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1754,6 +1754,8 @@ size_to_va_pool(struct vmap_node *vn, unsigned long size)
>  	return NULL;
>  }
>  
> +static unsigned long lazy_max_pages(void);
> +
>  static bool
>  node_pool_add_va(struct vmap_node *n, struct vmap_area *va)
>  {
> @@ -1763,6 +1765,9 @@ node_pool_add_va(struct vmap_node *n, struct vmap_area *va)
>  	if (!vp)
>  		return false;
>  
> +	if (READ_ONCE(vp->len) > lazy_max_pages())
> +		return false;
> +
>  	spin_lock(&n->pool_lock);
>  	list_add(&va->list, &vp->head);
>  	WRITE_ONCE(vp->len, vp->len + 1);
> @@ -2170,9 +2175,9 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end,
>  				INIT_WORK(&vn->purge_work, purge_vmap_node);
>  
>  				if (cpumask_test_cpu(i, cpu_online_mask))
> -					schedule_work_on(i, &vn->purge_work);
> +					queue_work_on(i, system_highpri_wq, &vn->purge_work);
>  				else
> -					schedule_work(&vn->purge_work);
> +					queue_work(system_highpri_wq, &vn->purge_work);
>  
>  				nr_purge_helpers--;
>  			} else {
> <snip>
> 
> We need this. This settles it back to a normal PTE-usage. Tomorrow i
> will check if cache-len should be limited. I tested on my 64 CPUs
> system with radical 256 kworkers. It looks good.

I finally finished the testing w/o and with your above improvement
patch. Testing is done on a system with 128 cpus. The system with 288
cpus is not available because of some console connection. Attach the log
here. In some testing after rebooting, I found it could take more than 30
minutes, I am not sure if it's caused by my messy code change. I finally
cleaned up all of them and take a clean linux-next to test, then apply
your above draft code.
[root@dell-per6515-03 linux]# nproc 
128
[root@dell-per6515-03 linux]# free -h
               total        used        free      shared  buff/cache   available
Mem:           124Gi       2.6Gi       122Gi        21Mi       402Mi       122Gi
Swap:          4.0Gi          0B       4.0Gi

1)linux-next kernel w/o improving code from Uladzislau
-------------------------------------------------------
[root@dell-per6515-03 linux]# time tools/testing/selftests/mm/test_vmalloc.sh run_test_mask=127 nr_threads=64
Run the test with following parameters: run_test_mask=127 nr_threads=64
Done.
Check the kernel ring buffer to see the summary.

real	4m28.018s
user	0m0.015s
sys	0m4.712s
[root@dell-per6515-03 ~]# sort -h /proc/allocinfo | tail -10
    21405696     5226 mm/memory.c:1122 func:folio_prealloc 
    26199936     7980 kernel/fork.c:309 func:alloc_thread_stack_node 
    29822976     7281 mm/readahead.c:247 func:page_cache_ra_unbounded 
    99090432    96768 drivers/iommu/iova.c:604 func:iova_magazine_alloc 
   107638784     6320 mm/readahead.c:468 func:ra_alloc_folio 
   120560528    29439 mm/mm_init.c:2521 func:alloc_large_system_hash 
   134742016    32896 mm/percpu-vm.c:95 func:pcpu_alloc_pages 
   263192576    64256 mm/page_ext.c:270 func:alloc_page_ext 
   266797056    65136 include/linux/mm.h:2848 func:pagetable_alloc 
   507617280    32796 mm/slub.c:2305 func:alloc_slab_page 
[root@dell-per6515-03 ~]# 
[root@dell-per6515-03 ~]# 
[root@dell-per6515-03 linux]# time tools/testing/selftests/mm/test_vmalloc.sh run_test_mask=127 nr_threads=128
Run the test with following parameters: run_test_mask=127 nr_threads=128
Done.
Check the kernel ring buffer to see the summary.

real	6m19.328s
user	0m0.005s
sys	0m9.476s
[root@dell-per6515-03 ~]# sort -h /proc/allocinfo | tail -10
    21405696     5226 mm/memory.c:1122 func:folio_prealloc 
    26889408     8190 kernel/fork.c:309 func:alloc_thread_stack_node 
    29822976     7281 mm/readahead.c:247 func:page_cache_ra_unbounded 
    99090432    96768 drivers/iommu/iova.c:604 func:iova_magazine_alloc 
   107638784     6320 mm/readahead.c:468 func:ra_alloc_folio 
   120560528    29439 mm/mm_init.c:2521 func:alloc_large_system_hash 
   134742016    32896 mm/percpu-vm.c:95 func:pcpu_alloc_pages 
   263192576    64256 mm/page_ext.c:270 func:alloc_page_ext 
   550068224    34086 mm/slub.c:2305 func:alloc_slab_page 
   664535040   162240 include/linux/mm.h:2848 func:pagetable_alloc 
[root@dell-per6515-03 ~]# 
[root@dell-per6515-03 ~]# 
[root@dell-per6515-03 linux]# time tools/testing/selftests/mm/test_vmalloc.sh run_test_mask=127 nr_threads=256
Run the test with following parameters: run_test_mask=127 nr_threads=256
Done.
Check the kernel ring buffer to see the summary.

real	19m10.657s
user	0m0.015s
sys	0m20.959s
[root@dell-per6515-03 ~]# sort -h /proc/allocinfo | tail -10
    22441984     5479 mm/shmem.c:1634 func:shmem_alloc_folio 
    26758080     8150 kernel/fork.c:309 func:alloc_thread_stack_node 
    35880960     8760 mm/readahead.c:247 func:page_cache_ra_unbounded 
    99090432    96768 drivers/iommu/iova.c:604 func:iova_magazine_alloc 
   120560528    29439 mm/mm_init.c:2521 func:alloc_large_system_hash 
   122355712     7852 mm/readahead.c:468 func:ra_alloc_folio 
   134742016    32896 mm/percpu-vm.c:95 func:pcpu_alloc_pages 
   263192576    64256 mm/page_ext.c:270 func:alloc_page_ext 
   708231168    50309 mm/slub.c:2305 func:alloc_slab_page 
  1107296256   270336 include/linux/mm.h:2848 func:pagetable_alloc 
[root@dell-per6515-03 ~]# 

2)linux-next kernel with improving code from Uladzislau
-----------------------------------------------------
[root@dell-per6515-03 linux]# time tools/testing/selftests/mm/test_vmalloc.sh run_test_mask=127 nr_threads=64
Run the test with following parameters: run_test_mask=127 nr_threads=64
Done.
Check the kernel ring buffer to see the summary.

real	4m27.226s
user	0m0.006s
sys	0m4.709s
[root@dell-per6515-03 linux]# sort -h /proc/allocinfo | tail -10
    38023168     9283 mm/readahead.c:247 func:page_cache_ra_unbounded 
    72228864    17634 fs/xfs/xfs_buf.c:390 [xfs] func:xfs_buf_alloc_pages 
    99090432    96768 drivers/iommu/iova.c:604 func:iova_magazine_alloc 
    99863552    97523 fs/xfs/xfs_icache.c:81 [xfs] func:xfs_inode_alloc 
   120560528    29439 mm/mm_init.c:2521 func:alloc_large_system_hash 
   136314880    33280 mm/percpu-vm.c:95 func:pcpu_alloc_pages 
   184176640    10684 mm/readahead.c:468 func:ra_alloc_folio 
   263192576    64256 mm/page_ext.c:270 func:alloc_page_ext 
   284700672    69507 include/linux/mm.h:2848 func:pagetable_alloc 
   601427968    36377 mm/slub.c:2305 func:alloc_slab_page 
[root@dell-per6515-03 linux]# time tools/testing/selftests/mm/test_vmalloc.sh run_test_mask=127 nr_threads=128
Run the test with following parameters: run_test_mask=127 nr_threads=128
Done.
Check the kernel ring buffer to see the summary.

real	6m16.960s
user	0m0.007s
sys	0m9.465s
[root@dell-per6515-03 linux]# sort -h /proc/allocinfo | tail -10
    38158336     9316 mm/readahead.c:247 func:page_cache_ra_unbounded 
    72220672    17632 fs/xfs/xfs_buf.c:390 [xfs] func:xfs_buf_alloc_pages 
    99090432    96768 drivers/iommu/iova.c:604 func:iova_magazine_alloc 
    99863552    97523 fs/xfs/xfs_icache.c:81 [xfs] func:xfs_inode_alloc 
   120560528    29439 mm/mm_init.c:2521 func:alloc_large_system_hash 
   136314880    33280 mm/percpu-vm.c:95 func:pcpu_alloc_pages 
   184504320    10710 mm/readahead.c:468 func:ra_alloc_folio 
   263192576    64256 mm/page_ext.c:270 func:alloc_page_ext 
   427884544   104464 include/linux/mm.h:2848 func:pagetable_alloc 
   697311232    45159 mm/slub.c:2305 func:alloc_slab_page
[root@dell-per6515-03 linux]# time tools/testing/selftests/mm/test_vmalloc.sh run_test_mask=127 nr_threads=256
Run the test with following parameters: run_test_mask=127 nr_threads=256
Done.
Check the kernel ring buffer to see the summary.

real	21m15.673s
user	0m0.008s
sys	0m20.259s
[root@dell-per6515-03 linux]# sort -h /proc/allocinfo | tail -10
    38158336     9316 mm/readahead.c:247 func:page_cache_ra_unbounded 
    72224768    17633 fs/xfs/xfs_buf.c:390 [xfs] func:xfs_buf_alloc_pages 
    99090432    96768 drivers/iommu/iova.c:604 func:iova_magazine_alloc 
    99863552    97523 fs/xfs/xfs_icache.c:81 [xfs] func:xfs_inode_alloc 
   120560528    29439 mm/mm_init.c:2521 func:alloc_large_system_hash 
   136314880    33280 mm/percpu-vm.c:95 func:pcpu_alloc_pages 
   184504320    10710 mm/readahead.c:468 func:ra_alloc_folio 
   263192576    64256 mm/page_ext.c:270 func:alloc_page_ext 
   506974208   123773 include/linux/mm.h:2848 func:pagetable_alloc 
   809504768    53621 mm/slub.c:2305 func:alloc_slab_page
[root@dell-per6515-03 linux]# time tools/testing/selftests/mm/test_vmalloc.sh run_test_mask=127 nr_threads=256
Run the test with following parameters: run_test_mask=127 nr_threads=256
Done.
Check the kernel ring buffer to see the summary.

real	21m36.580s
user	0m0.012s
sys	0m19.912s
[root@dell-per6515-03 linux]# sort -h /proc/allocinfo | tail -10
    38977536     9516 mm/readahead.c:247 func:page_cache_ra_unbounded 
    72273920    17645 fs/xfs/xfs_buf.c:390 [xfs] func:xfs_buf_alloc_pages 
    99090432    96768 drivers/iommu/iova.c:604 func:iova_magazine_alloc 
    99895296    97554 fs/xfs/xfs_icache.c:81 [xfs] func:xfs_inode_alloc 
   120560528    29439 mm/mm_init.c:2521 func:alloc_large_system_hash 
   141033472    34432 mm/percpu-vm.c:95 func:pcpu_alloc_pages 
   186064896    10841 mm/readahead.c:468 func:ra_alloc_folio 
   263192576    64256 mm/page_ext.c:270 func:alloc_page_ext 
   541237248   132138 include/linux/mm.h:2848 func:pagetable_alloc 
   694718464    41216 mm/slub.c:2305 func:alloc_slab_page