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

Baoquan He
2024-02-28T09:27:18Z

[-- Attachment #1: Type: text/plain, Size: 5978 bytes --]

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@gmail.com> 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.

[-- Attachment #2: vmalloc_node.log --]
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[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