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

Baoquan He
2024-02-23T10:26:51Z

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