Re: [PATCH] mm/vmalloc: fix numa spreading for large hash tables

[Chen Wandun]

在 2021/10/15 9:34, Nicholas Piggin 写道:
> Excerpts from Chen Wandun's message of October 14, 2021 6:59 pm:
> > 在 2021/10/14 5:46, Shakeel Butt 写道:
> > > On Tue, Sep 28, 2021 at 5:03 AM Chen Wandun <chenwandun@xxxxxxxxxx> wrote:
> > > > Eric Dumazet reported a strange numa spreading info in [1], and found
> > > > commit 121e6f3258fe ("mm/vmalloc: hugepage vmalloc mappings") introduced
> > > > this issue [2].
> > > >
> > > > Dig into the difference before and after this patch, page allocation has
> > > > some difference:
> > > >
> > > > before:
> > > > alloc_large_system_hash
> > > >       __vmalloc
> > > >           __vmalloc_node(..., NUMA_NO_NODE, ...)
> > > >               __vmalloc_node_range
> > > >                   __vmalloc_area_node
> > > >                       alloc_page /* because NUMA_NO_NODE, so choose alloc_page branch */
> > > >                           alloc_pages_current
> > > >                               alloc_page_interleave /* can be proved by print policy mode */
> > > >
> > > > after:
> > > > alloc_large_system_hash
> > > >       __vmalloc
> > > >           __vmalloc_node(..., NUMA_NO_NODE, ...)
> > > >               __vmalloc_node_range
> > > >                   __vmalloc_area_node
> > > >                       alloc_pages_node /* choose nid by nuam_mem_id() */
> > > >                           __alloc_pages_node(nid, ....)
> > > >
> > > > So after commit 121e6f3258fe ("mm/vmalloc: hugepage vmalloc mappings"),
> > > > it will allocate memory in current node instead of interleaving allocate
> > > > memory.
> > > >
> > > > [1]
> > > > https://lore.kernel.org/linux-mm/CANn89iL6AAyWhfxdHO+jaT075iOa3XcYn9k6JJc7JR2XYn6k_Q@xxxxxxxxxxxxxx/
> > > >
> > > > [2]
> > > > https://lore.kernel.org/linux-mm/CANn89iLofTR=AK-QOZY87RdUZENCZUT4O6a0hvhu3_EwRMerOg@xxxxxxxxxxxxxx/
> > > >
> > > > Fixes: 121e6f3258fe ("mm/vmalloc: hugepage vmalloc mappings")
> > > > Reported-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> > > > Signed-off-by: Chen Wandun <chenwandun@xxxxxxxxxx>
> > > > ---
> > > >    mm/vmalloc.c | 33 ++++++++++++++++++++++++++-------
> > > >    1 file changed, 26 insertions(+), 7 deletions(-)
> > > >
> > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > > index f884706c5280..48e717626e94 100644
> > > > --- a/mm/vmalloc.c
> > > > +++ b/mm/vmalloc.c
> > > > @@ -2823,6 +2823,8 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
> > > >                   unsigned int order, unsigned int nr_pages, struct page **pages)
> > > >    {
> > > >           unsigned int nr_allocated = 0;
> > > > +       struct page *page;
> > > > +       int i;
> > > >
> > > >           /*
> > > >            * For order-0 pages we make use of bulk allocator, if
> > > > @@ -2833,6 +2835,7 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
> > > >           if (!order) {
> > >
> > > Can you please replace the above with if (!order && nid != NUMA_NO_NODE)?
> > >
> > > >                   while (nr_allocated < nr_pages) {
> > > >                           unsigned int nr, nr_pages_request;
> > > > +                       page = NULL;
> > > >
> > > >                           /*
> > > >                            * A maximum allowed request is hard-coded and is 100
> > > > @@ -2842,9 +2845,23 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
> > > >                            */
> > > >                           nr_pages_request = min(100U, nr_pages - nr_allocated);
> > >
> > > Undo the following change in this if block.
> >
> > Yes, It seem like more simpler as you suggested, But it still have
> > performance regression, I plan to change the following to consider
> > both mempolcy and alloc_pages_bulk.
>
> Thanks for finding and debugging this. These APIs are a maze of twisty
> little passages, all alike so I could be as confused as I was when I
> wrote that patch, but doesn't a minimal fix look something like this?

Yes, I sent a patch，it looks like as you show, besides it also
contains some performance optimization.

[PATCH] mm/vmalloc: introduce alloc_pages_bulk_array_mempolicy to 
accelerate memory allocation

Thanks,
Wandun

> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index d77830ff604c..75ee9679f521 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2860,7 +2860,10 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>                  struct page *page;
>                  int i;
>   
> -               page = alloc_pages_node(nid, gfp, order);
> +               if (nid == NUMA_NO_NODE)
> +                       page = alloc_pages(gfp, order);
> +               else
> +                       page = alloc_pages_node(nid, gfp, order);
>                  if (unlikely(!page))
>                          break;
>   
>
> Thanks,
> Nick
> .