Date:   Sat, 16 Oct 2021 18:46:24 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Nicholas Piggin <npiggin@...il.com>,
        Chen Wandun <chenwandun@...wei.com>
Cc:     Chen Wandun <chenwandun@...wei.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Eric Dumazet <edumazet@...gle.com>, guohanjun@...wei.com,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: Re: [PATCH] mm/vmalloc: fix numa spreading for large hash tables

On Fri, Oct 15, 2021 at 05:11:25PM +1000, Nicholas Piggin wrote:
> Excerpts from Chen Wandun's message of October 15, 2021 12:31 pm:
> > 
> > 
> > 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@...wei.com> 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@mail.gmail.com/
> >>>>>
> >>>>> [2]
> >>>>> https://lore.kernel.org/linux-mm/CANn89iLofTR=AK-QOZY87RdUZENCZUT4O6a0hvhu3_EwRMerOg@mail.gmail.com/
> >>>>>
> >>>>> Fixes: 121e6f3258fe ("mm/vmalloc: hugepage vmalloc mappings")
> >>>>> Reported-by: Eric Dumazet <edumazet@...gle.com>
> >>>>> Signed-off-by: Chen Wandun <chenwandun@...wei.com>
> >>>>> ---
> >>>>>    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
> 
> Okay. It would be better to do it as two patches. First the minimal fix 
> so it can be backported easily and have the Fixes: tag pointed at my 
> commit. Then the performance optimization.
> 
It is not only your commit. It also fixes my one :)

<snip>
commit 5c1f4e690eecc795b2e4d4408e87302040fceca4
Author: Uladzislau Rezki (Sony) <urezki@...il.com>
Date:   Mon Jun 28 19:40:14 2021 -0700

    mm/vmalloc: switch to bulk allocator in __vmalloc_area_node()
<snip>

I agree there should be two separate patches which fix NUMA balancing
issue, tagged with "Fixes" flag. One is located here:

https://lkml.org/lkml/2021/10/15/1172

second one should be that fixes a second place where "big" pages are
allocated, basically your patch.

--
Vlad Rezki

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