Messages in this thread | | | Date | Tue, 28 Sep 2021 15:33:02 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] mm/vmalloc: fix numa spreading for large hash tables |
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On Tue, 28 Sep 2021 20:10:40 +0800 Chen Wandun <chenwandun@huawei.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@google.com> > Signed-off-by: Chen Wandun <chenwandun@huawei.com>
This seems like it could cause significant performance regressions in some situations?
If "yes" then wouldn't a cc:stable be appropriate? And some (perhaps handwavy) quantification of the slowdown would help people understand why we're recommending a backport.
If "no" then why the heck do we have that feature in there anyway ;)
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