On Tue, 28 Sep 2021 20:10:40 +0800 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>
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 ;)
