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From: Andrew Morton <akpm@linux-foundation.org>
To: Chen Wandun <chenwandun@huawei.com>
Cc: <npiggin@gmail.com>, <linux-mm@kvack.org>,
	<linux-kernel@vger.kernel.org>, <edumazet@google.com>,
	<wangkefeng.wang@huawei.com>, <guohanjun@huawei.com>
Subject: Re: [PATCH] mm/vmalloc: fix numa spreading for large hash tables
Date: Tue, 28 Sep 2021 15:33:02 -0700	[thread overview]
Message-ID: <20210928153302.f87537b5faac8637c3c5eb53@linux-foundation.org> (raw)
In-Reply-To: <20210928121040.2547407-1-chenwandun@huawei.com>

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 ;)


  reply	other threads:[~2021-09-28 22:33 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-28 12:10 [PATCH] mm/vmalloc: fix numa spreading for large hash tables Chen Wandun
2021-09-28 22:33 ` Andrew Morton [this message]
2021-10-14  8:50   ` Chen Wandun
2021-10-13 21:46 ` Shakeel Butt
2021-10-14  8:59   ` Chen Wandun
2021-10-15  1:34     ` Nicholas Piggin
2021-10-15  2:31       ` Chen Wandun
2021-10-15  7:11         ` Nicholas Piggin
2021-10-15 11:51           ` Eric Dumazet
2021-10-18  8:45             ` Chen Wandun
2021-10-16 16:46           ` Uladzislau Rezki
2021-10-14  9:29 ` [PATCH] mm/vmalloc: introduce alloc_pages_bulk_array_mempolicy to accelerate memory allocation Chen Wandun
2021-10-15 21:13   ` Andrew Morton
2021-10-16 16:27   ` Uladzislau Rezki
2021-10-14 10:01 ` [PATCH] mm/vmalloc: fix numa spreading for large hash tables Uladzislau Rezki
2021-10-15  2:20   ` Chen Wandun

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