linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210928153302.f87537b5faac8637c3c5eb53@linux-foundation.org \
    --to=akpm@linux-foundation.org \
    --cc=chenwandun@huawei.com \
    --cc=edumazet@google.com \
    --cc=guohanjun@huawei.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=npiggin@gmail.com \
    --cc=wangkefeng.wang@huawei.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).